Abstract:
Nitrogen (N) is the critical plant nutrient. Low maize (Zea mays L.) yields in smallholder farms of Malawi are attributable to declining N fertility, aggravated by the ever increasing price of fertilizer. Maize, the country’s staple, has a high nitrogen demand. Little effort has been made to establish the best nitrogen rate in a maize- cowpea and maize-bean intercrop under variable soil conditions as a way of improving production, and was the objective of the current study. Field experiments were conducted at Chitedze Agricultural Research Station in Lilongwe and Makoka Agricultural Research Station in Zomba during the 2016/17 growing season. A split plot layout in a randomized complete block design, with three replicates was used. The main plots were; sole maize, sole bean, sole cowpea, bean/maize and cowpea/maize intercrop systems. The sub plots were N fertilizer rates (0, 52.5, 78.75 and 105 kg N ha-1), applied as urea. Measured parameters included plant height, leaf area index, and N uptake by the maize plant, dry matter and grain yield, legume biomass and yield, land equivalent ratio, weight and number of nodules and nutrient use efficiency. The data was subjected to analysis of variance using SAS software version 9.3 (SAS Institute Inc.) at P<0.05. Means were separated using Duncan Multiple Range (DMRT) test at 95% significance level. The results showed that application of N fertilizer and legume integration increased maize grain yield and that 105 kg N ha-1 was optimal mineral N fertilizer rate for maximum maize grain yield per unit area. Maximum maize Nitrogen use efficiency (NUE) (48.63 kg/kg) was obtained at application rate of 78.75 kg N ha-1 and the minimum value (44.86 kg/kg) was recorded at the highest N rate (105 kg N ha-1). Application of mineral N fertilizer increased N uptake by maize while legume intercrops did not have any significant (P˂0.05) effect on uptake. Maize grain and dry matter yield were significantly (P˂0.05) affected by the application of mineral N fertilizer but not by legume intercrops. The effect of cropping system × N level interaction was significant (P˂0.05) on N uptake by maize, maize DM (Dry matter) yield but not on maize grain yield, higher values were obtained under bean/maize intercropping x 105 kg N ha-1. Maize planted at Chitedze had significantly taller maize plants, higher maize grain yield, cob weight and 100 maize seed weight than Makoka. The land equivalent ratio (LER) values obtained for intercropping were higher than one and confirm the advantage of intercropping over sole cropping system.
