Elsevier

Field Crops Research

Volume 68, Issue 1, 29 September 2000, Pages 75-83
Field Crops Research

Annual soil improving legumes: agronomic effectiveness, nutrient uptake, nitrogen fixation and water use

https://doi.org/10.1016/S0378-4290(00)00113-1Get rights and content

Abstract

Annual soil improving legumes have a role in the management of soil fertility under the low-input management conditions of resource poor farmers. Several species have been identified as promising for the sub-humid tropical areas of eastern Africa having bi-modal rainfall. Most of these can be intercropped with species used for food and/or have alternative uses for food, forage or weed suppression. We compared five annual legumes for fixation of atmospheric nitrogen, soil water uptake, soil P and nitrate recovery, effects on subsequent crops and for phosphorus recovery from Busumbu P rock. Canavalia [Canavalia ensiformis (L.) DC] produced the most biomass, fixed the most N, was most efficient in extraction of soil nitrate, and supplied the most N to subsequent food crops. Not unexpectedly, it was also most effective in improving soil productivity. Mucuna [Mucuna pruriens (L.) DC var. utilis] produced less biomass than canavalia but derived a greater proportion of plant N from the atmosphere, while crotalaria [Crotalaria ochroleuca G. Don.] and lablab [Lablab purpureus (L.) cv. Rongai] fixed little nitrogen. Lablab and soybean [Glycine max (L.)] produced the least biomass. All legumes and food crops failed to acquire significant amounts of P from Busumbu soft rock on this moderately acidic soil. The ratios of C:P in the legume biomass were high enough to cause an early net immobilization of P. Profile soil water status was highest under soybean and lowest under canavalia, reflecting differences in biomass production by the legumes and the subsequent maize–bean intercrop. Surface soil water was similar for all species, but differences were evident at depth. All legumes except soybean extracted water below 1.3-m depth.

Introduction

Legumes can play a role in the maintenance of soil productivity in low-input farming systems through N2 fixation, recovery of deep nutrients and addition of organic material to the soil. Used to improve short-term fallows, they offer additional potential benefits as forage and as components of conservation tillage systems.

In conservation tillage, legumes may contribute to weed suppression (Manyong et al., 1996), reduce labor required for the following crop (Fischler and Wortmann, 1999), and provide soil cover to reduce soil and water loss. By allowing the legumes to mature, more biomass with moderately high carbon:nutrient ratios is produced and more nutrients are accumulated as compared to legumes cut and incorporated into the soil while still immature (Fischler et al., 1999). The benefits to subsequent crops persist longer. Resistance to soil surface penetration was also less with surface application of mature legume plant material. Surface application of plant materials of lower quality (Heal et al., 1997) can improve the synchrony of nutrient supply with crop demand (Myers et al., 1994) as compared to incorporation of high quality materials with rapid nutrient release. Nutrient mineralization rate is reduced with surface application but physical factors, such as repeated wetting and drying, contribute to decomposition (Duxbury et al., 1989; Luna-Orea et al., 1996).

Giller and Wilson (1991) reported estimates of N2 fixation ranging from 23 to 250 kg N ha−1 with a median of 110 kg N ha−1 for annual legumes with growth periods of 100–150 days. Grain legumes also obtain N from the atmosphere, but may have negative N balances due to significant N removal in the grain (Karlen et al., 1994).

Cropping systems benefit from the accumulation of N if a major proportion is derived from the atmosphere or from deep in the soil profile. Root distribution patterns vary with species with canavalia [Canavalia ensiformis (L.) DC] observed to have a deeper root system than several other annual legumes (Purseglove, 1968; Fischler, 1997).

Improved fallows are not likely to greatly improve the P status of soils as available P in the sub-soil is likely to be little (Buresh and Tian, 1998) and the legumes primarily use crop available phosphorus. On P deficient soils, P must be supplied from other sources to enable a crop to efficiently use N supplied by the fallow (Jama et al., 1998).

