Effets de deux incorporations d'engrais verts sur le rendement et la nutrition en azote du blé (Triticum aestivum L.), ainsi que sur les propriétés physiques et biologiques du sol

Abstract

The effects of two applications of green manures (1993 and 1995) on soil physical and biological properties, on wheat (Triticum aestivum L.) yields and N uptake were investigated in 1996 in a Le Bras loam (Humic Gleysol). The green manures as main factor were clover (Trifolium pratense L.), buckwheat (Fagapyrum esculentum L.), millet (Sorghum sudanensis L.), mustard (Brassica hirta Moench), colza (Brassica campestris L.) and a control without green manure. The sub-factors consisted of four N fertilizer rates for subsequent wheat: 0, 30, 60 and 90 kg N ha−1. Green manure application significantly increased the soil water stable aggregates (MWD), and the > 0,25 mm fractions of water-stable aggregates (P < 0,05). Levels of soil microbial biomass, alcaline phosphatase and urease activities, and the N mineralization potential were also significantly increased by green manure treatments compared to the control. A 200 to 300% increase in wheat yields and N uptake were obtained, depending on green manure species, compared to the control. The results of this study provide quantitative evidence that wheat yields and N uptake increases were mainly due to N addition into soil and the improvement in soil physical and biological properties by green manure application. Key words: Green manure, wheat yields and N uptake, water stable aggregates, microbial biomass, N mineralization potential, soil enzymes