Grain Legumes and Green Manures for Soil Fertility in ... - cimmyt

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• Assessment of the potential benefits from the _input of fixed N2, residual effects on subsequent crops following the growth of legumes or effects on crops associated withlegu!11es. Need for a Reference Crop: -The assumption is that both non-fixing (control) .and fixing crops take up N from the soil in the same ratio. -Wrong choice of a.reference crop can either underestimate or overestimate the N2 fixed. • Reference crop combinations include wheat (bean), maize (soyabean), and non-promiscuous soyabean variety (soya bean). Why do legumes fix nitrogen?: • "Conventional wisdom" has it that legumes fix N for themselves. • However data here showed thaf maize yields after soya bean increased even where stover was removed. This appeared due to root exudates and build-up in SOM. Inoculum Use: The following aspects are important: 1. Isolate 2. Selection and authentication (Testing) 3. Production for specific locations The possibility exists that applying exotic strains of rhizobium indiscriminately can suppress indige~ nous strains. Effect of N source on Bean grain yield: • CIAT 899 and the local isolate were comparable in Mbala and Lundazi, Zambia. • In Pembela, the native rhizobia strains at the trial site were as effective as other strains in increasing grain yields. • Soil available P determines to a large degree the nodulation in groundnut in semi-arid parts of Zimbabwe. • Enhancing AMF activity of native fungi promotes nodulation and increases shoot N concentration in lab lab bean. • To enhance N fixation, can we explore combinations of P and Rhizobia? Screening of Annual Legumes for Adaptation and Use Presentations covered indigenous herbaceous legumes, timing of legum~ incorporation, performance of short duration pigeon pea, risk diversification through legumes and simulating maize response to mucuna. Three of the five papers were directly devoted to screening. The other two dealt with issues relevant to screening. Only the paper on indifallows dealt with bringing on stream a new family of legumesthe indigenous ones . Indifallows: • These appear to be self-regenerating and well adapted. • Among the benefits for N2fixation andfarmer adoption, some indifallow species demonstrated high levels of N2 fixation, and the "Gwezu smell approach" participatory method for identifying legumes works well. • There was some concern that these species may not withstand grazing. • Suggestions .for the indifallow work included extending the study to Matebeleland and measuring how the population of species varies with the duration of the fallow. It is likely to change markedly. Effect of time of legume incorporation on maize yield: • Yields from early or late incorporation were not statistically different. Late incorporation spreads labour demand. This is consistent with the earlier SoilFertNet study over three seasons. • Soil moisture content from late incorporation is higher. • Water use efficiency is an additional benefit to N2-fixation. Inclusion of water use in the study objectives was commended. • Mucuna and C. grahamiana are recommended as best bets for Zimbabwe communal lands. C. grahamitma adapts better to degraded soils due to its strong roots. • Examine the method of incorporation-it might be a constraint for expansion of plot sizes. Short duration pigeonpea in Matebeleland: • The short duration types performed better in clayey than in sandier soils. • Concern was raised about the low yields and competition by weeds. • Also there was concern about the need for spraying against pests. Explore the effect of not spraying on performance. • The recommended time of incorporation is after harvesting the grain. • We also need to see how to improve access to literature about past work on legumes in the region. 240 Grain legumes and Green Manures for Soil Fertility in Southern Afriea
Screening: • New options identified were "indifallows" and a broadening of the suitability range for pigeon pea in southern Africa. • All three screening studies reported were started recently in the 2000/01 and 2001/02 seasons, yet benefits usually accrue after 3-5 years. Computer simulation of benefits could augment the experiments. • There was a general view that weshould continue screening but that first we should establish what has already been done by a thorough literature review and employing tools such as the Legume Expert System. • Biotechnology offers prospects of improving our ability to screen thousands of species. Risk diversification and computer simulation: • Adoption of legumes depends on return on investment and risk characteristics. • Computer simulation is undertaken to explore long-term trends. • The results (recommendations) from the APSIM simulations are consistent with current farmer practices except for the use of kraal manure in drier areas. • The extremely low rates of fertilizer application in serni-arid areas (18 kg/ha) reflect farmer aversion to risk in these areas. • Non-market benefits (remaining in the soil) are captured in the yield through APSIM. Values not captured are considered not relevant to farmers. Simulating maize yield response: • Computer simulation is undertaken