Long-term yield patterns in barley-based cropping systems in Northern Syria. 2. The role of feed legumes

Abstract

Rotations of barley with feed legumes produce more biomass and crude protein than barley-fallow and continuous barley sequences, but scope remains to improve the potential value to farmers of feed legume-based systems. This paper summarizes 6-year results from two sites from 2-year rotations of barley with: narbon vetch (Vicia narbonensis) and lathyrus (Lathyrus sativus), each harvested mature; and common vetch (Vicia sativa), harvested by simulated green-grazing and mature, all in factorial combination with four NP fertilizer regimes applied biennially to the barley.Mean yield differences between rotations were quite small, but at the drier site the narbon vetch rotation was significantly superior in both total biomass and crop total nitrogen. Other results implied yield compensation between barley and legume phases: barley performance was relatively depressed at the wetter site after high-yielding narbon vetch but was relatively enhanced at both sites after green-grazed common vetch. Evidence from year-round soil-water monitoring suggests that the benefit following green grazing may have arisen, in part, from a small carry-over of profile moisture between crops not much inferior to that residual from a fallow year. Both crop phases responded strongly to biennial P fertilizer; and barley responded strongly to three rates of N-fertilizer, but a sometimes significant curvilinear component to this response reflected a tendency for grain yields to be depressed by added nitrogen in the driest years. But interactions between N-rates and rotations were not significant.It was concluded that narbon vetch may have greater potential than common vetch and lathyrus for mature harvest in drier areas, but its unsuitability for grazing green is a limitation. Flexibility of utilization is important, to accommodate the needs of different farmers and the exigencies of different seasons. The green-graze option has major potential where there is a demand for high-quality spring grazing; and indications that barley may be as productive after green-grazed vetch as after a year of fallow suggest an alternative approach for farmers who have previously avoided legumes in order to maximize barley production.