Influence of Conservation Tillage on some Soil Physical Properties and Crop Yield in Vetch-Wheat Rotation in Dryland Cold Region

Introduction Winter wheat is an important, well-adapted grain crop under dryland condition of the northwest of Iran. Soil water is the most limiting resource for crop growth in dryland areas. Therefore, farmers need to use crop residues and minimum tillage to control the soil erosion and effectively store and to use the limited precipitation received for crop production. Crop rotation and tillage system could affect crop yield due to their effects on water conservation and soil chemical and physical properties. Galantini et al., (2000) studied the effect of crop rotation on wheat productivity in the Pampean semi-arid region of Argentina and found that a wheat–vetch (Vicia sativa L.) rotation resulted in higher yield and protein content, and greater yield components than the other rotations.Payne et al. (2000) stated that where precipitation amount is marginal (400 mm), dry field pea offers a potential alternative to summer fallowing. The purpose of this study was to identify the optimal tillage system for increasing crop productivity in a vetch–wheat rotation in dryland farming of the northwest of Iran. Materials and Methods The field experiment was carried out from 2010 to 2014 at the Dryland Agricultural Research Station (latitude37° 12´N; longitude 46◦20´E; 1730 m a.s.l.), 25 km east of Maragheh, East Azerbaijan Province, Iran. The long-term (10 years) average precipitation, temperature and relative humidity of the station are 336.5 mm, 9.4 ◦C and 47.5%, respectively. The soil (Fine Mixed, Mesic, Vertic Calcixerepts, USDA system; Calcisols, FAO system) at the study site had a clay loam texture in the 0–15 cm surface layer and a clay texture in the 15–80 cm depth. This study was conducted in vetch (Vicia pannonica)- wheat (Triticum aestivum L.) rotation. The experiment was arranged in a randomized complete block design with four replications. The tillage treatments consisted of (1) conventional tillage: moldboard plowing followed by one pass of a disk harrow (CT); (2) reduced tillage:chisel packer (CH); (3) minimum tillage: Stubble mulch cultivator (MT); and (4) no-till (NT) with retained previous crop residue. At beginning prior to the tillage operation, only wheat stubble was present on the soil surface. A uniform tillage treatment was applied to all plots using a chisel packer in October. A shallow tillage was also performed using a tandem disk harrow just prior to winter vetch planting. In the second, third, fourth and fifth years, the tillage treatments for the vetch and wheat planting were similar. A winter wheat cultivar (Azar 2) was sown 6 cm depth at a rate of 350 seeds per square meter with an Alvand conventional and Baldan NT 250 no-till drill. Vetch cultivar Golsefied was drilled 8 cm depth at a seeding rate of 85 kg ha−1 using Alvand drill. The following parameters were measured: heads of wheat per square meter, 1000-kernel weight, kernels per head, head length, plant height, and wheat grain yield. Grain yield was obtained with a plot combine harvester. The dry matter content was determined and yield corrected to a standard moisture content of 130 g kg−1. Rain use efficiency (RUE) was calculated by dividing dry weight of grain yield by growing season precipitation. Soil water content and dry bulk density were measured gravimetrically (drying method, w/w) in cropping seasons. Results and Discussion Conservation tillage treatments resulted in water saving in soil layers. In both stages of soil sampling, the most soil moisture variability to initial state was observed in plots which planted as no-tillage. The moisture variability of no-tillage system was 23.4% higher than that of conventional tillage system at 10-20 cm soil layer in flowering stage of wheat. Effect of treatments on soil bulk density in different soil depths illustrated that conservation tillage can reduce soil bulk density during four years. According to the results of this study the overall infiltration in no-tillage was 1.58 times more than that of conventional tillage system. Yields under no-tillage and reduced tillage were higher (4% and 6% respectively) than conventional tillage. Grain yields under direct drilling were similar to those obtained using the reduced-tillage (Chisel packer) system. Conclusions Based on the results of a 4-year field study on a dryland production system in the northwestern cold continental climate of Iran, minimum- or no-till winter wheat crop production in a vetch–wheat rotation were the most efficient soil management practice from the standpoint of grain yield production and rain use efficiency. Overall, in this study, the no-tillage treatment is proposed as the best treatment in terms of grain and biomass yields and mechanical properties of soil.