The Effect of cropping systems management and wheat residues on grain yield and efficiency indices of nitrogen and phosphor in autumnal rapeseed

The issue of maximizing crop yields through excessive consumption of chemical inputs and high costs in the production of these products has led agricultural experts and analysts find a suitable way to integrate technology and conserve natural resources in order to create a favorable environment for the optimal use of available resources, reduce environmental problems and increase yields per unit area and provide greater profitability in agriculture (Ratek et al., 2004). On the other hand, Iran's location in arid and semi-arid climates has caused the soil of most areas to be poor in organic matter and this is one of the problems that can be effective in reducing performance and increasing production costs (Chegni et al., 2014). So it seems maintaining of sufficient amount of plant residues in the soils is an effective way to overcome the soil quality threats. This research was carried out with the aim of investigating the effects of different cropping systems management and wheat residues on grain yield and efficiency indices of nitrogen and phosphor in autumnal rapeseed. The experiment was conducted as strip split plot based on randomized complete block designs in three replications in 2015-2016 in two locations (Sarableh and Roumeshgan) in southern west of Iran. The first factor was cropping systems in three levels as low input (one disk + 25% of plant nutrient requirement as fertilizer + two stages manual weed control), Mid input (one plowing + one disk+ 50% of plant nutrient requirement as fertilizer+one stage manually and one stage using herbicide to weeds control) and full input (two plowing +two disk + 100% of plant nutrient requirement as fertilizer+ two stages herbicide to weeds control). The second factor was wheat residues managements in four levels of 0 as control, 2, 4 and 6 t.ha-1. The required fertilizer was calculated based on the results of soil analysis so that 100 kg of superphosphate and 200 kg of urea in Romeshgan and 150 kg of superphosphate and 300 kg of urea in Sarablah were required. To control weeds in the low input system, two stages of mechanical weeding in 7 and 45 days after planting, in the medium input system, one stage of chemical control (terflan) at the same time as planting and one stage of mechanical weeding in 45 days after planting, and in the full input system, two stages of spraying simultaneously with planting (Terflan) and 45 days after planting (Lontrol + Supergalant) were performed. Finally, after calculating grain and biological yield, uptake efficiency, utilization efficiency and nutrient use efficiency were determined.After testing the uniformity of variance using Bartlett test, the combined analysis of data was performed by SAS 9.1 software.Results and DiscussionThe results showed that in low input management with increasing wheat residues, the phosphor and nitrogen use efficiency was decreased so that in the treatments of four and six tons of residues per hectare compared to non-residues, respectively, nitrogen productivity of 15 and 22 percent and phosphor productivity of 15 and 20 percent were significantly decreased. With the move of crop system management towards high input management, the positive effect of low residue levels on nutrient use efficiency was determined so that in high input management, the highest efficiency of nitrogen and phosphorus consumption was obtained with 12.3 kg of grain per kg of nitrogen and 30.3 kg of grain per kg of phosphorus from treatments of four tons of wheat residues, respectively. The results also indicated that in all treatments, the effect of nitrogen and phosphorus uptake efficiency was higher than their utilization efficiency on the use efficiency of each of these nutrients. Therefore, the management of crop systems based on increasing the uptake efficiency of each nutrient in rapeseed cultivation can play a decisive role in increasing yield.In general, the results showed that with increasing the entrance of inputs and crop system management the uptake and use efficiency of nitrogen and phosphorus increased, but nutrient utilization efficiency was maximized in medium input management. It was also found that with increasing the application of wheat residues to the soil, the efficiency of uptake and use of nitrogen and phosphorus nutrients indicated a decreasing trend.