Tillage and N fertilization Effects on N dynamics and Barley yield under semiarid Mediterranean conditions

Reducing tillage and optimizing nitrogen fertilization are important strategies for soil and water conservation and sustainability of Mediterranean agricultural systems. These interacting practices can alter soil water and N availability, and thus affect N uptake, water use efficiency and crop yield. Three levels of N fertilization (zero, medium and high) and three tillage intensities (none, minimum and conventional tillage) were evaluated at three locations of the Ebro Valley in northeast Spain with different degrees of aridity and soil types (Guissona, Agramunt and Candasnos). Uptake of N by barley (Hordeum vulgare L.) was two to three times greater with N fertilization at locations with the best yield potential. Tillage increased soil mineral N content depending on location. Losses of N ranged from 30 to 80% of applied N each year and were encouraged by high N fertilization rates. Recovery of applied N ranged from 28 to 46.5%. N use efficiency ranged from 13 to 80 kg kg 1 N and was negatively affected by N fertilization up to 50% and by tillage up to 17%. It is thus found that farmer applications of N fertilizer can be reduced by up to 50%. No-till systems do not require increased amounts of N fertilizer for barley production in these areas. Only in wet years, higher yields are obtained in no till when some N fertilizer is applied. However, in dry years with scarce rainfall during autumn, N should not be applied in any tillage system. Reduced tillage and no till are suitable systems for improving yield and for optimal environmental and economical use of N in these Mediterranean conditions.

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