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

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content resulted in increased rhizobial populations. Chatel and Parker (1972) noted that heavy textured soils formed micro aggregates, which afforded some protection to rhizobia against high temperatures. Rhizobia also survive saprophytically in the absence of a legume host, therefore organic carbon is an essential source of energy required for their growth and survival. The rhizobial strain MAR 1491 was found in most inoculated field soils since it is the most widely used strain in soyabean inoculant production in Zimbabwe. In some soils, the strain MAR 1495 was also found because it was once used in combination with MAR 1491 during inoculant production. The uninoculated field controls had none of the tested strains because they have no history of rhizobial inoculation. Conclusion and Recommendations Rhizobial inoculant strains survive in smallholder field environments for at least three seasons, so reinoculation of previously inoculated fields is not beneficial to the farmer. Inoculation when introducing a soyabean crop in a new area for the first time is essential. Thereafter, a second soyabean crop grown after rotation with a cereal does not require inoculation since a significant population of rhizobia will still be present in the soil. Rhizobial survival can be further enhanced by raising soil pH and organic matter content and in soils with high clay amount. Re-inoculation may therefore need to be more frequent in sandy soils. Acknowledgements The Rockefeller Foundation for funding the project. Also the farmers, project assistants and the Soil Science Department of the University of Zimbabwe. References Chatel, D.L and Parker, c.A. 1972. Survival of field grown rhizobia over the dry summer period in western Australia. Soil Biol. Biochem. 5:415-423. Kasasa P., 1999. Biological nitrogen fixation by promiscuous nodulating soyabean Glycine max [L] Merr) varieties in communal soils of Zimbabwe. MPhii Thesis. University of Zimbabwe, Harare, Zimbabwe, pp 37-41. Mapfumo, P. 2000. Potential contributions of legumes to soil fertility management in sIPallholder systems of Zimbabwe: the case of pigeon pea (Cajam!s cajan [L] Millsp.). DPhii Thesis. University of Zimbabwe, Harare. Zimbabwe, pp 62-64. Mpepereki, Sand Makonese F. 1995. Prevalence of cowpea and soyabean rhizobia in field soils of Zimbabwe. Zimbabwe Journal of Agriculture 33:191-205. Mpepereki S., Javaheri F., Davis P. and Giller K.E. 1999. Soyabean and sustainable agriculture. Promiscuous soyabeans in southern Africa. Field Crop Research 65:137-149. Rusike J., Sukume c., Dorward A., Mpepereki S. and Giller K. E. 2000. The economic potential of soyabean production in Zimbabwe. Soil Fert Net Special Publication. Harare, Zimbabwe, pp 1-3. Tattersfield, J.R. 1996. Soyabean Production and Research in Zimbabwe. Seed Co-op Company of Zimbabwe, Harare, Zimbabwe. 56 Grain Legumes and Green Manures for Soil Fertility in Southern Africa
INTEGRATING ORGANIC RESOURCE QUALITY AND FARMER MANAGE MENT PRACTICES TO SUSTAIN SOIL PRODUCTIVITY IN ZIMBABWE Abstract FLORENCE MTAMBANENGWE and PAUL MAPFUMO Department of Soil Science and Agricultural Engineering, University of Zimbabwe, P. O. Box MP 167 Mt Pleasant, Harare, Zimbabwe Maintenance of soil fertility on smallholder farms in Southern Africa is almost entirely dependant on locally available organic resources, with mineral fertilizers only dominating in exceptional cases for relatively wealthy fc:nners. The exploitation of nitrogen-fixing legumes for soil fertility purposes, be it in the form of residues from grain or green manure legumes, is not widespread in Zimbabwe smallholder farming systems .. In a newly initiated study in three agroecological regions in Zimbabwe, we focus on the differential effects oforganic resource quality and quantity on the manifestation of soil fertility gradients and subsequently on crop yields as influenced by fanner management practices. Both Master/Innovator farmers and poor farmers are targeted in the exploration of the within1arm soil fertility gradients (usually giving rise to high yielding 'rich' and low yielding 'poor' fields) observed under different management regimes. Preliminary results showed that mineral fertilizer was the most common nutrient source used by over 85% of the fanners from three identified farmer groups (Class A - Master farmers, Class B -. Innovator fanners and Class C - Resource poor farmers). Livestock manure and woodland litter featured as common organic nutrient sources in Zimuto, while in Chinyika and Chikwaka, less than 50% of the farmers used these as additional nutrient sources. As a result of frequent organic nutri~nt source usage, soil organic carbon contents of the rich and poor fields of Zimuto was significantly higher than from the other two agro-ecological regions (p < 0.05) with values reaching 11.5 mg C g-l soil (rich field) and 8.5 mg C g.l soil (poor field) . The bulk of the tested soil had very little total nitrogen « 1 mg Ng-l soil). Although the chances of building soil organic matter (SOM) under granitic sands in Zimbabwe are slim, understanding the influence of organic resource management on SOM dynamics, short-term N availability and mineral fertilizer use efficiency is critically important. Target farm sites serve to complement long-term experiments in explaining the interaction between organic resource management and crop yields. In addition to these preliminary results, the principles and approaches of the study are also discussed in this paper. Key words: Organic resource quality, soil organiC matte~, mineral fertilizer Introduction Marked differences in soil fertility levels and nutrient balances can often be observed for the different fields within one smallholder farm. These withinfarm soil fertility gradients have a major impact on overall farm productivity, yet their dynamics are often poorly understood. Several reasons could be attributed to this high variability, although inherent soil properties, micro-climatic conditions and farmer management practices may be obvious determining factors (Mapfumo and Giller; ~001; Sanchez and Jama, 2002; ·Smaling et aI., 1997). Farmer management of fields varies with time of planting, type of crop planted, type and quality of added inputs (including access to cash for purchasing inputs) and the efficiency with which