Sunnhemp and millet as green manure for tropical maize production

Adriano Perin,José Guilherme Marinho Guerra,Gilberto Bernardo De Freitas,Ricardo Henrique Silva Santos,Segundo Sacramento Urquiaga,Paulo Roberto Cecon

doi:10.1590/s0103-90162006000500006

Abstract

Commonly N release from legume residues is rapid in the tropics. Legume mixtures with grasses can result in slower nutrient release from residues, better matching the N requirements of the following crop. The objectives of this study were to evaluate the effects of the green manures sunnhemp (Crotalaria juncea) and millet (Pennisetum glaucum), alone or mixed, on the performance of a subsequent maize crop with and without the application of N-fertilizer. The experiment consisted of four randomized blocks, with split plots. The plot treatments consisted of previous cultivation of sunnhemp, millet, mixed sunnhemp+millet and weeds. The subplot treatments were 90 kg N ha-1 and absence of N-fertilizer. Substantial amounts of biological nitrogen fixation (BNF) nitrogen were present in above ground parts of sunnhemp alone (173 kg ha-1) and mixed with millet (89 kg ha-1). Decay rates showed that half of the N was released 15 and 22 days from sunnhemp and sunnhemp+millet residues, respectively. The difference was attributed to temporary immobilization due to the higher C/N ratio of sunnhemp+millet. The preceding sunnhemp+millet treatment resulted in a larger maize yield than sunnhemp alone, when no N-fertilizer was applied. This effect was not observed when N-fertilizer was added. This effect may be due to a more timely N release, compared to sunnhemp and millet alone, when available N is required for maize. Nitrogen budgets showed that 15% and 10% in maize grain N was recovered from BNF for sunnhemp alone and sunnhemp+millet respectively. The recovery of N-BNF by maize was 65% higher after sunnhemp+millet than after sunnhemp monocrop.

Highlights

Despite the low average yield (3,400 kg ha1), maize is responsible for the largest removal of N by a single crop species in Brazilian agriculture, with an annual total withdrawal of approximately 740 thousand tons of N contained in harvested grain
Intercropping legume and grass crops can result in a residue combination that could slow down N release and help to match nutrient supply with crop demand
No significant differences were observed between sunnhemp and millet monocrops or intercropped in relation to the decomposition rate (Figure 1a, Table 2)

Summary

Introduction

Despite the low average yield (3,400 kg ha1), maize is responsible for the largest removal of N by a single crop species in Brazilian agriculture, with an annual total withdrawal of approximately 740 thousand tons of N contained in harvested grain. High N immobilization or losses through leaching (Fillery, 2001) and or volatilization (Janzen & McGinn, 1991) can occur if N is released when crop N demand is smaller than the N supply (Cobo et al, 2002b; Lahti & Kuikman, 2003). This release is affected by weather conditions, soil management, crop management practices (Fillery, 2001; Palm et al, 2001; Thompson & Fillery, 2002) and residue properties. The objective of this study was to evaluate the effects of green manure intercrop of sunnhemp and millet on the subsequent grain yield and N nutrition of maize crop

Objectives

Methods

Results

Conclusion