C H A P T E R 5

DISCUSSION

CHAPTER 5

DISCUSSION

5.1 General

The salient findings emerging out o f the study have been discussed in this

section. Efforts have been made to support the findings with the relevant published work

of earlier scientists. The soil of the study site was sandy loam in texture, neutral in pH

and low in organic carbon content. It w as medium in available nitrogen and phosphorus,

while low in available potassium.

Potassium research is best appreciated in the context o f agricultural research

since bulk o f potassium is utilized on farms. Agriculture is a major cornerstone in

national economy of India and the country is still confronted with a substantially

increasing population pressure. Potassium is know n to be susceptible to luxurious

consumption under conditions o f excess potassium in the growth medium. Potassium

being an expensive input, it was considered desirable to know its optimum amount for

obtaining top yields. A large acreage of cropland in India is rain fed. Plants with

adequate potassium lose less moisture because o f the reduced transpiration rate. W hen

exposed to desiccating winds, plants suppHed with adequate potassium are able to close

the stomata much more quickly than potassium -deficient ones. Hence, it is useful to

assess the requirement for extra potassium in plants grow ing under conditions o f

moisture stress as well as in irrigated plants. Potassium is understood to help plants build

up resistance against incidence o f diseases and insect pests, lodging, m oisture

abnormalities. Field crops generally absorb potassium faster than they absorb nitrogen or

phosphorus. However, the rate o f K absorption during crop grow th differs with the crop

and the growth conditions. In the present scenario o f shrinking land and w ater resources,

bulk increases in crop production w ill necessitate a scientific use o f fertilizers.

Approximately 30-35 m illion tonnes o f N PK from fertilizers carriers, besides 10 million

tonnes from organic and bio-fertilizer sources, ai'e expected to be used by the year 2025.

Many soils, initially sufficient in native supplies o f soil potassium to raise a crop of 2 t

ha“’ may need external supplies o f potassium to produce a bigger crop o f 3-4 t ha~’. The

present study explores the effect o f varying rates o f applied K to screen out the high

potassium responsive variety o f Lens culinaris and to investigate how the varieties

respond to applied K along w ith rhizobium inoculation (Rhizobm m leguminosarum).ThQ

primary focus o f the first experiment w as to study the response o f eight varieties o f lentil

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to different levels o f K application. Varietal differences in nutrient efficiency observed

in the present study may be attributed to (a) the difference in the uptake efficiency o f

nutrients from the soil and /or (b) the differences in the use efficiency o f the absorbed

nutrients among varieties for production o f final yield. This study also explores several

physiological and morphological variables affecting K-efficiency.

Information on the interactive effect o f rhizobium and potassium in lentil is

insufficient. Nitrogen pkiys a critical role in plant grovs^th, as it is required for the

synthesis o f amino acids, proteins and DNA. Plants take up nitrate from the soil and by

reduction convert it to ammonia. Plants can take up am m onia directly from the soil but it

is present there in much smaller quantities compared to nitrate. A m m onia can also be

obtained by root nodules fixing atm ospheric nitrogen, by photo-respiring leaves and the

phenylpropanoid pathway. Ammonia enters the GS/GOGAT cycle where glutamate is

assimilated from glutamine and oxoglutarate. N itrogen use efficiency (NUE) at the plant

level is its ability to utilize the available nitrogen (N) resources to optimize its

productivity

Under conditions o f low availability o f soil K, together w ith im balanced N /K

fertilization in spinach production, application o f potassium enhanced nitrate uptake

stimulated the activities o f the nitrogen assimilating enzym es thus im proving the N U E of

the plants (A njana et al., 2009). NUE is critical for plant growth, crop biomass and

protein content as well as for optimal utilization o f fertilizers and bio-fertilizers. While

the amount o f N available to plants can be im proved by nutrient managem ent strategies,

the inherent efficiency o f the plant available N for the higher productivity needs to be

tackled biologically (Abrol et al., 1999; Abdin et al., 2005). N U E in plants is in fact a

complex quantitative trait that depends on a number o f internal and external factors in

addition to soil nitrogen availability such as availability o f other nutrients like potassium

(Anjana et al., 2006).

Potassium is important in optimizing both crop yield and econom ic quality. Root

activity and K uptake are generally reduced during the reproductive phase o f crop

development. This study has shown that supplem enting sufficient soil K w ith additional

foliar K applications during plant developm ental stages im proves plant growth and

sustainable crop production. Plants obtain K prim arily from the soil in the form of

which is strongly absorbed by soil com ponents, particularly clay particles, and is

therefore not readily mobile in most soils. A n experim ent was designed to evaluate the

67

effects o f foliar and basal K application on grow th and yield com ponents and to identify

the best combination o f treatments to improve production o f lentil.

The production of pulses in India is inadequate for the increasing human

population. The area under pulse crops can however, be increased if pulses are grown in

combination with other crops. Due to differences in rooting pattern, the m oisture

available in the soil profile may be utilized in a better w ay and thus increase the

combined crop productivity and water use efficiency (Singh, 1996).

Cereals intercropped with pulses have different fertilizer requirem ents from sole

crops. Moreover the high cost o f fertilizer and poor economic condition o f farmers make

fertilizer use risky (Singh, 1996). The amount o f nitrogen fertilizer applied could be

reduced by employing intercropping, as com pared to sole cropping e.g., wheat rows

intercropped with lentil. An experim ent was therefore designed to test the perform ance

of wheat sown in a particular row pattern with lentil under the influence o f applied N

fertilizer, along with the optimal dose o f potassium.

