Growth, yield and water productivity of barley (Hordeum vulgare L.) affected by tillage and N fertilization in Mediterranean semiarid, rainfed conditions of Spain
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In dryland agricultural systems of the Mediterranean area, the amount and variability of the rainfall are the main constraints to crop yield. Soil management through tillage and rational use of N fertilization can improve the performance of crops through improved use of available water and increased use efficiency. Field experiments were carried out at three locations differing in degree of aridity (Guissona, Agramunt and Candasnos) in the Ebro Valley in Northeast Spain during three growing seasons. Yield and water-use efficiency (WUE) of barley, the predominant crop in the area, were examined under three levels of N fertilization (zero, medium and high) and three soil management systems (no tillage (NT), minimum or reduced (MT) and conventional tillage (CT)). Soil water content, total crop dry matter, leaf area, yield and yield components were measured during consecutive crop cycles. In general, both levels of added nitrogen, increased the yield to about 30% above zero nitrogen. Grain number increased with N fertilization and determined the level of yield response. At two locations (Guissona and Agramunt), a positive effect of MTor NTwas observed under dry conditions. Yield (up to 60%) and WUE (up to 50%) were reduced by tillage. In the driest location of Candasnos, where a better response to reduced tillage (MT and NT) was expected, the WUEs for grain yield were low for all treatments (between 2.4 and 6.5 kg ha 1 mm 1 ) and the best crop performance was obtained in tilled treatments. Negative effects on yield were caused by the pests Mayetiola mimeuri Mesnil and Tetramesa tritici (Fitch), when stubble residues remained without tillage management. The use of conservation tillage in this specific Northeast area of the Ebro Valley improved the yield of barley and its WUE. Nitrogen fertilization in this area could be reduced to levels lower that those currently used by farmers. This reduction could be greater with increased tillage intensity. No additional N fertilizer was needed when under conservation tillage.