Nitrogen contributions of legume roots to cabbage nutrition

Abstract

The effects of roots are generally not considered in studies assessing crop responses to green manure. However, measuring such effects can contribute to a better understanding of crop rotation. In two experiments, we evaluated the content of legume-N in crop tissue and the fertilizer value of the roots and shoots of two legume species. Roots, shoots, or whole plants of the legumes sunhemp (Crotalaria juncea) and jack beans (Canavalia ensiformis) were cropped as green manure to supply nitrogen to cabbage crops (Brassica oleracea var. capitata). The principle of the A-value technique was applied to estimate the fertilizer value of each plant part. In a pot experiment, both the content of legume-N in cabbage and the fertilizer value of the whole plant was higher than the shoots, which was in turn higher than that of the roots. In fi eld condition, roots had a decreasing effect on the N content of cabbage plants. Growing cabbage on legume root residue resulted in an increased absorption of 15 N-urea, resulting in negative values for legume-N content:-13.59 g kg-1 and-3.51 g kg-1 for sunhemp and jack beans, respectively. Suggesting both low N supply by roots and N immobilization in soil organic matter or microbial biomass. Future research should focus on estimating the net N acquisition by plants from root residues under fi eld conditions, where rooting patterns and biomass distribution differ from those in pot experiments, therefore giving a more realistic quantitative estimate.

Contribution of Cover Crops to the Productivity of Maize‐Based Conservation Agriculture Systems in Zimbabwe

“…The high yields observed in the maize grown after jack‐bean and velvet‐bean may be attributed to the ability of the cover crops to fix more N (Boddey et al, 2006). Velvet‐bean and jack‐bean have a high N‐fixing ability with residual N values as high as 60 and 56 kg N ha −1 reported from both velvet‐bean and jack‐bean, respectively, from BNF (Okito et al, 2004; Vargas et al, 2013). The N fixed by the cover crops is contained in the cover crop residues and released as the residues decompose, thus benefiting the succeeding maize crop (Aber et al, 1990).…”

Crescimento e produção de brócolis adubado com doses de mucuna-cinza em casa de vegetação

“…Maiores doses são usadas, possivelmente, porque nem todo o N contido no adubo verde ou composto orgânico pode ser mineralizado do material vegetal no período de demanda da cultura, como verificado no presente estudo. A disponibilidade do N do adubo verde para as plantas depende, além da quantidade aplicada, de outros fatores como a mineralização do N. Entretanto é importante considerar que o N residual poderá ser aproveitado em culturas subsequentes (VARGAS et al, 2013).…”