5.2 Performance o f lentil varieties in response to K application

The present study showed that potassium increased the root, shoot, leaf and

nodule fresh weight, fresh weights, and the num ber o f branches, leaves and nodules per

plant, up to a certain level (i.e., 50 kg K ha'^) o f application. This may probably be due

to the cumulative effect o f potassium on processes o f cell division and balanced nutrition.

We recorded a significant increase in seed yield per unit area over the control bu t again

there were more varietal differences where, in some varieties, the difference w as non­

significant. Seed yield is a function o f the com bined effect o f all the individual yield

components that are influenced differently by the various agronomic practices and

environmental factors (M uhammad, 2004). The current results are in line with those o f

Ahmed et al. (1988), Ghaffar (1990), Kar et al. (1989) and H alhday (1992) who have

reported differential response o f chickpea to various fertilizer doses. Poor yield response

of chickpea to varying levels o f fertilizer might be due to lodging at higher levels and

stunting at lower levels o f fertilizer, Boyer and Stout (1959) and Sarwar (1988) have

reported similar results in this regard. There w as an increase in agronom ic traits and

nutrient status o f plant grown with 50 k g ha'* K levels.

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5.2.1 Growth characteristics

The experiment was conducted for a com parative study o f eight varieties o f lentil

for their response to four levels o f potassium fertilization under similar environm ental

conditions w ith regard to growth, physiological, biochemical and yield characteristics.

Plant height and num ber o f branches plant"’ was significantly affected by

different rates o f potassium application. The results showed that potassium increased the

number of nodules per plant. On the other hand, shoot and root biomass increased at

different levels o f K. M oreover, under the field trials, 50 kg/ha"’ o f K improved the root

and shoot biom ass, though it was statistically non-significant. L atief et al. (2005) also

reported the similar results.

Highest leaf area was recorded with K 50 at flowering stage, which could have provided

adequate amount o f potassium. This shows that K has a marked effect in increasing the

leaf area at this growth stage. The variation in leaf area in response to potassium

fertihzation among the varieties selected was in conformity w ith the findings o f Shivay

et al., (2005) in barley. Similar observations have been reported for other crops e.g.,

wheat (Zhang et a l , 2004; A njana et al., 2006). The results o f im provem ent o f leaf area

by potassium application also conform to findings o f Chen et al, (1996), who reported

that potassium application increased the leaf area o f rape. The cause o f the increased leaf

area index is the greater accumulation o f K in K -fertilized leaves. Plants well supplied

with K expand their leaves and hence the leaf area (M engel and Arneke, 1982). Greater

leaf retention might be because o f an increase in the leaf area at later stages o f plants

fertilized w ith K.

5.2.2 Chlorophyll content of K-fertilized lentil varieties

Many authors have established that chlorophyll synthesis is dependent upon

mineral nutrition. In the present study, leaf chlorophyll at the various growth stages o f

lentil revealed significant varietal differences in response to applied K. Chlorophyll

concentration, leaf surface and dry m atter w eight can be used as potential indicators for

nutrients deficiency in the soil (Tejada-Zarco et a l , 2004). A pplied potassium was found

to increase chlorophyll content o f leaf, conform ing to the observation o f Bark and Chein

(1983). Presumably, potassium application prom oted the uptake o f such nutrients as

SO4, Fe^”̂ and Mg '̂*' that are known to be associated w ith the synthesis o f chlorophyll.

Nitrogen is a structural elem ent o f chlorophyll and protein m olecules and thereby

affects formation o f chloroplasts and accum ulation o f chlorophyll in them (Tucker, 2004;

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Daughtiy et a l , 2000). N concentration in green leaves is thus related to chlorophyll

content, and therefore indirectly to photosynthesis (Haboudane e t al., 2002; Amaliotis et

al, 2004; Lelyveld et al., 2004; Cabrera, 2004). O f all macro metabolic elements, the

greatest influence on developm ent o f plants and their leaf surface is exerted by nitrogen,

which is enhanced by potassium.

5.2.3 Nitrate content and NR A of K-fertilized lentil varieties

Significant differences in leaf nitrate content and nitrate reductase activity (NRA)

were observed among varieties o f lentil. Interspecific and even intervarietal variations in

nitrate content and NRA have been reported earlier also (H arada et al., 2003; Jiang and

Hull, 1998). NRA can be influenced by many factors such as light (Lilo, 1994),

temperature (Harris and W hittington, 1983) and nitrate supply (Li and Oaks 1993). In

the present study, these factors are com mon for all the varieties. Different shoot organs,

root tissues and growth stages also influence NRA. These factors were also elim inated as

variables by using the same tissues in similarly aged plants at the same tim e for all the

varieties compared. Therefore, difference in N RA m ust have represented the actual

varietal variation to the applied potassium, as m ost o f the param eters of N metabolism

are directly influenced by dose applied (Ruiz and Romero, 2002). The variation may

be attributable to nitrate-reduction system in the shoot, nitrate-uptake system in the roots

or both of them, because shoot NR is synthesized de novo in response to nitrate supply

from the roots (Li and Oaks, 1993).

One o f the major and limiting events o f nitrate assim ilation is N R activity

(Campbell, 1996; Huber et al., 1996). There is a reverse relationship betw een nitrate

content and NRA (Olday et al., 1976). So accum ulation or assim ilation o f nitrate in cell

depends upon activity o f nitrate reductase. By com paring nitrate content and N RA of

different treatments at various growth stages we found that increased N R activity

decreased nitrate accumulation in leaves o f lentil. Consistent w ith previous studies

(Sorour et al., 1998), this m ay indicate that availability o f K to the plant was a factor

affecting the shoot distribution o f N RA which in turn affects nitrate content,

5.2.4 Variations in total soluble protein content o f K fertilized lentil varieties

Many studies have been carried out on variation in protein content among

varieties and genotypes (Khatib et a l , 2002; Riblett, 2001). Furtherm ore, protein

composition varies among genotypes and is influenced by the environm ent (Mejia,

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2004). Several biological processes contribute to differences in protein content and

quality among varieties, including the presence o f nutrients as reported by Phillips et al.

