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

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to amount of biomass, quality of biomass in terms of L+P: N ratio, litter fall, and preseason inorganic N. These results were in agreement with those reported by Mafongoya et al. 1999). Based on these results we can safely conclude that the main predictors of fallow performance are quantity of biomass, quality of the biomass, preseason inorganic N and texture on the soil. The relevance of these predictors needs to be tested over a wide range of conditions and with different fallov: species. Soil Chemical Properties The major soil chemical changes that take place under tree fallows are increases in labile pools of SaM, N stocks, exchangeable cations and extractable P (Rao et al. 1998). Details of the mechanisms of soil improvement by tree fallows were reviewed by (Buresh and Tian, 1998). In theory, planted tree fallows are expected to improve soils faster than natural fallows since the land is completely covered by fast growing leguminous trees for 2 to 3 years. However the magnitude of these soil improvements depends on tree species, length of fallow, soil and climatic conditions. In this section, we will concentra te on these changes as measured from experiments in southern Africa. Biological nitrogen fixation and N cycles The contribution of leguminous trees through N2 fixation is well recognized, although not all legumes fix N2. Nitrogen fixation in the humid and subhumid zones of Africa has been reviewed by Sanginga (1995). There has been little work on quantification of N2 fixation by trees in southern Africa. This work has proved to be difficult due to constraints in the methodologies for measurins N2 fixed. A series of multi-location trials have been set to measure the amount of N2 fixed by different tree genera and provenances (Table 3) using the 15N natural abundance method. The data on percent Ndfa shows high variability among provenances of the same species for N derived from atmospheric N2 fixation. Sanginga et al. (1990) found that percent Ndfa ranged from 37 to 74% for provenances of Leucaena leucocephala. The data shown in Table 3 falls within the range reported by Sanginga et al. (1990). These preliminary data show the huge potential of trees to fix N2 and increase N inputs in N deficient soils. Our future analysis will focus on factors responsible for this variability in N2 fixation across s~tes and how to optimize N2 fixation under field conditions. Barrios et al (1997) m~asured availability of soil N following 2- and 3-year fallows a N- deficient soils in eastern Zambia. His results confirmed that tree fallows increase N availability compared to continuous cropping without fertilization. Subsequent N measurements down to 200 cm in the soil profile showed significant N inorganic accumulation at depth during the cropping phase (Figure 2). These results show that improved fallows can create a very "leaky" N cycle after fallow clearance. Most of the N is leached beyond the rooting depth of maize and this N is released from organic inputs before peak N demand by maize. Hence there will be asynchrony between N release and N demand by maize. Consequently there is need to design systems which try to minimize N losses and increase N use efficiency, and cycling. Based on those results we designed mixed fallows of coppicing species and noncoppicing species. The hypothesis is that the coppicing species will act as a permanent "safety net" for N when the noncoppicing fallows are cut due to resprout growth and deep root system in the soil. Results of gliricidia and sesbania mixed fallows have shown higher maize prcr ductivity and efficient N cycling compared to single species fallows (Figure 3). Soil acidification and cations There are several reports on soil pH and improved fallows. Topsoil pH decreased under fallows of Acacia auriculiformis (Drechsel et al. 1996). However Oonsson et al. 1996) found no changes in soil pH after fallows. Our results over a 10-year period showed significant decrease in topsoil soil pH, 0-60 cm and an increase in soil pH with depth (Figure 5). This decrease in topsoil pH and increase in soil pH is attributed to leaching of N03 and cations such as magnesium as shown in Figure 6. The movements of cations from the topsoil were also confirmed by low CEC in 0-20 cm (6.25 compared with 9.50) in the 20-100 cm soil profile. These pH changes, which will take place after fallows, may have little effect Table 3. Biological nitrogen fixation (%BNF) of coppicing species/ provenances across three sites in eastern Zambia after 1 year of growth Kalichero Kalunga Masumba Treatment %BNF Nkg/ha %BNF Nkg/ha %BNF N kg/ha A. angustisma 52.1 210.4 61.8 201.4 54.8 260.8 C. calothyrsus 48.4 81.4 44.1 214.4 48.7 193. G. sepium 79.2 212.4 71.4 408.4 70.8 297.5 l. collinsii 74.7 303.2 57.2 236.7 102.1 475.9 l. diversif(Jlia 35/88 77.5 196.8 33.8 88.6 50.0 161.1 l. diversifolia 53/88 58.4 121.5 14.0 40.5 46.9 112.6 l. esculenta 52/87 70.9 99.3 . 46.6 110.1 46.7 274.5 l. esculenta·Machakos 84.7 223.6 35.2 120.2 69.0 538.0 l. pallida 58.6 87.8 33.7 125.2 44.7 168.1 146 Grain legumes and Green Manures for Soil Fertility in Southern Africa
