Responses of sunflower to traditional and conservation tillage under rainfed conditions in southern Spain

摘要

Nitrogen (N) availability is one of the most crucial aspects of conservation tillage. Therefore, the advent of this system makes it advisable to study nutritional crop response for given site-specific environments. We have studied for three years (1993, 1995 and 1997) the effects of a traditional tillage (TT) and a conservation, reduced tillage (CT) system on the growth and nutrition of a sunflower crop, in a wheat (Triticum aestivum L.)-sunflower (Helianthus annuus L.) rotation, established under rainfed agriculture in a sandy clay loam soil (Xerofluvent) of southern Spain. The TT method consisted mainly of the use of mouldboard ploughing, and CT was characterized by leaving the crop residues on the soil surface as mulch, chiselling after wheat and disc harrowing after sunflower, before sowing wheat. Sunflower, the crop studied, was not fertilized. In both tillage treatments, seedlings (separated into shoots and roots) and plants at flowering were collected for analysis. Plant growth and yield were also determined. After harvesting in 1995 and 1997 soil samples were collected (0-5 and 5-30 cm depth) for oxidizable organic matter (OM) and available nutrients analysis. For the third crop, soil nitrate nitrogen (NO3-N) was determined (0-10 and 10-30 cm depth) before sowing and four times after sowing. The CT method usually increased OM and N, and other nutrient contents in the top soil (0-5 cm), in relation to TT. However, for the third crop, soil NO3-N at the seedling stage was similar in both treatments (within the range 25-42 kg ha-1, 0-30 cm depth). Nevertheless, sunflower plants showed better early growth and higher N concentration in TT than in CT. Concentration and total content of NO3-N of both shoots and roots in the seedlings of the third sunflower crop were also greater in TT (more than 50% and 100%, respectively). This seems to show that factors other than N-availability could affect the early plant nutrition and growth. These nutritional differences disappeared later (early flowering), except in the second sunflower crop (1995), which could not complete normal growth in the TT treatment due to the severe drought of that year. The lower early growth and N-uptake in CT did not affect either yield or seed quality for the three years studied. It is concluded that CT was effective in increasing OM and N in the top soil, that CT greatly reduced early growth and N uptake of the crop but favoured yield formation during drought. Those are important aspects to be considered in the long-term.