Effect of soybean (Glycine max) as a breakcrop on the cane and sugar yield of sugarcane

Abstract

The high nitrogen requirement of sugarcane is problematic for small scale farmers in Zimbabwe due to the high cost and scarcity of fertilizer. Producing legume crops in rotation with sugarcane during the fallow period may alleviate the problem. The main aim of this research was to establish whether vegetable and grain soybeans used as fallow crops in sugarcane will benefit small scale farmers. Experimental design was a split-plot design with main treatments 1) vegetable soybean used as a fallow crop, 2) grain soybean used as a fallow crop and 3) fallow treatment (control) where the land was fallowed. After the fallow period sugarcane variety CP72-2086 was planted and topdressed with either 80 kg N ha⁻¹ or 120 kg N ha⁻¹ as the subplot treatments. Leaf area index (LAI), leaf nitrogen content (N content), sugarcane and sugar yield were measured. Cane planted in vegetable soybean plots and topdressed with 80 kg N ha⁻¹ produced significantly higher cane and sugar yields compared to cane grown on fallow plots that received 120 kg N ha⁻¹. Incorporating vegetable soybeans in the system can therefore save about 40 kg N ha⁻¹ while increasing cane yield resulting in a more profitable cane production cycle.