Effect of Tillage Systems and Crop Residues on Soil Bulk Density and Chemical Properties under Corn (Zea mays L.) -Bean (Phaseolus vulgaris L.)

Management practices such as soil tillage can be used as a suitable alternative to reduce the crisis and increase the amount of organic carbon in the soil, along with the improvement of soil physicochemical properties. Long use of the conventional tillage system leads to reduced organic carbon content, soil destruction, reduced water penetration into the soil, and ultimately increased water erosion and wind. It has been established that disturbing the soil through tillage operations is not actually required to obtain good crop yields, and also a major portion of energy (25–30%) in agriculture is utilized for either field preparation or crop establishment, where conventional tillage is mostly followed. The rising cost of fuel and availability of effective package of practices for conservation tillage are now redefining tillage in Iran in recent years. However, the impact of conservation tillage on soil physical environment is not always positive and varies from one soil to the other and also between the cropping systems.Plant residues, by replacing or providing nutrients in the soil, maintain soil fertility, increase organic matter, water capacity, improve physical, chemical and biological properties creating diversity in management methods and different forms of exploiting resources. In other words, increasing agricultural diversity is one of the best and most effective ways to achieve sustainable production.The present investigation was therefore undertaken to determine the effects of tillage and crop residue management on soil bulk density and chemical properties in intercropping of corn and bean under Shahrekord's climatic conditions.

This study was conducted to evaluate the effects of different tillage levels and crop residue management on total nitrogen, organic carbon, available P and K, bulk density and carbon sequestration of soil compared to the beginning of the experiment. Hence, an experiment was performed using split- split plot based on a randomized complete block design with three replications in Agricultural Research Field of Shahrekord during 2016–2017. Tillage with three levels (conventional, minimum, and no-tillage) and four levels of crop residues (0, 30, 60, and 90% of straw yield of wheat) and five intercropping patterns including corn and bean sole cropping, corn and bean ratio with 2:2, 3:1 and 1:3 were considered as main, sub and sub-sub plots, respectively. Total Nitrogen content (TN), available P, available K, and bulk density were measured by the Kejldahl (Bremner, 1970) and Olsen methods (Olsen et al., 1954), flame photometry and Black (1965) procedures, respectively. Data analysis included the analysis of variance and mean comparisons using LSD which carried out using SAS software.

Increasing compaction of tillage with soil degradation mineral decomposition and plant residues reduced total nitrogen, organic carbon, available potassium and soil bulk density. The highest and the lowest available K were related to no-tillage treatment, 90% of crop residue and 2:2 ratio and conventional tillage treatment, sole cropping, and without crop residue respectively. The lowest soil bulk density related to conventional tillage, 90% residue, and 3:1 ratio. Conservation of plant residues through protective tillage over time will increase soil organic matter, which will reduce the bulk density of the soil. The highest and the lowest soil carbon sequestration were computed in no-tillage treatment, 90% of crop residue and 2:2 with 4154.33 kg.ha-1 and conventional tillage,without crop residue and bean sole cropping with 836.33 kg.ha-1, respectively.

Investigation showed that the no-tillage treatments and intercropping increased the efficiency of environmental resources and improved the soil nutrient, significantly. The highest organic carbon and total nitrogen were achieved 1:3 and 2:2 ratio, which is indicative of the excellence of intercropping compared to sole cropping. The amount of organic carbon has shown an increase in soil fertility using no-tillage with the conservation of residues and increase percent of bean in intercropping.