Legumes in soil fertility management: The case of pigeonpea in smallholder farming systems of Zimbabwe

We investigated the current use of legumes in soil fertility management and the feasibility of promoting use of pigeonpea in smallholder farming systems of a Communal Area in Northeast of Zimbabwe. Participatory rural appraisal methods were used to establish farmer management strategies and perceptions on major constraints to crop productivity. Soil fertility parameters were evaluated through farmer participatory experiments. The study revealed limited cultivation of legumes for both human nutrition and soil fertility management. Legumes were generally regarded as women's crops, and therefore minor, because of men's domination over women in the household decision-making process. Balancing gender interests in terms of allocation of inputs and distribution of benefits at household level was identified as a major challenge to the implementation of legume technologies. Poor extension thrusts with respect to legume production, and poor agronomic practices were identified as major production constraints. Over-emphasis on maize in the current extension packages led to the relegation of legumes to the status of 'minor crops'. Participatory experiments suggested that pigeonpea can be successfully grown by farmers under poor soil fertility conditions. The crop yielded about 3 to 9 t ha-1 of shoot biomass in a single cropping season, and up to 23 t ha-1 after two seasons of growth. High amounts leaf litter released by the crop in one season (up to 3 t ha-1) are considered a potentially viable source of nutrients for subsequent crops, as confirmed by a 22% maize yield increase obtained from a field that was previous cultivated with pigeonpea. RÉSUMÉ Les investigations sur l' utilisation des légumineuses dans la gestion de fertilité du sol ainsi que les possibilités d' incorporer le pois cajan dans le système agricole de petits fermiers ont été fait dans un milieu rural au Nord-Est du Zimbabwe. La méthode "Participatory rural appraisal" a été utilisée pour déterminer les stratégies de gestion du sol et les perceptions qui contribuent à la réduction de la productivité de la récolte. Les paramètres de fertilité du sol ont été analysés en collaboration avec des agriculteurs. Cette étude a révelé qu' il y a une utilisation limitée de légumineuses dans l' alimentation des gens ainsi que dans la gestion de fertilité du sol. Les légumineuses sont géneralement considérées commes la récolte pour les femmes, sur ce, de peu d' importance, et à cause de la domination des hommes dans la prise de décision dans le foyer. L'exécution des téchnologies d' incorporer les légumineuses dans le système de production agricole s' est heurtée à un problème majeur de domination de l'homme, ses préférences dans la répartition et la distributions des intrants et les bénéfices. Un autre problème identifié, c'est une vulgarisation très limitée de la production de légumineuses et une difficile adaptation agronomique de variétés de légumineuses qui sont déjà dans le système. Le système de vulgarisation existant s'est concentré plus sur la production du maïs, ce qui a mené à considérer les lègumineuses commes les plantes de moins d' importance. Les expériences participatives ont suggeré que le pois cajan peut être produit par les fermiers dans des sols moins fertiles. La production a été estimée de 3 à 9 t ha-1 de biomasse dans une seule saison de production, et de 23 t ha-1 après deux saisons. Une quantité considérable de litière de feuilles venant de plantes dans une seule saison (jusqu'a 3 t ha-1) est considéree comme une source importante de nutriments pour les plantes consécutives, comme l' augmention de 22% de production de maïs l'a confirmé après une culture de pois cajan. (Af Crop Science and Production: 2001 9(4): 629-644

Physiological diversity of rhizobia nodulating promiscuous soyabean in Zimbabwean soils

Rhizobial isolates were obtained from nodules of promiscuous soyabean varieties Hernon 147 and Magoye and specific Roan grown in a range of Zimbabwean soils. A total of 129 isolates authenticated as true rhizobia were characterized using growth rate, elasticity, colour, size, colony shape, acid/alkali production on YEM and tolerance to low and high pH, elevated temperature and salt concentration. Isolates separated into 2 major clusters at a similarity level (%SSM) of 66%. Cluster I contained isolates forming dry colonies (77%) which separated into 9 groups and Cluster II contained those forming the wet colonies (23%) with 4 groups. Acid and salt tolerance patterns did not differ among the two main clusters (the dry and the wet colony types). More isolates forming wet colonies (47%) survived at 40°C than those forming dry colonies (13%). Salt, temperature and acid pH tolerance were not related to geographic origin of the isolates. The promiscuous soyabean variety Magoye nodulated with the widest range of rhizobia (12 groups) followed by Hernon 147 (11 groups) and then Roan (9 groups). Guruve soils had the most diverse range of isolates belonging to 12 groups followed by those from Chiweshe (9 groups) and then those from Chikomba (8 groups). Our results indicate that soyabean is nodulated by a wide range of indigenous rhizobia in African soils

Manure and soil properties affect survival and persistence of soyabean nodulating rhizobia in smallholder soils of Zimbabwe

