Integration of Grain Legumes and Mbeya Manure Improves Maize Productivity on Smallholder Farms in Central Malawi

Legumes are integrated in maize-based systems to improve soil fertility and crop productivity. However, the ecosystem services from legumes vary. Crop rotation on-farm studies were conducted over two cropping seasons (2018/19 and 2019/20) in Mkanakhoti and Kaluluma Extension Planning Areas (EPAs) in Kasungu district, central Malawi. The main objective of this study was to evaluate maize response to legume cropping systems and mbeya manure. In the first season (2018/19), five treatments including sole groundnut (Gn), sole soybean (soy), sole pigeon pea (PP), and doubled-up legumes (legume + legume intercrop) - pigeon pea intercropped with groundnut (Gn+PP), and pigeon pea intercropped with soybean (Soy+PP) were grown. In the second season (2019/20), maize was planted on plots that had either sole or doubled-up legumes. These plots were split into two, one half was top dressed with 23kg N ha-1 only and the other half received 23kg N ha-1+1000kg ha-1 mbeya manure. The experiments were replicated in 2019/2020 and 2020/2021 seasons. Soil fertility was low and highly variable between farms in the study sites. Soil pH, total nitrogen (N), available phosphorus (P), organic matter (SOM) and active carbon in topsoil (0-15cm) averaged 5.1±0.5, 0.19±0.18%, 31±19.6 ppm, 1.4±0.34 %, and 193±74 mg kg-1, respectively. Application of mbeya manure to maize increased leaf chlorophyll and plant height (p<0.05). There were variations in maize yield responses to legumes with higher benefits obtained from maize rotated with doubled-up legumes than sole legumes. The results also showed that on non-responsive soils, overall, the use of mbeya manure in combination with legume systems increased the rotational maize grain yield by 88% over maize following legumes only (p<0.05), with highest yields from doubled up legumes/maize rotations followed by groundnut/maize rotations. It is therefore recommended that on highly degraded soils, farmers can increase maize productivity through integrated soil fertility management involving a combination of 23kg N/ha and 1000kg/ha of mbeya manure applied to maize rotated with doubled-up legumes (Gn+PP or Soy+PP) and sole groundnut (Gn). Key words: Doubled-up legumes, crop rotation, groundnut, pigeon pea, soybean, maize, mbeya manure