Tropical and International Agriculture-BSC SS2012

Lecture 7 – 15.05.12Prof. Dr. Anthony Whitbread (awhitbr@gwdg.de)

Crop Production Systems in the TropicsGrisebachstr. 6, 37077 Göttingen, Germany

Lectures on tropical crop production systems found:http://www.uni-goettingen.de/de/354727.html

Pulses and their use in tropical farming systems

Outline of lecture• Introduce systems where pulses are used.• Outline the multiple roles of pulses in the system:

– Uses and why farmers use them– N fixation and nodulation– Planting methods and soil nutritional requirements

• Introduce some of the most common pulse species– Cowpea– Soybean– Peanut

Crops and Production Systems in the Tropics

Classification of Tropical Farming Systems*

-where annual crops are a dominant/important component

1. Shifting cultivation systems2. Semi-intensive rainfed systems3. Intensive rainfed systems4. Irrigated and flooded systems5. Mixed annual/perennial systems

Examples of possible intensification in the context of resource poor farmers (examples from semi-arid sub-Saharan systems):a. Micro-dosing (top-dressing small amounts of N)b. Conservation agriculture (CA)c. Cash crops (Pulses) especially in #3d. Integrated soil fertility managemente. Crop livestock systemsf. Agroforestry and Energy crops (covered by Dr Worbes)*Norman M.J.T. (1979). Annual Cropping Systems in the Tropics. Gainesville, Florida: University Presses of Florida, 276 pp.

Cropping frequency increases

Pulses in farming systemsHow and why smallholder farmers in the tropics utilise pulses

What are pulses?Alternative names: grain legumes (Hülsenfrucht-Deutsch),

Life cycle: Perennial• > 2 years – many years. Annual• < 1 year or 1 season – germinates, vegetatively grows, flowers and

dies.Biennial< 2 years or 2 season – germinates, vegetatively grows, often flowering and fruiting in year 2 and then dying.

Method of propagation:Usually sown, annually, inoculated with rhizobium, some additional fertiliser (no or low N, but other nutrients as necessary- often P and Mo are required)

Meeting human nutritional needs:• Pulses play an important role in providing a protein rich source of food,

particularly where meat is not common e.g. Southern India.• Supply essential amino acids (esp. Lysine) not in sufficient quantities in staple

cereals.• Globally (1990 figures), plant derived protein supplies about 70% of human

intake – although rapid changes in dietary consumption is changing this.• Examples of the most important pulses:

Pulses supplying seed/mealPigeonpea – Cajanus cajan (L.) Millsp.Chickpea – Cicer arietinum (L.) (Desi and Kabulis types)Lentil – Lens culinaris Medik (native to Middle East)Cowpeas – Vigna unguiculata (L.) Walp.French/Haricot bean or Phaseolus spp. – P. vulgaris L.

Pulses as oilseed crops (but may also supply seed/meal)Bambara groundnut – Vigna subterranea (L.) Verdc.Peanut – Arachis hypogaea (L.)Soybean – Glycine max (L.) Merr.

Source: Kamanga et al. (2009). African Journal of Agricultural Research Vol. 5(8), pp. 668-680.

Special requirements of grain legumesNodulation: Specific rhizobial strains Vs promiscuous legume varieties

The term rhizobia includes the genera –Rhizobium, Bradyrhizobium, Sinorhizobium and several other minor groups.

Inoculation: involves obtaining a fresh and species appropriate strain, coating the seed and planting into good soil conditions that favour survival of the rhizobia.

http://vimeo.com/13293944 (from 3.36 min)

Figure 6: Differences in nodule numbers between a wild type soybean plant (left), where the plantcontrols the number of nodules to the minimum necessary to sustain its nitrogen needs, and asupernodulation mutant (right), in which the plant has lost the ability to control nodule numbers -the roots are “supernodulated” by rhizobia. Photo courtesy of Prof. Peter Gresshoff, University of Queensland and sourced from: http://www.cilr.uq.edu.au/UserImages/File/Nodulation%20and%20Nitrogen%20Fixation%20Workshop.pdf

Some characteristics of nodulation tropical grain legumes.

Source: Giller (2006). Nitrogen Fixation in Tropical Cropping Systems. 2nd Edition, CABI Publishing. p.142.

• Plant roots exude flavonoids to stimulate rhizobia in the soil to move towards the roots.

• Rhizobia infect the root hairs, and multiply inside of the infection thread. Plant cortex cells divide to form the nodule.

• Autoregulation is a plant mechanism to control nodule numbers

N Fixation• N fixation in Southern Australia in the range of 20-25 kg N/t

dry matter (regardless of species, soil type and environment).• N fixation is highly dependent on soil nitrate level• Not always a net contribution of N

� -41 to +135 kg N/ha for lupin� -32 to +96 kg N/ha for peas

• A high nitrogen harvesting Index (NHI) is likely for most grain legumes under commercial production

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100

S oil n itra te (kg/ha)

%N

dfa

m ungbeansira trolucernelab lab

R 2 = 0 .54

Special requirements of grain legumesNodulation: Specific rhizobial strains Vs promiscuous legume varieties

The term rhizobia includes the genera –Rhizobium, Bradyrhizobium, Sinorhizobium and several other minor groups.

Inoculation: involves obtaining a fresh and species appropriate strain, coating the seed and planting into good soil conditions that favour survival of the rhizobia.

Soil nutrition: In the tropics, highly weathered, leached, nutrient poor soils are common. Acid soils, particularly common in the tropics (e.g. Oxisols, Ultisols, some Alfisols), have usually low available phosphorus, may strongly fix P, and have toxic concentrations of Aluminium and Manganese.