(1982). Varietal differences in protein content under the influence o f applied potassium

were also apparent in our study.

The protein content tends to increase with the increase in K application,

compared w ith the control. The best protein yield was obtained w ith K50 and K75

concentrations. This could be attributed to the role o f K in biochem ical pathways in

plants. K has favorable effects on the metabolism o f nucleic acids and proteins (Bednarz

and Oosterhuis, 1999). Our results w ere in agreement with those obtained by Abou El-

Nour et al. (2000) and Ghourab et al, (2000).

5.2.5 C/N ratio and K contcnt

The test varieties o f lentil showed significantly higher K accumulation in leaves

as a result o f K application, K 50 giving the optimum value. Thus K50, equalled with K 75,

interacted m ost beneficially with all varieties.

Significant negative correlations were found between C/N ratio and % N losses by plants

and between harvest index and % N losses. It implies that plants having high C/N ratio

and harvest index also have less nitrogen losses from plants. M oreover, such plants

possess higher NutEs, which is evident from significant positive correlation o f N utE

with C/N ratio and harvest index, and from significant negative correlation between % N

losses and NutEs o f plants.

5.2.6 Yield characteristics

The effect of potassium application rate was highly significant tow ards 1000-

seed weight. The results are in line w ith those o f Sharma et al. (1992) on some Brassica

cultivars. The results suggest distinct changes in seed w eight and quality in the presence

of added K, thus confirm ing the findings o f M ullins et al. (1991) and Cassman et al.

(1992). The increase in the seed w eight m ight be due to the effect o f K on mobilization

of photosynthates, which would increase seed w eight (Cakm ak e t al., 1994).

5.3 Variation in H K R and LK R in response to K and Rhizobium

A critical aspect o f rhizobium-legume association is the fact that it is often

manipulated under nitrogen-limiting field conditions in such a w ay that crop production

could be enhanced easily and inexpensively (Hubbell et al., 1979; Freiberg et al., 1997).

71 .

The amount o f nitrogen fixed, depends upon the presence o f effective nodules on the

host roots which are a prerequisite for the potential gain o f nitrogen from the system.

Although, the rhizobia commonly occur in soils bu t often fail to cause nodulation, often

because of some unspecified type o f antagonism that prevents root colonization by the

I'hizobial strain (Jadhav et al., 1994). Inoculation is a m anagem ent practice by which the

rhizobium-legume symbiosis is exploited through overcom ing nodulation failure or

ineffective nodulation. Bermer et al. (1990) carried out a screening program to evaluate

the effectiveness o f i?. leguminosanim for lentil.

Inoculation significantly increased the num ber o f nodules. Strain L-2097 (RHZ2)

produced the m ost nodules, w hile the uninoculated treatment (indigenous population)

produced the fewest. The L-2097 and L-1897 strains produced the maximum and the

rninimum m imber of nodules per plant in HKR, respectively. The strains differed

significantly in nodulation, however all resulted in better nodulation than the

uninoculated control. Some inoculant strains were successful in dom inating the

formation o f nodules even in the presence o f active indigenous com peting rhizobia

(McLoughlin 1984).

5.3.1 Growth characteristics in response to K and Rhizobium application

It was observed that efficiency o f Rhizobium is influenced by the availability o f

K in the soil as it was directly involved in the nutrition o f legum e and also helps to

improve the root as well as shoot grow th of the crop. Thus, it can be used as an

alternative o r a supplement to the chem ical nitrogen fertilizer to increase agricultural

production w ith lesser capital input and energy.

Application o f inoculums and potassium fertilizer significantly affected the

number of nodules and the treatments significantly differed from each other. The highest

number o f nodules per plant was observed in seed inoculation + 50 kg K ha"'.

Ramaswami and Oblisami (1986) reported increase in the num ber o f nodules due to

inoculation application.

Rhizobium spp. invade the root hairs o f lentil and result in the form ation o f

nodules, where free air nitrogen is fixed. These bacteria, although present in m ost o f the

soils, vary in number, effectiveness in nodulation and N-fixation. It has been argued that

usual native soil rhizobial populations are inadequate and ineffective in biological

nitrogen fixation. To ensure an optimum rhizobial population in the rhizosphere, seed

inoculation o f legumes w ith an efficient rhizobial strain is necessary. This helps improve

72

nodulation and yield o f leguminous crops (Henzell, 1988). A lthough, this crop is capable

of fixing atmospheric nitrogen through Rhizobiinn species living in root nodules, yet

under our agro-ecological conditions, nodulation o f lentil is poor and is a major cause o f

its lower yield. It was observed that inoculation o f m ungbean with Rhizobium spp.

increased plant height, leaf area, photosynthetic rate and dry m atter production (Thakur

& Panwar, 1995).

Greater plant height was observed in response to inoculation alone as well as

rhizobium inoculation along with 50 kg K ha‘‘. These results are in line with the findings

of Patra and Bhattacharyya (1998), who reported that seed-inoculated plants exhibited

significantly greater root and shoot length, as compared w ith un-inoculated control

plants. Application o f inoculum and potassium significantly improved plant height.

