Barley yield and weed development as affected by crop sequence and tillage systems in a semi-arid environment

In order to monitor barley and weed development on a loamy sand soil subjected to different agronomic practices, field experiments were conducted for three growing seasons (1992-95) in a semi-arid agrosystem in central Spain. For eight years, independent plots were managed with three crop sequences: barley (Hordeum vulgare L.)-->vetch (Vicia sativa L.); barley--> sunflower (Helianthus annuus L.); and a barley monoculture. In all cases, two tillage systems were implemented: no-tillage and conventional tillage. In the years with standard rainfall (400 mm) an improvement in growth-related cultivation variables and yield components of barley were observed in plots under barley-->vetch rotation and/or conventional tillage. In drier conditions (<350 mm) the growth rate, crop yield and yield components of barley tended to improve under the no-tillage system. Barley-vetch rotation and/or conventional tillage increased nitrate-nitrogen (NO3-N) content in barley plants. Similar results were found for the concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium(Mg). In addition, the plots under crop rotation showed a weed biomass with a high concentration of N, K, and Ca in comparison with plots under monoculture. The lack of spring herbicide treatment in the no-tillage plots led to a 3-fold increase in weed density compared with the plots under conventional tillage.