to overcome the short-term perspective of most expetimental trials. The simulations reported covered a 46-year period. • APSIM, unlike many modeling tools, considers carry-over effects of variables including soil N. • Long-term simulation of Mucuna indicates large potential benefits over the long term. Increases of 100-200% in maize yield were reported. These benefits are not captured in short-term experiments. • So far, the simulated maize yields are showing satisfactory agreement 'with field trials, but more needs to be done about legumes. Consultations are underway to validate legume grain yields. General comments: We should look at soil fertility more broadly and give greater attention to other benefits from leg umes besides N-fixation, e.g. soil physical proper ties, water use efficiency, weed suppression and till- age effects. For example, pigeon pea's noted contribution to SOM is probably traceable to deep rooting, while chickpea increases the availability of P. With respect to soil nutrients, whereas P and N are adequately discussed; more consideration should be given to other nutrients such as zinc. A general question was, where should we start the screening; from the plant side or the rhizobium side? It is important that improved legume varieties be developed. This means that we need to involve/ collaborate with breeders in the screening. We also need to be involved in their work so that the soil fertility improvement, water use, weed suppression and other traits that we would like to see enhanced in legumes are given some attention by breeders. Identification of Best Bet Legumes for On-Farm Performance as Grain Legumes, Intercrops, Rotations, and Green Manures Eight papers and one poster were presented. Key findings from the presentations and discussion: • From the evidence presented in the different papers, it is clear that yield responses were greater when crop residues and manures were ploughed in, i.e. incorporated, compared to · when they were left on the surface as a mulch. Consequently, we may begin to see some conflicts between soil fertility and conservation farming which advocates that crop residues be left on the soil surface as a mulch. • Intercropping vs. rotation issues. Data presented by the authors suggest that in the short term (two or three seasons) a cereal-green manure rotation is less productive than a cereal/ grain legume intercrop. This is supported by the fact that many farmers that have participated in trials are more willing to adopt an intercrop approach to soil fertility amendment than a green manure-cereal rotation, particularly when land is scarce. • We had little information presented on the intercropping characteristics of the different legume and cereal varieties currently available. More work needs to be done on that. • Although many of the studies reported in this session were conducted on farmers fields, very Grain legumes and Green Manures for SQil Fertility in Southern Africa 241
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Grain Legumes and Green Manures for
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Acknowledgments • The Leopard Roc
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Evall!ating mucuna green manure tec
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INTRODUCTION AND CONFERENCE OBJECTI
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Table 1. Paradigm shifts underlying
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100 90 80 - - 0 - - Uptake by ihe m
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- 6 ~ 9 8 7 0- 5 CḎ ns 4 0::: 3
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Table 3. Millet grain and total dry
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Dvorak KA 1996. Adoption potential
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LEGUMES FOR SOIL FERTILITY IN SOUTH
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to the system in such a way that th
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Muetzelfeldt, R.1. 1995. A framewor
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ing capacity. Legumes offer other b
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people/km2), land holdings are smal
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ments. It would help researchers to
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Own livestock Gununo farmers for th
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Questions and Answers ~ey Papers To
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Historical Perspective on Soyabean
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ganic amendment for resource-poor f
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MPhil. Thesis. University of Zimbab
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deal of research work has been bias
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1600 '7 ns 1400 ~ 1200 Cl ~ 1000 "C
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Arbuscular mycorrhizal fungi (AMF)
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Boswell EP, Koide RT, Shumway DL, A
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Materials and Methods The trial was
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0.9 0.8 ~ 0.7 Rec '-' 0.6 Vl ::9 0.