Potassium fertilizer @ 50 kg ha"', in com bination with inoculation, increased plant

height over the control, while other treatm ents were at par w ith it. Com parable results

were obtained by Sindhu et al. (1999). It mEiy be concluded from the data and the above

discussion that growth o f lentil seedlings can be enhanced by inoculating seeds w ith

effective rhizobial strains. They stated that inoculation w ith rhizobium increased the

growth, yield and nutrient uptake significantly in pot and field experiments.

53.2 Photosvnthetic rate and stom atal conductance

The HKR variety shov/ed higher stom atai conductance and net photosynthetic

rate than the LKR by maintaining a h igh K concentration in the lower leaves also and

maintain a large pliotosynthetic capacity.

HKR variety photosynthesized at a greater rate per unit leaf area than the LKR,

This superior photosynthetic performance o f one genotype can be partially explained by

its greater leaf chlorophyll content relative to that o f other varieties. The reduction in

leaf size m ay have concentrated the am ount o f photosynthetic m achinery per unit leaf

area. These results support the findings o f Pettigrew (2004), who found variation in

performance o f cotton varieties grown under similar conditions. The genotypic variation

in photosynthesis in rubber was also reported by G unasekara et al. (2007).

Photosynthetic rate o f the same genotypes showed a m arked difference in studies on rice

(Sarker et al., 2 0 0 1 ; Tang et al., 2 0 0 2 ).

A variation in the stomatal conductance, an im portant character determining the

loss o f water, was observed in varieties studied, A pplication o f K im proved the stomatal

conductance in both the varieties in varied magnitude. Potassium influences the

73 .

photosynthesis process at many levels, namely; synthesis o f ATP, activation o f enzym es

involved in photosynthesis, CO2 uptake, balance o f electric charges needed for

photophosphorylation in chloroplasts and the light-induced flux across the thylakoid

membranes (Marschner, 1995). Photosynthesis requires adequate K levels in lea f tissue

and lower K levels have been found to decrease photosynthetic rate sharply in corn

(Smid and Peaslee, 1976). Debnath (2005) observed that net CO 2 assim ilation in litchi,

under high irradiance and high am bient CO2 concentrations, increased at high rates o f K

application.

5.3.3 Leghaemoglobin content in response to K and Rhizobium application

Legheamoglobin (Lb) is the red pigm ent commonly found in the root nodules

that develop on leguminous plants. Varieties differ significantly in leghaem oglobin

content of nodules, Legheamoglobins are haem oproteins consisting o f an iron porphyrin

and a peptide. In lentil, significant increase in leghaem oglobin content was observed

with L-2097 (RHZ2) inoculant o f rhizobium. Similar results w ere reported by Sharm a et

al. (2006) in mungbean, urdbean and pigeonpea.

5.3.4 Pro tein content (nodules, leaves and seed) in response to K and rhizobium

Potassium has an irreplaceable part to play in the activation o f enzym es that are

fundamental to metabolic processes, especially to the production o f proteins and sugar.

In the present study, K supplementation increased the soluble protein contents in the

leaves. The significant effect o f K application m ight be due to a better K utilization.

Authors like M arshner (1995) and K aya et al, (2001) hold that adequate am ount o f K'^is

specifically required for protein synthesis and en2ym e activation.

Protein content o f nodules and seeds o f both the genotypes w as significantly

affected by added K level, K 50 resulted in maxim um protein content o f HKR,

Consequently, K50 x H K R and K50 x LK R proved to be the best interactions, yielding the

maximum protein content in the seed. However, with K 50+R H Z2, both the varieties

proved at par. In fact, K facilitates the uptake as well as assim ilation o f nitrogen into

simple amino acids and amides and therefore enhances peptide synthesis, leading

ultimately to protein synthesis (Sodek et al,, 1980).

In the present study, Rhizobium inoculation and K fertilization significantly

increased seed protein content in HKR+RHZ2. The effects o f inoculation on seed protein

content vary from no effect (Vaishya and Dube 1991) to a highly significant increase

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(Kumpawat,1994). Barran et al. (1999) also reported that inoculation o f R hizobiim

increased protein and nitrogen contents of bean. This could probably be attributed to an

increase in the nitrogen-fixing efficiency o f inoculated plants where m ore nitrogen is

fixed and translocated to the seeds. Rhizobium spp. inoculation has been reported to

increase seed protein range o f soybean (Koutroubas et a l , 1998) faba bean (Cordovilla

e ta l, 1999)

5.3.5 Effect of potassium and Rhizobium on nitrate, N -m etabolizing enzymes and

C/N ratio

According to Stitt (1999), nitrate sensing provides one o f the mechanisms

whereby plants sense N availability in the environm ent and their internal N status. A t a

cellular level, it leads to reprogram ming o f m etabolism to allow nitrate to be assimilated

and incorporated into organic com pounds, and at a whole plant level, it modulates

allocation and development to allow root growth and nutrient uptake and temporal

fluctuations in the availability o f nitrate. Signals might be derived from nitrate itself,

from metabolites formed during nitrate assim ilation or m ore directly as a result o f

changes in other cell constituents or the overall rate o f growth. In addition, signals

originating from downstream events may exert negative feedback regulation on earlier

steps in nitrate acquisition. In a given situation, it is likely that several signals interact to

condition the observed response. N itrate induces genes encoding the high and low-

affinity nitrate uptake systems, for nitrate reductase, nitrite reductase and the enzyme

required for ammonium assimilation v ia the GOGAT pathway. The increase in transcript

is accompanied by increased rates o f nitrate uptake, increased nitrate reductase, protein