pH -0.40 -0.20 0.00 0.20 0.40 0.60 0.80 1.00 20 40 60 K80 ;; 100 c ~ 120 140 160 180 200 __ dena feb02-Noll97 -e-dena Noll9B-NoII97 Figure 5. Changes in soil pH as affected by two-year fallow species and soil depth at Msekera, eastern Zambia on maize productivity in base rich soils. However their long term effects on acidic, low-activity clay soils may have a major effect on crop yields and threaten the long-term sustainability of improved fallows. Management practices such as zero tillage after fallows and regular application of lime may have to be adopted to deal with such problems of decrease in pH and cation leaching. Soil carbon and improved fallows The debate on carbon and global warning has gained momentum. Of late, there has been increased scientific interest in measuring carbon sequestration in different land use systems to mitigate climate change issues. Agroforestry land use systems have been cited to sequester the most soil C without a lot of scientific evidence. We monitored soil C in long-term trials with improved fallows. There were significant increases in soil carbon in the topsoil as compared to deep horizons (Table 4). These results are in agreement with those of Onim et al.; (1990) in western Kenya using improved fallows. Of scientific and practical importance is how is the carbon protected against loss after fallow clearance. Our research program is looking how different soil aggregates store C and how soil aggregation is affected by soil texture and fallow management over the long term. This will enable us to model carbon dynamics and climate change. Table 4. Amount of organic carbon (%) measured in different soil depths under a two·year non·coppicing fallow species at Msekera, eastern Zambia Year Soil depth (em) 1997 2002 Percent increase 0·20 0.95 1.i 2 17.89 20-40 0.78 0.94 20.51 40·S0 O.Sl 0.77 2S.23 SO·100 0.51 0.55 7.84 100·150 0.3S 0.49 3S.11 150·200 0.28 0.37 32.14 SED 0.05 O.OS 20.00 c mol kg" 0.3 0.5 0.7 0.9 1.1 1.3 1.5 o+---~--~--~--~--~~~ 20 40 E 60 .!!. 80 '-e-Cc ị. 100 -+-M+f ~ 120 -->
Page 2 and 3:
Grain Legumes and Green Manures for
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Acknowledgments • The Leopard Roc
Page 6 and 7:
Evall!ating mucuna green manure tec
Page 9:
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
Page 20 and 21:
Dvorak KA 1996. Adoption potential
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LEGUMES FOR SOIL FERTILITY IN SOUTH
Page 25 and 26:
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
Page 91 and 92:
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
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
Page 116 and 117: Table 3. Above·ground biomass (t/h
Page 118 and 119: and horticulture in Zimbabwe: Case
Page 121 and 122: GRAIN LEGUMES AND GREEN MANURES IN
Page 123 and 124: Results Table 1. Adaptation of gree
Page 125 and 126: Four rates of fertilizer N were app
Page 127 and 128: THE ROLE OF COWPEA (VIGNA UNGUICULA
Page 129 and 130: Table 1. Non-legume cropping patter
Page 131 and 132: Table 9. Common pests on cowpeas as
Page 133 and 134: few of the farmers interviewed acqu
Page 135: Murwira, H.K., M.J. Swift and P.G.H
Page 138 and 139: Materials and Methods On farm exper
Page 140 and 141: 18000 1600) 14000 a) Zambia 12000 m
Page 143 and 144: EFFECT OF DIFFERENT GREEN MANURE LE
Page 145 and 146: .. ~ Table 2. The effect of time o
Page 147: Chivinge, O.A., E. Kasembe, and I.K
Page 150 and 151: times with regionally specific adap
Page 152 and 153: ter content at 180 cm was still wel
Page 156 and 157: with the natural fallow, which did
Page 158 and 159: and K to maize as an equivalent amo
Page 160 and 161: forts to understand the mechanisms
Page 162 and 163: gen recovery rates in relation to p
Page 164 and 165: The first steps to improve soil fer
Page 167 and 168: Questions and Answers .Identificat
Page 169 and 170: MUCUNA - MAIZE ROTATIONS AND SHORT
Page 171: Table 3. Percent nitrogen (% N) con
Page 174 and 175: ~e decomposition of legume residues
Page 176 and 177: Table 3. Effect of forage legumes o
Page 178 and 179: available nutrients and vice versa,
Page 180 and 181: Conclusion and Recommendation Mucun
Page 182 and 183: Specific objectives were to: • Te
Page 184 and 185: '"~ v '" ~ ~ 1400000 1200000 100000
Page 187 and 188: EFFECT OF SURFACE APPLICATION AND I
Page 189: it 4 a···· · ... - :.!! e.....
Page 193 and 194: PERFORMANCE OF GREEN MANURES AND GR
Page 195: 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
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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
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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
Page 228 and 229:
Results and Planning Workshop. Soil
Page 231 and 232:
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
Page 239 and 240:
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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