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Series no 5. Soil Science SOciety o
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Materials and Methods Persistence o
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content resulted in increased rhizo
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(Mugwiia and Murwira, 1997). Howeve
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Table 2. Average maize yield estima
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implied that most fanners prefer to
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] Questions and Answers Rhizobium,
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ADDING A NEW DIMENSION TO THE IMPRO
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Materials and Methods The study use
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a) Chikwaka b) Chinyika !21 C. absu
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Table 3. N, P and Kconcentrations (
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Abstract SCREENING OF SHORT DURATIO
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Table 2. Characteristics of short d
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RISK DIVERSIFICATION OPPORTUNITIES
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management technologies with differ
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Table 3. Expected annual returns (Z
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Table 6. Risk diversification indic
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een renewed interest in green manur
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unfertilised maize crop of over 200
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Questions and Answers Screening of
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GREEN MANURE AND FOOD LEGUMES RESEA
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7000 6000 ';' €.. 5000 .~MzSole :
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Table 5. Maize grain yield (kg ha")
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Phiri, A.D.K. 1999. Effects of Sesb
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amount of roots with sl:nnhemp. It
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It was proved that a mixed farming
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Table 3. Above·ground biomass (t/h
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and horticulture in Zimbabwe: Case
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GRAIN LEGUMES AND GREEN MANURES IN
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Results Table 1. Adaptation of gree
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Four rates of fertilizer N were app
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THE ROLE OF COWPEA (VIGNA UNGUICULA
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Table 1. Non-legume cropping patter
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Table 9. Common pests on cowpeas as
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few of the farmers interviewed acqu
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Murwira, H.K., M.J. Swift and P.G.H
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Materials and Methods On farm exper
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18000 1600) 14000 a) Zambia 12000 m
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EFFECT OF DIFFERENT GREEN MANURE LE
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.. ~ Table 2. The effect of time o
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Chivinge, O.A., E. Kasembe, and I.K
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times with regionally specific adap
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ter content at 180 cm was still wel
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to amount of biomass, quality of bi
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with the natural fallow, which did
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and K to maize as an equivalent amo
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forts to understand the mechanisms
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gen recovery rates in relation to p
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The first steps to improve soil fer
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Questions and Answers .Identificat
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MUCUNA - MAIZE ROTATIONS AND SHORT
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Table 3. Percent nitrogen (% N) con
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~e decomposition of legume residues
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Table 3. Effect of forage legumes o
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available nutrients and vice versa,
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Conclusion and Recommendation Mucun
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Specific objectives were to: • Te
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'"~ v '" ~ ~ 1400000 1200000 100000
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EFFECT OF SURFACE APPLICATION AND I
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it 4 a···· · ... - :.!! e.....
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PERFORMANCE OF GREEN MANURES AND GR
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Mungwi soil, cowpea and soyabean pr
Page 198 and 199: Among BNF systems, symbiotic system
Page 200 and 201: 3500 .f"'3000 ca ,c2500 CI "" - 200
Page 202 and 203: above-ground biomass was not transl
Page 204 and 205: 3000 "0 ]i >. ,5 ~ C> 800 600 400 2
Page 206 and 207: Most interventions involving green
Page 208 and 209: ~ ~~----.-~r-~-------------r~~ Aoo
Page 210 and 211: stover N, followed by after pigeon
Page 212 and 213: tems in Malawi and Zimbabwe. Procee
Page 214 and 215: 1965). The tailings and AgLi were a
Page 216 and 217: The significant soybean yield could
Page 218 and 219: twice the yield is necessary. We ha
Page 220 and 221: Table 1. Maize and Grain Legumes Pr
Page 222 and 223: Recommendations and Conclusion In v
Page 224 and 225: performance of private sector compa
Page 226 and 227: the investment costs incurred. The
Page 228 and 229: Results and Planning Workshop. Soil
Page 231 and 232: A SOCIO-ECONOMIC ANALYSIS OF LEGUME
Page 233 and 234: Table 1. Gross margins from the dif
Page 235 and 236: Abstract LINKING TECHNOLOGY DEVELOP
Page 237 and 238: 3. If households are linked to prod
Page 239 and 240: Table 9. Average Table 8. Pigeonpea
Page 241 and 242: ance of sorghum-pigeonpea intercrop
Page 243: Mligo, J.K., 1995. Pigeonpea breedi
Page 246 and 247: To Charles Nhemachena, et al. Q: 1)
Page 250 and 251: few studies characterized the house
Page 252 and 253: • Conduct more research to measur
Page 254: Socio-Economics, Policy and Technol
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