and activity and increased activity o f nitrite reductase and glutam ine synthetase. N itrate

assimilation requires synthesis o f organic acids, especially a-oxoglutarate w hich acts as

the acceptor for ammonium in the GOGAT pathway, and m alate which acts as a counter

anion and substitutes for nitrate to prevent alkalinisation. To fulfill this requirement,

nitrate also induces genes required for synthesis o f C-acceptors like a-oxoglutarate, the

synthesis o f organic acids like malate to m aintain pH balance and in non-photosynthetic

tissues, and also induces genes required to generate redox equivalents during respiratory

metabolism. Therefore, nitrate leads to rapid changes in the levels o f a wide range o f

transcripts encoding enzymes in nitrogen and carbon metabolism. This allows

reprogramming o f N and C metabolism, to facilitate the assim ilation o f nitrate and

incorporation into amino acids. M oreover, a simultaneous increase in all N -m etabolizing

75

enzymes together with increase in nitrate concentration in both HKR as w ell as LKR

genotypes, lurthcr supports the hypothesis that the whole sequence o f enzym es functions

in a coordiiialed manner in order to assimilate nitrogen in plants.

The N fixed by legume docs not affect only the N cycle o f natm-e, but is also o f

economic importance, 'fhus, greater attention should be paid to the question o f whether

the nutritional .status o fth e host plant has a major influence on N fixation by Rhizobium.

Iherefore. legunies well supplied with inorganic nutrients are supposed to fix

more N2 by their root nodule,s than plants that are deficient in one or the other element.

This may be a result o f an indirect effect o f plant nutrients, because plants well supplied

with nutrients producc more leaf matter, resulting in an increased CO2 assim ilation by

the plant. The fact that photosynthesis favours N2 fixation by root nodules has been

reported by variou.s authors (IJndstrom et a l , 1952). This possibly leads to an improved

supply o f carbohydrates to the roots so that num ber and size o f the nodules will be

increased.

That such an effect is exerted by also, can be seen in present study. This

finding alone, however, cannot explain the increased N 2 fixation o f nodules from plants

well supplied w ith K ’, becausc the K effect on Na fixation per plant was considerably

higher than the K effect on nodule size or number. The beneficial action o f improved K

supply on the growth o f the host phints does not furnish a satisfactory explanation as a

higher N distribution occurred in various plant parts. Therefore, it indicates that N

turnover o f (he root nodule.s was improved by K ^ It means that the amount o f sugars,

and in particular that o f C-labeled amino acids per g fresh weight o f root nodules,

increased with increa.sing K supply to the host plant (Mengel et a l , 1974).

'fherc m ight be a connection between this K effect and the provision o f

Rhizobium hacteroides w ith carbohydrates. According to V iro and Haeder (1971), K' ̂

promotes the translocation o f carbohydrates in higher plants. This may also hold true o f

legumes. M engel et al .(1974) found higher contents o f starch and sucrose in the roots o f

Mcdicago sadvu and Trifolitmt pratense well supplied with K than in plants given low er

K applications. 'This m eans that in some way had a beneficial effect on the formation

o f reduccd N (N H 3). I f K" exerted an effect only on the synthesis o f keto acids as a result

o f a better supply o f carbohydrates to the roots, there had not been such a great

difference between the labels o f sugars and am ino acids w ith increasing K supply.

Rather an opposite effect was to be expected in this case, m eaning that a high supply o f

C skeletons had led to a relative shortage o f reduced N, Carbohydrates provided by the

76

host plant t(> R bhahiuim baeteroides affcct the m etabolism o f the latter. In these

processes, ifu; tricarboxylic acid ( I C A ) cycle plays a decisive part. It supplies the

iiitrogcnasc with clccircins aud ATP, required tor the reduction o f N i t o N H 3.

It appears that improved carbohydrate supply to the root nodules as a result o f the

action of K ■ ma} result in a better provision o f the nitrogenase system with electrons

and ATi', In (his respcct. observation ol' Gukova and Tjulina (1968) that root nodules

with a good capacity o i'N i llxalion are rich in is o f interest.

the yield iuul vieid com ponents of HKR and LKR varieties in response to K

and Rhhoh'ium

All !e\'c!s ofpt^lassiuin resulted in significantly higher pod yield over the control

in both tlic gcn(U\‘pes. Yield is tJic fmal manifestation o f several complcx agro-

physiologicai paniinctcrs. Ihe yield performance o f the genotypes could be the

rcllection o f the physi(»logicai paranieter.s a.s well as yield attributes recorded, most o f

which behaved similarly as pod yield. O f the varieties, H K R proved invariably better

than LKR. as retlcctcd by pod yield o f the two genotypes. Hoque and H aq (1994) also

reported that seed inoculation increased num ber o f pods per plant in lentil. Rashid et al.

(1999) reported lliat R hto in inn inoculation + 20 kg N ha"' increased pod yield

signiJ!caiu!y.

A.s to the hiirvx'.st index, varieties differed significantly with increasing levels o f

applied polassium . R1 i/.2 proved lo be the best for harvest index of HKR, giving a

higher \'alue than the control. HKR perform ed best in this respect with K 50 and showed

an increase over the control. Two best interactions, viz. K50 X RHZi and K50 X RHZ2,

gave statisticall)' similar valuc.s indicating that K application a t 50 kg K2O ha '' rendered

the two genotypes with proportionate partitioning o f assimilates. H owever, due to

inherent .superior performance o f HKR in com parison to LKR, K application also

resulted in higher yield o f f IKR than LKR.