Persistence of the soyabean rhizobial inoculant strain MAR 1491 was assessed in 52 soils from Guruve, Hurungwe and Goromonzi districts of Zimbabwe, which had been inoculated 1¿4 or 6 years previously. Most probable number estimates of rhizobia in the soils showed that population sizes decreased with increasing time since the last inoculation. Rhizobial populations of up to 102 cells g¿1 soil were found in Guruve soils inoculated 3 years before, while persistence in Hurungwe and Goromonzi soils was significant for soils inoculated 2 years before. The greater rhizobial persistence in Guruve soils was attributed to their higher clay (>20%) and organic C (>1%) compared with the sandier, relatively less fertile Hurungwe and Goromonzi soils. Farmers with favourable soils such as those in Guruve can grow soyabean for at least 3 years without the need for repeat inoculation. Manure application led to increased indigenous rhizobial numbers at two smallholder sites and larger numbers of rhizobia in inoculated plots in sandy soils from Goromonzi. Inoculation and manure addition increased rhizobial numbers and soyabean yields in field experiments; soyabean yields varied from 0.5 t ha¿1 in uninoculated, unmanured plots to 1.1 t ha¿1 in inoculated plots receiving 10 t manure ha¿1. Increases in numbers closely followed the progress of the wet season. The highest rhizobial population of 105 cells g¿1 soil was obtained in plots that had received 10 t ha¿1 manure when a high soil moisture (15%, w/w) was recorded during the cropping season, while the lowest population of 101 cells g¿1 soil was recorded in treatments during the dry season when soil moisture was low

Symbiotic effectiveness and host ranges of indigenous rhizobia nodulating promiscuous soyabean varieties in Zimbabwean soils

Presence of indigenous rhizobia nodulating promiscuous soyabean was determined in 92, mainly sandy soils, from wetter agro-ecological zones of Zimbabwe suited to soyabean production. A total of 129 isolates were obtained from nodules of promiscuous soyabean varieties, Magoye and Hernon 147, and a specific variety, Roan grown in potted soils. Magoye nodulated in 80%, Hernon 147 in 50% and Roan in only 25% of the 92 soils tested. Rhizobia populations ranged from undetectable to 2.4×104 cells g-1 of soil. Twenty-one of these isolates were tested for symbiotic effectiveness on two varieties, promiscuous Magoye and specific Roan. Differences in parameters such as nodule numbers, nodule weights and total N fixed reflected diversity among the indigenous isolates. Three isolates had significantly higher N2-fixing potential in comparison with the commercial strain MAR 1491 on promiscuous Magoye. Host ranges of 34 isolates were evaluated on nine legume species: Arachis hypogaea, Cajanus cajan, Crotalaria juncea, Glycine max, Macroptilium atropurpureum, Phaseolus vulgaris, Sesbania sesbania, Vigna subterranea, Vigna unguiculata. Of these 34 isolates, 33 formed nodules with M. atropurpureum of which 61% were moderately effective to very effective while all nodulated V. unguiculata with 58% being moderately effective to very effective. Twenty-eight isolates nodulated V. subterranea and C. cajan (short season variety) with 76 and 36% of these being moderately to very effective, respectively. None of the isolates formed nodules on Phaseolus vulgaris, Arachis hypogaea or Sesbania sesban. Our results indicate that the ability of even specific varieties of soyabean to nodulate with indigenous isolates in African soils is greater than generally assumed

Opportunities for the introduction of pigeon peas into smallholder farming systems in Zimbabwe.

Smallholder agriculture in Zimbabwe is characterised by maize monoculture. Several other crops, especially legumes, have received little attention despite their agronomic potential and nutritional value. The pigeon pea is a well-known multipurpose crop in subsistence agriculture, yet none of its useful attributes have been exploited in Zimbabwe. In this study, the feasibility of intervening with pigeon peas in smallholder farming systems was investigated in Mukarakate area of Murehwa Communal Lands and revealed a limited use of legumes in both human nutrition and soil fertility management. The lack of a well co-ordinated agenda to promote legume production, and a poor agronomic performance by the currently grown legumes because of the low fertility and pH of the soils were identified as some of the main constraints. Limitations imposed by the biophysical and economic environments in agricultural production at local level were also identified. The potential place of pigeon peas as perceived by farmers is discussed in the context of on-going pigeon pea experiments designed to investigate the potential contribution of this crop to soil fertility. Transactions of the Zimbabwe Scientific Association Volume 72 (Supplement) 1998, pp. 60-6

Vesicular arbuscular mycorrhizal fungi prevalence and diversity in Zimbabwean soils

The prevalence and population levels of VAM fungi in a range of field soil environments in Zimbabwe were determined. The main VAM genera Acaulospora, Scutellospora, Gigaspora, Glomus, Sclerocystis and Entrophospora were represented in the study sites. The relative abundance was Glomus>Scutellospora>Sclerocytis>Gigaspora>Entrophospora at all sites except at Chabwino (fallow soil) and Thorn Park (sorghum) where Acaulospora>Scutellospora and Sclerocytis>Scutellospora = Acaulospora. Relative proportions of different VAM genera were similar across soils but population sizes varied with soil management. There was no clear relationship between VAM spore numbers and cropping history although among the cultivated plots, soils that had legumes as the previous or current crop generally had higher VAM populations than under sorghum. Of the soil parameters measured, only percent organic carbon was significantly correlated with VAM numbers and infective propagules. Journal of Applied Science in Southern Africa Vol.5, No.1 pp. 35-4

Tapping indigenous herbaceous legumes for soil fertility management by resource-poor farmers in Zimbabwe

A 2-year study was conducted in three rainfall zones of Zimbabwe to explore opportunities for harnessing biological nitrogen fixation of non-cultivated herbaceous legumes, which hitherto have been regarded simply as weeds, in order to improve soil productivity on smallholder farms. The rainfall zones used ranged from sub-humid (800 mm annually) to semi-arid (50 kg N ha-1. While such relatively small amounts of N input may not result in dramatic yield increases for subsequent crops, they may make a critical contribution towards reversing the highly negative nutrient balances prevailing on the fields of resource-poor farmers. Overall plant biomass yields wer