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Notes:
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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.
This work was funded by the Comision Interministerial de Ciencia and Tecnologia (CICYT), AGR94-198 and AGF98-0261-C02; and the Instituto Nacional de Investigaciones Agrarias (INIA), PD96-029 projects. We also thank the Ministry of Education and Culture for funding the doctorate studies of P. Angas. |