'fhe inoculated plants with Rhizohium spp. produced more seed weight than

control. Sim ilar results w ere obtained by Shisanya (2002), who found a significant

increase in bean inoculated with Rhizobium strains, and inoculation increased 100 seed

weight o f guar (Llsheikh and Ibrahim, 1999).

Seed yield per plant was significantly affected by Rhizobium inoculation and

fertilizer appHcation.s, Chatterjee and Bhattacharjee (2002) reported that the percentage

increase in grain yield over the control was significantly higher in plants inoculated with

77

Rhizohium stiains Mtid phospfiate-solubilizing bacteria. Sim ilar results have also been

reported by (iupta (:2()(35) in ciiickpea and Brhamprakash et al. (2007) in food legumes.

1 hcrclbrc, it n ia \ be concluded that yield and yield com ponents of lentil crop were

significantly increased due tt) inoculation and fertilizer applications. The overall

potassium tcrliiizalion along inoculation was more effective and gave better results than

the rhi/.obium inoculation alone.

5.3.8 Lcitf K con tent

Potassiiun is highly mobile in plants and differences between varieties in

cfnciedcy oi K utilization have been attributed to difference in capacity to translocate K

at cellular level and whole plant level. Under K deficiency, cystolic K'̂ activity is

maintained at the expense o f \ acuolar activity (Leigh 2001, M emon et al. 1985), even

though vacuolar (but not cystolic ) K* activity is regulated differently in the root and

leaf cells (C 'ulin et al.,2(1(13). M obilization o f vacuolar K into the cytosol was particularly

strong in K -eftlcient than in K-ineffieient barley genotypes (M em on et al., 1985).

Capacit}' to translocate K between organs may also be an im portant mechanism

for efficient utilization o f K within the plant (in ryegrass; Dunlop and Tomkins, 1976).

Capacity to translocate K from non-photosynthetic organs such as stems and petioles to

upper leaves and harvested organs can influence the genotypic capacity to produce a

high economic yield per unit o f K taken up. Two K-efficient rice genotypes had a two­

fold higher K concentration in lower leaves, but only 30% higher K concentration in the

upper leaves, compared with K-inefJicient rice genotype at the booting stage (Yang et al.,

2004).

S.4.I E ffect of fo lia r K fertUi/ation on H K R an d LKR ientii varie ties

Foliar feeding seems to be one o f the easiest ways o f increasing growth speed,

yield and quality. A favourable effect o f foliar fertilization on the plant growth and

development w as e.stablishcd by Peuke et al. (1998).

Being a multifunctional versatile nutrient indispensable for plants, K is

functional in several processes such as enzym e activation, stim ulation o f assimilation

and transport o f assimilate, anion/cation balance as well as w ater regulation through

control o f stom ata (Krauss and Jin Jiyun, 2000).

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5.4.2 Effect o f biisat and foliar K fe rtili/a tio n

DuUa et ai. (200!) and Ali and Mowafy (2003) indicated that adding potassium

ferliii/.er siunilicantly increased number ol' branches. Foliar potassium fertilization has

been sueccsslu! lor citrus and other fruits (Uriu et a l , 1990; D iver et a l , 1985). Thalooth

et a!. (2 (K)6 ) reported that K was eflectivc in improving the area, num ber and weight o f

leaves per piaiil. Number ol pods per plant showed an increase when potassium was

applied both as Ibliar a!id soil treatnicnts. Increase in pod num ber determines the yield o f

crops. Iherel'ore foliar ? soil application gave positive results in increasing the yield.

However, ibliar islojic application gave lower values on an average than foliar + soil

application, riie results are in accordance with those o f Salwau (1994), Ram amoorthy et

al,. (199.5) recttrdcd sim ilar results in black gram and Ahmed and M ohammad (1991) in

apple. /\ccording to Ch\)wada and Growada (1980), number o f pods plant increased with

NPK application in raiHala. However, Ghadiyal (1992) found that foliar

application incrca.sed num ber o f pods in the same plant. The difference might be due to

the diriercnt nutrient status o f soils. In the present study, best results were shown by

foliar i basal application treatments. Singh and Kamath (1989) reported that foliar

application was not superior to soil + basal application. H igher basal fertilizer dose was

more effective (N atecs et a!., 1993) than foliar alone application.

Mengei and Kirkby (1987) stated that foliar application o f plant nutrients can be

very eflicient untier ccrtain conditions but it should be born in mind that leaves are able

to take up relatively small quantities o f nutrients in com parison with the plant’s demand.

At the same time. Oosterhuis (19% ) stated that Ibliar feeding o f a nutrient may actually

promote absorption o f the same nutrient, leading to increase in the crop yield and reduce

the quantities o f fertilisers applied through soil (A hm ad,1998). The positive effect o f soli

application o f K .supplemented with foliar K feeding on lentil could therefore, have been

due to the better K nutrition which im prove pod setting and leads to stimulate the storage

capacity for assim ilates which in turn, induces rem arkable increase in seed weight and

number o f pods per plant. 13eringer (1980) drew similar conclusion and added that better

K nutrition improved nitrogen metabolism by stim ulating the activity o f nitrate reductase

to promote the formation o f peptides and proteins. Generally, increasing lentil yield

would find an interpretation through metabolic function o f K in plants. For instance,

Oosterhuis (1998) reviewed the im portance o f potassium for p lant growth. He mentioned

that K is not a constituent o f any know n component, but it is im plicated over many

processes in the plant. In this regard, Bednarz and Oosterhuis (1996) found that

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chlorophyll content in cotton plant leaves decreased under K deficiency, leading to high

reduction (up to 95%) o f leaf photosynthesis. Roemheld and El-Fouly (1999) explain

why the efficiency o f foliar fertilization is higher than that o f soil application. They

reported that one reason is because o f the supply of the required nutrient directly to

location o f demand in the leaves and its relatively quick absorption.

