C obbina, J .1, K. M ulongoy2 and A. N. A tta-K rah1. 'H um id Z one Program m e, International Livestock C entre for Africa, P.M .B. 5320, Ibadan, Nigeria; in te rn a tio n a l Institute of Tropical A griculture, PM B 5320, Ibadan, Nigeria.

SO IL FACTORS INFLUENCING INITIAL GROW THO F LEUCAENA AND GLIRICID IA IN AN ALFISOL

O F SOUTHW ESTERN NIGERIA

In tro d u c tio n . L eucaena (Leucaena leucocephala (Lam.) de W it) and gliricidia (Gliricidia sepium (Jacq.) Steud.) are two m ultipurpose tree /sh ru b species which have been found suitable for alley farm ing (K ang et al. 1984). They com bine good coppicing ability with excellent biom ass, foliage nitrogen, and crude protein yields. However, they are often slow to establish in som e farm ers’ alley cropping systems. Difficulty of establishm ent has been attributed to m any factors including poor soil fertility status (Cobbina et al. 1988). T he purpose of this study was: (i) to com pare the early grow th and nodulation of the trees in greenhouse in two soils, and (ii) to determ ine the response of the trees to application of N and P fertilizers and inoculation with rhizobia, as corrective m easures in the two soils.

M ate ria ls an d m ethods. T he experim ent consisted of a factorial com bination of two soil types, two ra tes of phosphate (0 and 50 mg P /k g soil as C a(H 2P 0 4)2H 20 ) , and four sources of n itrogen (none, u rea at 100 mg N /k g soil, inoculation with a local strain o f Rhizobium , IR c 1045 (L j), and inoculation with an elite strain of leucaena R hizobium (E 2)). These treatm ents were fitted in to a random ized com plete block design. B oth soils w ere loamy sand Alfisols; one was collected from an alley cropping farm w here the trees had chlorotic leaves (poor soil) and the o ther soil from a farm w here the trees had green leaves (fertile soil) (Table 1).

T able 1. Some charac teristics of the two soils used.

Soil Textural PH O rganic Total Available Exchangeable cationsclass C N P1 -meq/lOOg-

-% - -ppm- Ca M g K

P oor Loam y sand 6.6 0.74 0.053 3.6 1.88 0.63 0.11F ertile Loam y sand 7.0 0.92 0.100 3.3 1.99 0.75 0.24

1 B ray N o .l extractable P.

T h e R h izobium strain IR c 1045 was isolated from leucaena plants growing at Fashola (70 km north o f Ibadan) in southw estern N igeria (Sanginga et a l 1986). T he o ther Rliizobium inoculum , Lx 382, was a single-strain leucaena R hizobium in com m ercial grade granular peat ob tained from N itragin C om pany (M ilwaukee, Wisconsin, USA). In addition to the above trea tm en ts, potassium chloride (50 mg K /k g soil) and zinc sulphate (5 mg Z n /k g soil) were applied in the pots before planting. Seeds w ere inoculated following the m ethod described by V incent (1970); rhizobia num bers were about 107/se e d at planting.

F our kilogram s of the com posite surface soil samples (0-20 cm), passed through a 2 mm sieve, w ere placed in each pot and the respective treatm ent was applied. Leucaena seeds were scarified by nicking the broad end of each seed. Ten seeds of each legum inous tree species w ere p lan ted in each pot. E m ergent seedlings were thinned to five per pot 21 days after p lanting (D A P). Pots w ere w atered daily by weight to bring soil m oisture content to approxim ate field capacity m oisture content. Seedling heights were m easured at 28 and 84 D A P. A t 84 D A P shoots w ere cut at the soil surface and oven-dried (70°C). R oots were cleaned with tap w ater. Nodules w ere picked from the roots, counted, and oven-dried (70°C). P ercen t vesicular arbuscular mycorrhiza (VAM ) infection was estim ated after staining samples

of fine roots with trypan blue (Phillips and H aym an 1970) and using the gridline intersect m ethod. D ried shoots were ground and analyzed for N and P contents. Analysis of variance was conducted on all data sets using the random ized com plete block design. The protected LSD test was used for com parison of means.

R esults an d discussion.

Plant height growth. A t 28 D AP, the height of the plants in the control pots o f both the poor and fertile soils did not differ significantly (Figure 1). A pplication of P to bo th soils increased plant height an average of 20% over that of the no-P treatm ent. Plant height of leucaena fertilized with P increased 26% in both soils while height of gliricidia increased only 15%. This suggests higher requirem ents for P by leucaena. A t 84 D A P height o f leucaena in the control pots of the fertile soils averaged 132% and 156%, with and without P, o f that in the poor soil. In contrast, gliricidia plants in the control pots o f both the fertile and the poor soil exhibited sim ilar height growth. Fertilization with P increased plant height at 84 D A P by about 10% in both soil types, a lower response than that at 28 D AP. This result indicates that the beneficial effect of P on height is lim ited to the early stage of growth. A pplication of N with or without P to the poor soil increased plant height of both species com pared to that obtained in the fertile soil. Fertilizer P can lend tree legumes early vigor and enhance growth. For leucaena, which is slow to establish (Jones and Bray 1983), application of P would be of great advantage.