In Uganda, the Busumbu rock phosphate deposits include soft rock composed of fine earth material (5–7% P), and hard rock ore (13% P) (Davies, 1956; Van Kauwenbergh, 1991). Unprocessed Busumbu soft P rock was not reactive in a maize–bean rotation over four seasons, but may be more reactive in the rhizosphere of vigorously growing legumes, where soil pH may be reduced due to N fixation. Negatively charged organic compounds, such as citrates and oxalates, produced by hydrolysis of organic material, may chelate Ca2+ ions and thus lower Ca2+ ions in the soil solution providing a driving force for the dissolution of P rock (Hammond et al., 1986).

Water use by legumes may vary due to differences in canopy cover and rooting habits. In rotations, deep-rooted crops may use water at depth thus obviating access by the subsequent crop (Gachene et al., 1997), whereas legumes with a lower water requirement may conserve soil water (Roder et al., 1989). If legumes extend ground cover either temporally (off-season cover) or spatially (greater canopy cover), infiltration may improve with less subsequent runoff.

The farming systems of central and eastern Uganda are typified by agronomic and biological diversity with farms of 1 or 2 ha, with several legumes already identified as promising (Wortmann et al., 1994; Fischler et al., 1999; Fischler and Wortmann, 1999).

The objectives of this research were to evaluate several annual legume species for fixation of atmospheric N2, and recovery of soil water, soil P and nitrate. Legume effects on the performance of subsequent maize–bean [Zea mays L. and Phaseolus vulgaris L.] intercrop and on P availability from Busumbu rock P were also evaluated.

Section snippets

Experimental site

Field experiments were conducted at Senge Farm (0°25′N, 32°31′E, 1200 m asl) near Kawanda Agricultural Research Institute. The site has a bi-modal rainfall distribution of about 1220 mm per year with wet seasons occurring from March to June with a peak in April, and from August to December with a peak in November. Composite samples of the deep, well-drained, red, sandy clay loam (Rhodic Kandhapludalf) soil taken to 0.2 m depth had a pH of 4.9 and organic C concentration of 25 g kg−1 (Foster, 1971).

Legume growth and P acquisition

Canavalia produced more plant biomass in both seasons (9.84 Mg ha−1, mean of two seasons) than the other legumes and soybean produced the least (1.55 Mg ha−1) (Table 2). Legume growth was not significantly affected by P application in 1997, but the increased growth due to application of TSP, as compared to the rock P treatments, was significant in 1998 and with the analysis combined across years.

There was a significant species by season interaction for P concentration in the plant tissue possibly

Conclusions

In this study, canavalia was most effective in improving soil productivity as indicated by the performance of subsequent maize and bean crops. This was probably due to high levels of N fixation, nitrate extraction and biomass production. It extracted water at 1.7-m depth, and presumably acquired nutrients to this depth. Mucuna fixed much N, but was less effective in improving productivity than some legumes that derived less N from the atmosphere; the reasons are not clear. Soybean was

Acknowledgements

The authors are grateful to: NARO and the Director of Research for Kawanda ARI for providing land, facilities and other assistance for this research; Ms. G. Nakulenge and J. Katongole for providing technical assistance; Dr. P. Smithson of ICRAF for assistance with analyses of samples; and the Canadian International Development Agency, Rockefeller Foundation, and Swiss Development Cooperation for funds provided.

References (27)

  • H.L Foster

    Rapid routine soil and plant analysis without automatic equipment. I. Routine soil analysis

    E. Afr. Agric. For. J.

    (1971)
  • Gachene, C.K.K., Makau, M., Haru, R., 1997. Soil moisture extraction of different legume crops. In: Proceedings of the...
  • Giller, K.E., Wilson, K.J., 1991. Nitrogen Fixation in Tropical Cropping Systems. CAB International, Oxon, UK, p....
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