Concerning leaf macro and micronutrient concentrations, it is quite clear that

despite that some nutrients v/ere increased and some others were decreased due to K

treatments, the dry matter production in terms o f seed and straw yields showed great

increase, as compared w ith the negative control treatment. This means that the uptake o f

nutrients was generally increased. Hence, the insignificant decrements in some nutrients

could be the result o f dilution effect.

Previous research by Nelson and Motavalli (2001, 2002) on crop response to

foliar application o f K sullate on the soybean at stages o f development, demonstrated

that soybean grain yield increased over 10 bu/acre, when compared to a non-treated or

MgS04 control.

The concentration o f mineral nutrients in the soil solution, i.e., the available

nutrient concentration, varies over a wide range, depending on many factors such as pH,

soil organic matter and fertilizer application (Marschner, 1986). Fan et al. (1999) found

that K content in petioles and total dry matter production increased by applying K to

cotton plants. Gormus (2002) indicated th a tth e 0 kg K2O ha"’ plots (untreated or control)

had a lower leaf K concentrations, compared with the other plots, when fertilized with

K2O levels at the rates o f 80,160 and 240 kg K2O ha"’. A neela et a l , (2003) indicated

that K content significantly increased with increasing K2O levels and was the highest at

200 kg K2O ha"’. Our results endorse these findings. The pod and dry matter yields o f

lentil v/ere significantly higher when 50 kg K2O ha"’ was applied as basal dose to the soil,

as compared to the foliar K treatments alone, iiTespective o f the K source used for foliar

application, crop variety and growth stage. Our findings here are in confirmation with

Abaye, (1996) that combined soil and foliar K application w as better than the soil alone

or foliar alone application of K in cotton. Assim ilation and translocation o f

photosynthates are favoured by K"̂ . High levels o f photosynthesis and large numbers o f

seed are characteristics o f high yield en'vironmeiits, while the converse is true in low

yield ones.

Developing pods have a high K requirement, therefore it is critical to provide an

adequate potassium level to plants to recover the fixed K and prevent K deficiency. This

80

K rcquitcmciil can i>n!y be met by plant soil K application, hence higher yields were

obtained with basal K application than with the foliar alone K treatments. Potassium

uptake by plants I’roni the .soil is regulated by several factors including texture, moisture

conditions, pH. aeration and temperature (Mengel and Krikby, 1980). Clay soils can

absorb and hold more K and exchange it with soil solution for plant uptake than sandy

soils. Both Ca and Mg compote with K ' for root uptake, hence plant grown in these

soils often exhibit K dcik iencies even though soil analyses indicate adequate K. Thus,

when toliar spray was done along with basal K application, the crop yield was

significantly higher than the .soil application alone. Foliar application o f 0.50 % K 2SO4

combined with basal (50 kg K ha"') application produced the highest pod and dry m atter

yield and these w'cre significantly higher than the same treatm ent with 0.50% KCl. The

same was obser\'ed for all the yield and quality contributing param eters like number o f

pods, 100 seed weight, seed yield per plant, harvest index and protein content o f seeds.

The K content in the leaves and K uptake by crop were also m aintained at higher levels

with 0.50% K2SO.,.

K requircment.s o f ti.ssues are generally attributable to differences in K

requirements in tlie vacuoles and apoplast as well as capacity to m aintain cystolic K at

certain level, lifficienl utilization o f K during the vegetative stage may not translate into

K efficiency for economic yield. The genotypic diiTerences in harvest index influenced

the efficiency with which K could be utilized to yield grain more than the capacity to

utilize K to produce biom ass (e,g, in wheat; W oodend and Glass, 1993).

I ’hc enhancement o f K content in plant dry m atter was optimum with the

RHZa+Kso do.se in HKR. Several studies have found that K fertilization usually

increases K concentration o f vegetative plant parts (Yin and Vyn, 2002a, 2002b; Borges

and M allarino, 2003; Yin and Vyn, 2003). Typically, K tissue concentration ranges

between 3% and 5% (Tisdale et al., 1985). Leigh and Johnston (1983) found a

significant positive correlation (r = 0.76; P < 0.001) between K concentration in leaves

and the grain yield o f spring barely.

Under the present experimental conditions, it could be concluded that foliar

fertilization as supplem entary potassium application can not only reduce the am ounts o f

soil potassium application, but also can have a positive effect on yield and its quality.

81

5.5.1 Effect of N and K fcrtiU /ation on In terc ropped w h ea t

Lentil being a legume has the ability to fix atm ospheric nitrogen in the soil in

association with specilic rhizobiu. Lentil could derive two-thirds o f its nitrogen needs

from the atm osphere (I^adarnch, 2()05). At maturity, the level o f symbiotically fixed

nitrogen in two years has been reported to be 154 and 117 kg N/ha in mono-cropped

lentil and 95 and 41 kg N /ha in lentil intercropped with barley (Sehmidtke et a l , 2004).

Use ol bio~inoculants Rhizohiimi spp. and Azckspirillium brasilem e helps in enhancing

nodulation in lentil ( l iwari and Misra, 2000; Kumar and Chandra, 2005) and thereby

nitrogen fixation. Therefore, these inoculants may need to be used to ensm-e greater

inputs of nitrogen fixation in lentil based intercropping systems.