nutrients are used. Most smallholder farmers in Zimbabwe recognize the importance of soil fertility and its conservation. There is also general knowledge among both scientists and farmers that the application of organic residues improves the physical conditions of soil, although infonnation as to why this happens is still often very limited (Sanchez etal., 1989; Palm et aI., 1998). Agricultural activities and maintenance of soil fertility in a smallholder farming commUnity is almost entirely dependant on locally available resources. However, given the present scenario where traditional strategies for sustaining soil and crop productivity have been outpaced by the growing human population, a diminishing natural resources base, and the downward spiral of many national economies, the question of resource availability has become topical. The big question is: what options are available to the smallholder fanner for soil amelioration? Annual woodland litterfall may be as much as 5 t ha- l and measured annual litter collections in Masvingo, southern Zimbabwe, by Nyathi and Campbell (1993), ranged from 0.2 to 1.2 tonnes per household. In reality, most communal areas are in a severe ~tate of deforestation. Livestock manure, cattle manure in particular, is a traditional source of plant nutrients and can be one of the cheapest sources of organic fertilizer in many smallholder communities Grain legumes and Green Manures for Soil Fertility in Southern Africa 57
Page 2 and 3:
Grain Legumes and Green Manures for
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Acknowledgments • The Leopard Roc
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Evall!ating mucuna green manure tec
Page 9:
INTRODUCTION AND CONFERENCE OBJECTI
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Table 1. Paradigm shifts underlying
Page 14 and 15: 100 90 80 - - 0 - - Uptake by ihe m
Page 16 and 17: - 6 ~ 9 8 7 0- 5 CḎ ns 4 0::: 3
Page 18 and 19: Table 3. Millet grain and total dry
Page 20 and 21: Dvorak KA 1996. Adoption potential
Page 23 and 24: LEGUMES FOR SOIL FERTILITY IN SOUTH
Page 25 and 26: to the system in such a way that th
Page 27: Muetzelfeldt, R.1. 1995. A framewor
Page 30 and 31: ing capacity. Legumes offer other b
Page 32 and 33: people/km2), land holdings are smal
Page 34 and 35: ments. It would help researchers to
Page 36 and 37: Own livestock Gununo farmers for th
Page 39: Questions and Answers ~ey Papers To
Page 42 and 43: Historical Perspective on Soyabean
Page 44 and 45: ganic amendment for resource-poor f
Page 46 and 47: MPhil. Thesis. University of Zimbab
Page 48 and 49: deal of research work has been bias
Page 50 and 51: 1600 '7 ns 1400 ~ 1200 Cl ~ 1000 "C
Page 52 and 53: Arbuscular mycorrhizal fungi (AMF)
Page 54 and 55: Boswell EP, Koide RT, Shumway DL, A
Page 56 and 57: Materials and Methods The trial was
Page 58 and 59: 0.9 0.8 ~ 0.7 Rec '-' 0.6 Vl ::9 0.
Page 60 and 61: Series no 5. Soil Science SOciety o
Page 62 and 63: Materials and Methods Persistence o
Page 66 and 67: (Mugwiia and Murwira, 1997). Howeve
Page 68 and 69: Table 2. Average maize yield estima
Page 70 and 71: implied that most fanners prefer to
Page 73 and 74: ] Questions and Answers Rhizobium,
Page 75 and 76: ADDING A NEW DIMENSION TO THE IMPRO
Page 77 and 78: Materials and Methods The study use
Page 79 and 80: a) Chikwaka b) Chinyika !21 C. absu
Page 81 and 82: Table 3. N, P and Kconcentrations (
Page 83 and 84: Abstract SCREENING OF SHORT DURATIO
Page 85 and 86: Table 2. Characteristics of short d
Page 87 and 88: RISK DIVERSIFICATION OPPORTUNITIES
Page 89 and 90: management technologies with differ
Page 91 and 92: Table 3. Expected annual returns (Z
Page 93: Table 6. Risk diversification indic
Page 96 and 97: een renewed interest in green manur
Page 98 and 99: unfertilised maize crop of over 200
Page 101 and 102: Questions and Answers Screening of
Page 103 and 104: GREEN MANURE AND FOOD LEGUMES RESEA
Page 105 and 106: 7000 6000 ';' €.. 5000 .~MzSole :
Page 107 and 108: Table 5. Maize grain yield (kg ha")
Page 109: Phiri, A.D.K. 1999. Effects of Sesb
Page 112 and 113: amount of roots with sl:nnhemp. It
Page 114 and 115:
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
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Among BNF systems, symbiotic system
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3500 .f"'3000 ca ,c2500 CI "" - 200
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above-ground biomass was not transl
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3000 "0 ]i >. ,5 ~ C> 800 600 400 2
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Most interventions involving green
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~ ~~----.-~r-~-------------r~~ Aoo
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stover N, followed by after pigeon
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tems in Malawi and Zimbabwe. Procee
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1965). The tailings and AgLi were a
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The significant soybean yield could
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twice the yield is necessary. We ha
Page 220 and 221:
Table 1. Maize and Grain Legumes Pr
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Recommendations and Conclusion In v
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performance of private sector compa
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the investment costs incurred. The
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Results and Planning Workshop. Soil
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A SOCIO-ECONOMIC ANALYSIS OF LEGUME
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Table 1. Gross margins from the dif
Page 235 and 236:
Abstract LINKING TECHNOLOGY DEVELOP
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3. If households are linked to prod
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Table 9. Average Table 8. Pigeonpea
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ance of sorghum-pigeonpea intercrop
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Mligo, J.K., 1995. Pigeonpea breedi
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To Charles Nhemachena, et al. Q: 1)
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• Assessment of the potential ben
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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