L E P NPLPEP Poor

Leucaena

T 1 E P NPLPEP Fertile

rfTTTTT L E P NPLPEP C N L'E P NPLPEP

Poor FertileGliricidia

Figure 1. H eight of leucaena an d gliricidia grown in two soils as influenced by N an d P fertilization an d inoculation with two s tra in s of R hizobium .

P lant N a n d sh oo t dry matter. D ry m atter production and N uptake of the two species were higher in the fertile than in the poor soil (Table 2). Shoot dry m atter of gliricidia in the control pots averaged 83% of that of N fertilized plants; unfertilized leucaena also produced 59% of the dry m atter of plants that received urea (Table 3). Phosphorus fertilization increased plant dry m atter yield and N uptake. A ddition of P also im proved the relative effectiveness of symbiosis in som e but not all the treatm ents (data not shown). This param eter was calculated as the ratio betw een N content of plants in the no-N treatm ents with or w ithout rhizobium and that of plants fertilized with N. Phosphorus is known to stim ulate nitrogenase activity (Andrew 1977). T he highest shoot dry m atter increases in both soil types w ere obtained when fertilizer N and P w ere applied simultaneously. The highest plant N yield was obtained in treatm ents

receiving b o th N and P and in those in which the rhizobial inoculants, in particular the N itragin strain , w ere used with fertilizer P. T he local rhizobial strain perform ed well only on gliricidia fertilized w ith P. T he pronounced response in shoot dry m atter and N uptake to P fertilizer on b o th soils, although it underscores the im portance o f P in the legum e-rhizobium symbiosis (A ndrew 1977), also indicates the low P availability of the soil. T he Bray No. 1 extractable P con ten t o f about 3.0 ppm (Table 1) is low and response to fertilizer P can be expected as rep o rted by M oorm an et al. (1975) for similar soils in the zone.

N odu la tion . N odule num bers in the control pots w ere 40% greater in the fertile soil than in the p o o r soil (Figure 2). This difference was probably due to a larger population size of the rh izobia in the fertile soil than in the poor soil. Rhizobia w ere not enum erated in the soils to co rro b o ra te this explanation. Inoculation with the two rhizobium strains increased the num ber o f nodules only for leucaena in the poor soil (Figure 2). N odule num bers on leucaena were h igher fo r plants inoculated with the rhizobium strain from Nitragin than on plants inoculated w ith the local strain. T he indigenous rhizobia may not be the m ost effective particularly for leucaena. In contrast, nodule num bers of gliricidia w ere higher when the local strain was used. G liricidia is known to nodulate freely with native rhizobium strains in a num ber of soils in southw estern N igeria (K ang and M ulongoy 1987), and inoculation may therefore be unnecessary. N itrogen fertilizer applied alone or with P suppressed nodule num bers, possibly due to adverse effect on the legum e-rhizobium symbiotic system.

V A M infection a n d P uptake. For bo th tree species, mycorrhizal infection was high (Table 4). I t averaged 50% for leucaena and 66% for gliricidia in the absence of added P. Gliricidia tended to be m ore infected than leucaena, and the percentage of plants infected was higher in the po o r soil than in the fertile soil. Total P uptake by both tree species was increased only by

T able 2. S hoot weight an d N up take of leucaena an d gliricidia grown in poor an d fertile soils.

T reespecies

Shoot dry weight Poor soil Fertile soil ----- g D M /p la n t------

N uptakePoor soil Fertile soil ----- m g N /p la n t------

L eucaena 3.1 4.2 55.2 90.4G liricidia 4.0 4.5 76.2 97.4LSD (0.05) 0.2 6.4

T able 3. Effect o f N an d P fertilizer and inoculation with two s tra in s of R hizobium on shootd ry weight an d N uptake of Leucaena an d G liricidia.

Soil Shoot dry weight N uptaketrea tm en t P oor soil Fertile soil Poor soil Fertile soil

----- g D M /p la n t------ ----- mg N /p lan t

C ontro l 2.9 3.8 56.4 76.8N 4.9 4.5 88.7 85.7P 3.4 4.4 64.3 95.2NP 5.1, 4.9 93.8 97.7It 2.9 3.8 57.8 77.1IiP 3.4 4.5 68.3 94.0I2 3.1 3.7 69.2 72.3I2P 3.8 4.5 84.4 93.8LSD (0.05) 0.39 12.7

1 phosphorus (NP), local strain of Rhizobium (L), elite strain of Rhizobium (E), and both strains in combination with phosphorus (LP) and (EP).

Figure 2. Effect of N and P fertilizer and inoculation with two strains of R hizobium on nodulation of leucaena and gliricidia grown in two soils.

