Integrated Soil Fertility Management Based on Pigeon Pea and Cowpea Cropping Systems Influences Nitrogen Use Efficiency, Yields and Quality of Subsequent Maize on Alfisols in Central Malawi

An integrated soil fertility management (ISFM) involving food grain legumes in predominantly maize systems is becoming popular in southern Africa. A study on diversified pigeon pea and cowpea cropping systems was conducted on Alfisols in Lilongwe and Dowa districts of Central Malawi. The objective of the study was to evaluate the residual effects of legume-legume and legume-cereal intercropping systems involving pigeon pea (PP) and cowpea (CP) when integrated with inorganic nitroen (N) fertilizer on N mineralization patterns, rotational maize (MZ) N uptake, maize yield, maize grain crude protein content (grain quality), and nitrogen use efficiency (NUE) in the forfm of partial factor productivity of applied N (PFPN). The field experiment was arranged in a split plot design with the previous legume-based systems (with residues retained) as main plots and the 0, 45, 90 and 120 kg ha−1 inorganic N rates as sub-plots. Results showed significantly higher (P < 0.05) NUE in plots that were previously legume-based of 76.5 kg grain kg−1 N applied in a previously Sole CP, compared to 39.4 kg grain kg−1 N applied in a previously Sole MZ, for Lilongwe site and 78.4 kg grain kg−1 N applied in a preciously PP + CP intercrop, compared to 40.5 kg grain kg−1 N applied in a previously Sole MZ, for Dowa site. Similarly, results from treatments that were previously legume-based consistently showed significantly higher (P < 0.05) maize grain yield increases by ranges of 30–59% at 0 kg N ha−1 and 28–42% at 120 kg N ha−1fertilizer application rate at the Lilongwe site. Similar trends were observed for the Dowa site, with the highest grain yield increase of 45% under treatment that was previously PP + CP intercrops. Maize grain protein significantly (P < 0.05) increased with additions of inorganic N by ranges of 9.0–11.4% and 10.2–13.1% for Lilongwe and Dowa sites, respectively. From this study, it is noted that the novel legume-legume cropping system involving pigeon pea and cowpea is amongst technologies that improve NUE, yields and quality of the subsequent maize crop and play a great role in sustainable agricultural intensification.