There have been a limited number of studies about the long-term impact of direct drilling (DD) on soil properties and legume yields for vertisol of southern Spain. In this work, we assessed the influence of DD and conventional tillage (CT) systems in a long-term trial under dry farming with legume, such as chickpeas (Cicer arietinum L.), broad bean (Vicia fafa L.), vetch (Vicia sativa L.) field pea (Pisum sativum L.), yields, and on soil chemical properties related to fertility (i.e., pH, soil organic carbon, phosphorus, potassium, calcium, magnesium, and the cation exchange capacity [CEC]) in a heavy clay soil. Direct drilling resulted in significantly (P ≤ 0.05) greater soil organic C (12 g kg−1) in the surface horizon (0-10 cm) of soil, 25% greater than CT (9.5 g kg−1). After 22 years of cropping, a significantly larger amount (P ≤ 0.05) of available phosphorus and exchangeable potassium was found in the surface horizon (0-10 cm) under DD compared with CT, whereas the extractable calcium content was higher in CT (600 mg kg−1) than in DD (500 mg kg−1). Irrespective of the tillage, the CEC (0.52 molc kg−1) had high values, indicating the good fertility level of the soil used in the experiment. The high CEC of this soil related to the presence large amounts of smectitic clay. Even under these conditions, DD can improve fertility levels. In general, the changes in soil chemical properties did not result in significant differences (P ≤ 0.05) in legume yields. However, the evolutions of the mean yields behaved better under DD than with CT, with a higher harvest ratio higher in DD (1.26 Mg ha−1, 118%) compared with CT (1.07 Mg ha−1, 100%) and producing approximately 15% more during the period. The DD/CT yield ratio increase as the annual rainfall did, indicating the more efficient water use of DD under dry farming in this soil.
1Department of Agronomy, University of Córdoba, Avenida Menéndez Pidal s/n, Apartado 3048, 14080 Córdoba, Spain. Dr. Bravo is corresponding author. E-mail: firstname.lastname@example.org
2Centre for the Study of Tropical Agroecology, Simón Rodríguez University, Apartado 47295, Caracas 1041-4, Venezuela.
3Department of Agronomy and Crops Production, IAS, CSIC, Apartado 4084, 14080 Córdoba, Spain.
4Area of Ecological Production and Natural Resources, IFAPA, Alameda del Obispo, Apartado 3092, 14080 Córdoba, Spain.
5Tomejil Experiment Station, IFAPA, Carmona, Seville, Spain.
6Department of Agroforestal Sciences, University of Seville, Road Seville-Utrera, km 1 41o13, Seville, Spain.
Received Sep. 20, 2005; accepted Nov. 1, 2006.