TabIe 4' m vcnrrhL !! “ fd r and inoculation with two strains of R hizobium on------------m>corrhlzal infection of leucaena and gliricidia grown in two soils.S °d Poor soiltreatm en t Leucaena Gliricidia

%

Fertile soilLeucaena Gliricidia

ControlNLEPN PLPE PLSD (0,05)

68.163.852.652.724.0 18.6 45.626.1

71.063.075.267.2 59.6 43.957.263.0

39.6 66.947.424.5 37.0 24.217.719.8

23.1

59.158.1 59.7 72.956.550.559.2 51.0

m . ttXESSSl ^phosphorus (LP) and (EP). ’ nd strauls m combination with

application of P fertilizer and differed with soil fertility status (Table 5) O n the poor soil

l e a s e d o X CW 2 d 'mCK? Xf bTy 14l9% 1111(1 154% whiIe on the fertile sod it was increased only 78% and 105%, respectively. In the control treatm ent, gliricidia had higher Pcontent in the tissue than leucaena. This result may be due to the greater propensity of gliricidia to associate with VAM (Kang and M ulongoy 1987). P P y

Conclusion. T he study has revealed that low N and P are, in part responsible for the n n n r establishm ent of the two tree species in Alfisols o f southw estern Nigeria. Fertilizer N appliedn a p ° f ^ th P m thC ? ° ° r SoU lncreased Plant height, shoot dry m atter and N c o n te n t^ 84 D A P o f the trees to the sam e level as in the fertile soil th a tr e c e iv e d ^ o f e r t f a The pronounced positive response to N fertilizer in both soils indicates that the symbToTes with indigenous rhizobia was not very effective, particularly for leucaena. Inoculation with the two

T able 5. Effect o f N an d P fertilizer and inoculation with two s tra in s of Rhizobium on Pup take of leucaena an d gliricidia grown in two soils.

Soiltrea tm en t3 L eucaena

P oor soilGliricidia

mg P /p lan t -

Fertile soil Leucaena Gliricidia

C ontrol 2.1 3.4 2.8 3.8N 2.6 3.4 2.9 4.0L 1.9 3.1 2.5 3.4E 1.9 3.7 2.8 3.7P 5.1 8.4 4.6 8.6N P 5.8 7.4 5.2 6.9LP 5.5 9.6 4.7 7.5E P 4.6 9.1 5.1 7.5LSD (0.05) 1.0

a The various treatments tested were nitrogen only (N), phosphorus (NP), local strain of Rhizobium (L), elite strain of Rhizobium (E ), and both strains in combination with phosphorus (LP) and (EP).

strains o f rhizobium , although it im proved shoot dry m atter and N uptake occasionally, was not as effective as the use of fertilizer N. It is necessary to identify m ore effective strains of rh izobium for these environm ents. Application of fertilizer P may be necessary to ensure p ro p er nodulation, N 2 fixation, and tree growth.

A cknowledgem ents. T he authors thank Ms. B.T. Owoaje for technical assistance, M r. B ernard O nugw u for w ord processing, and M r. S.O. A dediran for statistical analysis.

References:

A ndrew , C.S. 1977. N utritional restrain ts on legume - symbiosis. In J.M . Vincent, A.S. W hitney and J. Bose (eds), Exploiting the Legume-Symbiosis in Tropical A griculture. College of Agric. M isc. Publ. No. 145. Univ. Hawaii, H onolulu, H I. p. 251-274.

C obbina J., B.T. Kang, and A .N . A tta-K rah. 1988. Effect of soil fertility on early growth of leucaena and gliricidia in alley farms. A groforestry Systems (in press).

Jones, R J . and R A . Bray. 1983. A gronom ic research in the developm ent of Leucaena as a p astu re legum e in A ustralia. In Leucaena R esearch in the A sian - Pacific R egion, p. 41-48. ID R C , Ottawa, C anada.

Kang, B.T. and K. M ulongoy. 1987. Gliricidia sepium as a source of green m anure in an alley cropping system. In G liricidia sepium (Jacq) Walp: M anagem ent and im provem ent. N itrogen Fixing T ree A ssociation Special Publ. 87-01. NFTA, W aim analo, H I. p. 44-49.

Kang, B.T., G .F. W ilson, and T.L. Lawson. 1984. Alley cropping: A stable alternative to shifting cultivation. IITA , Ibadan, N igeria. 23 p.

M oorm an , F .R ., R . Lai, and A .S.R . Juo. 1975. T he soils o f IITA. Tech. Bull. International Institu te of Tropical A griculture, Ibadan, Nigeria. 48 p.

Phillips, J.M . and D.S. H aym an. 1970. Im proved procedures for clearing roots and staining parasitic and vesicular arbuscular mycorrhizal fungi for rapid assessm ent of infection. Trans. B rit. Mycol. Soc. 55:158-161.

Sanginga, N., K. M ulongoy, and A. Ayanaba. 1986. Inoculation of Leucaena leucocephala (L am .) de W it with R hizobium and its nitrogen contribution to a subsequent m aize crop. Biol. Agric. H ortic . 3:347-352.

V incent, J.M . 1970. A m anual for the practical study of root-nodule bacteria. IBP H andbook N o. 15. Blackwell Scientific Publications, Oxford. 164 p.