Yield gaps, nutrient use efficiencies and response to fertilisers by maize across heterogeneous smallholder farms of western Kenya

The need to promote fertiliser use by African smallholder farmers to counteract the current decline in per capita food production is widely recognised. But soil heterogeneity results in variable responses of crops to fertilisers within single farms. We used existing databases on maize production under farmer (F-M) and researcher management (R-M) to analyse the effect of soil heterogeneity on the different components of nutrient use efficiency by maize growing on smallholder farms in western Kenya: nutrient availability, capture and conversion efficiencies and crop biomass partitioning. Subsequently, we used the simple model QUEFTS to calculate nutrient recovery efficiencies from the R-M plots and to calculate attainable yields with and without fertilisers based on measured soil properties across heterogeneous farms. The yield gap of maize between F-M and R-M varied from 0.5 to 3 t grain ha-1 season-1 across field types and localities. Poor fields under R-M yielded better than F-M, even without fertilisers. Such differences, of up to 1.1 t ha-1 greater yields under R-M conditions are attributable to improved agronomic management and germplasm. The relative response of maize to N-P-K fertilisers tended to decrease with increasing soil quality (soil C and extractable P), from a maximum of 4.4-fold to -0.5- fold relative to the control. Soil heterogeneity affected resource use efficiencies mainly through effects on the efficiency of resource capture. Apparent recovery efficiencies varied between 0 and 70% for N, 0 and 15% for P, and 0 to 52% for K. Resource conversion efficiencies were less variable across fields and localities, with average values of 97 kg DM kg-1 N, 558 kg DM kg-1 P and 111 kg DM kg-1 K taken up. Using measured soil chemical properties QUEFTS over-estimated observed yields under F-M, indicating that variable crop performance within and across farms cannot be ascribed solely to soil nutrient availability. For the R-M plots QUEFTS predicted positive crop responses to application of 30 kg P ha-1 and 30 kg P ha-1 + 90 kg N ha-1 for a wide range of soil qualities, indicating that there is room to improve current crop productivity through fertiliser use. To ensure their efficient use in sub-Saharan Africa mineral fertilisers should be: (1) targeted to specific niches of soil fertility within heterogeneous farms; and (2) go hand-in-hand with the implementation of agronomic measures to improve their capture and utilisation

Yield trends in the long-term crop rotation with organic and inorganic fertilisers on Alisols in Mata (Rwanda)

A crop rotation system with various species was established on Alisols at Mata grassland site, oriental side of Zaire-Nile Watershed Divide (CZN), Rwanda. Inorganic and organic fertilizers were applied in various plots under randomized complete blocs with three replicates. Crop yield data for each season were recorded over a 9-year period. Results showed that there was very low or no harvest in plots without fertilizers. In plots with fertilizers, the yield generally increased but remained relatively low, few crops and varieties adapted to the Mata ecology, only potatoes [Solanum tuberosum] and finger millet [Eleusine coracana] responded well to fertilizers. Liming was absolutely necessary to get any acceptable crop yield improvement with NPK. High rate of rich farmyard manure was efficient and its effect was recorded up to 4 seasons after four regular seasonal applications. Mata compost (C:N >25, 0.3 g P kg-1) had little beneficial effect. One, four and half, and eight tonnes of lime per ha applied 3 times in 8 years increased soil pH (in water) but not up to 6.5. It is concluded that to improve food production at the CZN area, selection of crops and varieties to fit ecological conditions and amending soils to fit crops must be considered

Six month-duration Tephrosia vogelii Hook. f. and Tithonia diversifolia (Hemsl.) A. Gray planted-fallows for improving maize production in Kenya

An experiment including planted Tephrosia vogelii and Tithonia diversifolia fallow species and natural fallow was conducted at Maseno, Kenya, for assessing whether these fallows grown on a nutrient depleted land could produce sufficient green manure in six month period, whether their biomass retained on the same plots or transferred to continuously cropped plots with or without added P fertiliser could increase yield of consecutive maize crops and whether it is useful to regularly repeat these fallows on same plots. First fallow was established in randomized complete blocks with three replicates. At harvesting, biomass was recorded, then either incorporated in situ or transferred to continuous cropped plots split with and without added P fertiliser and monitored for the effect in improving consecutive maize crops. The second fallow was managed on this split plot design. The two-planted shrubs fallows produced more than 9 Mg total dry biomass and accumulated 154 to 234 kg N.ha-1, which were significantly higher compared to the production in the natural fallow. The shrubs were also superior to natural fallow for P accumulation (5-22 kg versus 2 kg.ha-1). The aboveground dry biomass harvested from planted T. vogelii and T. diversifolia and either incorporated in situ or transferred into continuously cropped plots increased maize yields by 2.5 folds compared to the unmanured crop, the control. Supplementing the organic materials with an additional 20 kg P inorganic fertilizer increased the 1st maize yield by about 40%. Productivity in the plots with T. vogelii or T. diversifolia aboveground biomass removal was low for the subsequent fallow and maize crops when compared to the performance in plots where biomass was incorporated. To achieve sustained yields of maize in depleted soils requires regular improved fallowing at least one season alternating with one season maize, and additional P inputs

Soil use and management strategy for raising food and cash output in Rwanda

Rwanda is a poor country and land is scarce, with only 0.65 ha of suitable farmland per household. Literature search for identifying constraints and solutions to productive and sustainable agriculture and livestock production was carried out. The country is facing with increasing soil fertility depletion and erosion due to steep landscape, continuous cultivation and high but not well distributed rainfall. Crops adequately allocated to the 0.65 ha farmland may produce enough food for energy and protein, but not cooking oil; animal production for meeting fat requirements is already at the limit. Forest resources are insufficient to produce necessary poles, timber, fuel and other forest-related products; alternatives must be found. Strategies to raise agricultural production include soil and water conservation, fertility improvement, irrigation and drainage, high-yielding plant varieties, improved animal management, pest control and reduction of postharvest losses. Labour shortage at critical periods of agricultural operations can be reduced through appropriate mechanisation. Such improvements that are high demanding in investments may substantially raise crop and livestock production, allowing Rwanda to develop agro-industries and the commercial sector. Alternatively but carefully, preference may be given to investments in high-value exports that can pay for imports of food, fuel and other necessities

Fertilisation continue des Oxisols acides non humifères du

Crop rotation system of maize and beans, established at Rubona (Rwanda) from 1984 to 1992, was used to evaluate different types and rates of fertilizers in improving the productivity of acid Oxisols. Continuous cropping of maize followed by beans for a period of 8 years gave no yield in control plots. Asingle application of 2 t per ha of lime increased significantly (p = .01) the soil pH, Ca2+ content, cationic exchange capacity, and decreased the level of the exchangeable aluminium. This quantity of lime when applied every two years for a period of eight years led to overliming. The application of more than 8 t per ha of fresh farmyard manure (annually), combined to 300 kg per ha of NPK 17:17:17 (every six months) significantly improved soil organic C and crop production at Rubona. The high rate (35 t per ha) of fresh manure or the combination of “lime, manure and NPK fertilizers” gave the best crop performance. Ten tons of farmyard manure (dry matter) per ha and per year seems to be the minimum acceptable amount which can effectively substitute for inorganic fertilizers