IMPROVED SOIL QUALITY AND BARLEY YIELDS WITH FABA-BEANS, MANURE, FORAGES AND CROP-ROTATION ON A GRAY LUVISOL

There exists a need (i) to test, whether equal or better cereal yields could be obtained using cropping systems which rely on renewable reso urces rather than on fertilizer nitrogen; and (ii) to discover the con dition of the soil resource under these systems. The long-term croppin g systems on a Gray Luvisol at Breton were studied. They included: (i) an agro-ecological 8-yr rotation (AER), established in 1981, which in volved addition of both fababean green manure and manure from livestoc k fed with forages and fababeans grown in the rotation: (ii) a continu ous grain (barley) system (CG), with fertilizer N at 90 kg ha-1 y-1, e stablished in 1981; (iii) a classical Breton 5-yr rotation (CBR) invol ving forages and cereals, with no return of crop residues or manure, e stablished in 1930. Mean barley yields were 16-19% higher in the AER ( P less-than-or-equal-to 0.05) than in the CG system, and yield on eith er was about double that of the CBR. Within 9 yr, there was evidence o f increased total C, N, and P; available N, P and K, CEC; microbial bi omass, microbial respiration; and counts of bacteria, fungi, and mycor rhizae in the AER compared with the CG system. We conclude that biolog ical fixation of N by legumes can be used as the sole source of N for barley production on Luvisolic soils of low fertility such as the Bret on loam, without sacrificing yield or soil quality. Barley yields in t he AER (38% of the rotation time) exceeded those of barley grown under continuous cereal cropping. The soil resource was maintained or impro ved during a 10-yr period under AER compared to the CG or CBR systems. Further research is needed to discover the mechanisms involved in reg ulating biological activity and availability of plant nutrients other than N in the AER system.