Nutrient toxicity/deficiency and pH

Impacts

Source: Constraints to cropping soils in the northern grains region-a decision tree” GRDC Northern SSC program (Qld NR&W publication)

pH Water 1:5

Planting methods: In traditional farming (esp. African), intercropping is the most common practice, but relay planting and rotation is more usual for the commercial farmer.

Intercropping: having more than 1 species planted simultaneously (poly-culture). Reasons include:Tradition, risk management, potential for higher production/ha, complementarity of crop types, low plant populations of each spp. (low planting rate &/or poor seed quality).

Relay planting, a form of intercropping: involves 2 planting times with the 1st crop (usually the staple, e.g. maize) planted on wide rows and the 2nd crop planted later to reduce competition.

Crop sequences (rotation): planting a single crop spp. (monoculture), on an area of land –soil type, fertility, insects, weeds and disease pressure will influence the need for rotation of sequence of spp.

Capturing the benefits of legume rotations• Under rainfed conditions, especially in semi-arid regions,

capturing the benefits of the ‘legume’ phase (forage, pulse, green manure) in subsequent crops depends on many factors:– How and when the legume crop is terminated.– Building up soil water pre-sowing (decreases risk of crop failure)– Maintaining the soil organic matter & structural benefits of the ley

(N losses)• Our approach to these complex issues is via modelling and field

experimentation– 2 SIA courses cover these aspects:*Experimental Methods in Tropical Agronomy (P19M)*Crop Modelling for Risk Management (P16M)

Cowpea - Vigna unguiculata (L.) Walp.

• Probably centre of origin, West Africa.• Grown extensively as a subsistence crop: vegetable (pods, flowers), seed,

cut and carry forage.• Amongst the most drought tolerant of herbaceous tropical legumes.• In Africa ‘bunch’ (grain) and ‘spreading’ (dual purpose) types.

Factsheet:http://www.tropicalforages.info/key/Forages/Media/Html/Vigna_unguiculata.htmhttp://www.uni-goettingen.de/en/technical-bulletins-for-limpopo-province-south-africa/305574.html

Soybean – Glycine max (L.) Merr. (Rehm&Espig p.94-97)• Cultivated in China since ancient times, native to East Asia.• Provides 35% of the worlds protein requirements – much of which is fed to

animals to produce animal protein.• In the USA, 2nd most valuable crops and occupies ~15% arable land.• Immature pods used as vegetables, seed used for soy sauce, cooking oil,

soybean milk, protein for curd/tofu….85% processed into meal and oil.• Many believe soybeans to be a source of complete protein and to enhance

human health.

Soybean – Glycine max (L.) Merr. (Rehm&Espig p.94-97)

• Small erect branching annual.• Growth duration 90-110 days (some 140 days)• Photoperiod sensitive – sensitive to short daylength with duration of

vegetation growth, induction of flowering, length of flowering, pod filling, related to photoperiod.

• Self pollinated

• Examples of systems• Brazil – Rio grande do Sul: double crop summer soybean /winter wheat• Argentina: summer cropping only, soybean- maize rotation.• SE Asia: rotation with wet rice in intensive systems (some tolerance of

poor aeration.

Soybean – Glycine max (L.) Merr.

• The US, Brazil, Argentina and China are the largest producers (216 million t produced in 2007 from 93 m ha). Only the last 35 years has soybean been cultivated in South America

• Genetically modified soybean – Monsanto introduced Roundup Ready soybean in 1995. In the US 93% of soybeans are GM.

• Roundup is used for weed control and its use in RR soybeans reduced the use of more harmful herbicides.

• In 2010, the soybean genome was sequenced.• In Argentina, soybean covers half of the pampas, with production on about

13.5 m ha (2011) – In 2009 the export trade was $3.2 b, half for China.• There are polarised views on the success or otherwise of soybeans in

Argentina and other parts of South America, especially in regards to impacts on the environment (e.g. Amazon).

Peanut – Arachis hypogaea (L.) (Rehm&Espig p.97-101)

• Also known as groundnuts, earthnuts (Note. Bambara groundnuts is a different spp.)

• Centre of origin probably NW Argentina and S.Bolivia + sub-spp. from Brazil.• Now also a major crop in W. Africa, India and USA.• Widely cultivated as a marginal crop (low yielding).

• Features: production of subterranean fruit. After anthesis, the ovary elongates and forms a peg which enters the soil 5-10 days later. This peg is where the pod and seed (nut) forms.

Fig. 25 from Rehm&Espig. Arachis hypogaea. Carpophores entering the soil (schematically). F1 = dried flower, Fr = fruit

Crops and Production Systems in the Tropics

Extra reading

1. For resource use concepts and agronomic principles:Azam-Ali, S.N, Squire, G.R., (2002). Principles of Tropical Agronomy. CABI, Wallingford, UK. 236 pp.

2. For cultivation, economic value and utilisation of plants:Rehm, S. and Espig, G. (1991). The cultivated Plants of the Tropics and Subtropics. Verlag josef margraf. 552 pp.Available from http://www.uni-goettingen.de/en/209930.html

3. For introduction to systems and major tropical food crops:Norman M.J.T. (1979). Annual Cropping Systems in the Tropics. Gainesville, Florida: University Presses of Florida, 276 pp.

4. For N fixation and legumes in cropping systems:Giller, K.E. (2006). Nitrogen Fixation in Tropical Cropping Systems. 2nd Edition, CABI Publishing.*