Nutrients, such as K, P, Mo and S, reportedly have a major effect on the legume

component (Andrew, 1977), and add competitive ability to the legum e component in

legume/grass mixtures in response to K application (Blasser, 1950; Bremner, 1982;

Russel 1978). However, inform ation available on the effect o f K on the growth of grain

legumes/ccreal intercropping system is scanty. Legum e/cereal intercropping systems

occupy a prominent place in agricultural systems o f the tropics (Ofori, 1987). Studies

done by Ciuiiasekera and Henaratne (1990) have shown that application o f appropriate

level o f K (i.e., 80 kg ha“') on maize-m ungbean intercropping system alleviated the

competitive depression o f mungbean in dual stand. Hegazy and Genaidy (1995) reported

that application o f potassium sulphate improved the growth o f soybean when either

mono- or intercropped on clayey soil. The relative K-fertilizer efficiencies were reduced

in intercropping, compared with mono-cropping, thereby, increasing the economic

optimum K-fertili/.cr rates.

I . c a f chlorophyll conten t is one o f the key factors in determ in ing the rate o f

photosynthesis and dry m atter production (Bellore and M all, 1975). The sole lentil

recorded com paratively higher chlorophyll content than th e in te rc ro p p ed lentil.

The c o n v e r s e w a s observed in the case o f wheat. The tall-grow ing intercropped

wheat significantly affccted N fixation ability o f lentil. Lim ited ability to obtain sunlight

by the soybean shoots might translate into major competitive lim itation (M idmore, 1993)

that strongly influences the interspecific com petitive ability. The reduced light energy

affects N2 fixation by restricting photosynthesis and the energy supply to roots, thereby

reducing nodulation and nodule size (N am biaret a l , 1986).

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5.5.2 Effect.of_N_.aiid K fertilization on nitrate and N -m etabolizing enzymes in

intercropped wheat

N itrate is th e p red o m in an t N form in most soils. However, su ffic ien t N R

activity is a p re req u isite for an optimal u t i l i z a t io n o f soil nitrogen (Beevers a n d

Hageman, 1969). In th e present s tu d y , the N R activities and chlorophyll content in

in tercropped wheat w e r e re la t iv e ly g r e a t e r th a n in th e sole w h e a t. O ur

r e s u l t s f u r t h e r show ed higher N R activities in leaves, indicating th e p r e s e n c e

o f h ig h e r n i t r a t e c o n c e n t r a t i o n in leaves than in roots. The level as well as

the d istribu tion o f enzyme activity between the different plant organs, however,

varies among species apparen tly due to th e ir natural habitat (Lee and Stewart,

1978) and also d epends on the developm en ta l stage o f the plant (Pate, 1980).

Lexa and C heesem an (1997) f o u n d that changing the location o f nitrate

reduction did not change g row th significantly and caused only subtle changes in

N concentration , 'fhe favourable effect o f the in tercropp ing system in increasing

c h lo ro p h y ll c o n te n t a n d N R activ ity may have resulted in higher dry m atter

p ro d u c tio n . The y ie ld in crem en t o f sorghum in soybean -so rghum in tercropp ing

may also be due to transfer o f N fixed by soybean to sorghum (A g b o o la an d Fayemi,

1972; Burtcn e t a!., 1983). As there is a reverse relationship between nitrate content and

NRA (Olday et al., 1976), accum ulation or assim ilation o f nitrate in cell depends upon

activity o f nitrate reductase (NR). By comparing nitrate and N RA o f different treatm ents

at various growth stages we found that increased N R activity reduced nitrate

accumulation in lentil leaves. It shows that application o f N fertilizer without K can

increase nitrate accumulation in leaves. The difference in nitrate and NRA in different

treatments was apparent at all the growth stages. N RA and nitrate in leaves also

decreased w ith plant age. Resuhs o f our study suggest that potassium application

reduces nitrate accumulation, which is in accordance with th e findings o f A hm ed et al.

(2000) and Ruiz and Romero (2002), who reported that increase in the rate o f potassium

application facilitates the uptake and transport o f nitrate towards the aerial parts o f the

plant, prom otes the m etabolism and utilization o f nitrate and ultim ately, reduce nitrate

accumulation in crops. Phosphorus, potassium and sulphur have m ajor roles in

production of proteins thereby decrease nitrate w ithin the p lan t (Brown et al., 1993).

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5.5.3 Seed yield in intercropping

The seed yield ol intercropped wheat, as compared with sole wheat, increased

while that o f intercropped lentil showed no increase. It appears that lentil did not

benefit from the intercropping as m uch as wheat. Thus, the results ascertain that wheat

was the m ajor contributor to the mixture yield. Ghafferzadeh et al. (1994) also observed

yield increm ent o f maize and yield decrem ent o f soybean in a maize/soybean strip

intercropping system, as compared with the corresponding sole crops. The greater

ability o f sorghum to absorb limited soil factors increased the interspecific competition

in the intercrop (Trenbath , 1976). Lentil, when grown as sole or intercropped with

wheat, produced yield advantage on succeeding finger m illet equivalent to 19.81 and

10.38 kg N/ha, respectively (Prakash et a!., 1991). In such intercropping growth

depression has often been observed, c.specially w h en N fertilizer is applied (Chui, 1984;

Dalai, 1977; Ofori, 1987), Greater increase in intercropped wheat yield was evident

mainly from the increase in above- and below-ground biom ass, chlorophyll and NR

activity. The yield increment o f wheat among these three belowground components o f

both the intercrops obviously had greater effect on yield advantage in the intercropping

system. D eclining yield trends due to fertilizer treatm ent in all crops under both sole

and intercropping systems were statistically non-significant.

84