Evaluation of the Effect of Rotation and Application Rate of Nitrogen on Yield, Yield Components and Nitrogen Efficiency Indexes in wheat

There are about 160 species in Brassica genus, which are mostly annuals and biennials. The plants in this genus have potential for fodder uses. The progress in plant breeding science has produced new crop varieties for oil and forage usages. Perko varieties are derived from crosses between tetraploid plants of winter rapeseed (Brassica napus L.Var. napus) and Chinese cabbage (Brassica campestris L. var. sensulato). The new plants are superior to their parents from various aspects. Buko varieties are new amphiploid plants obtained by crossing between tetraploid winter rapeseed, Chinese cabbage and turnips (Brassica campestris L. var. Rapa). Oilseed radish with scientific name (Raphanus sativus L.) is a genus of the Brassica and consumption, oil, green manure, feed and fodder (24). This plant in many countries, including Canada, is cultivated in gardens as cover crop. Oilseed radish grows fast in the cool seasons. Ramtil (Guizotia abyssinica) belongs to the Compositae family, Phasilia (Phaceli atanacetifolia L.) belongs to Boraginaceae family and clover is from Fabaceae family that is grown for feeding purposes.

A field experiment was conducted from 2011 to 2012 in the Karezan region of Ilam, Iran (42º33′N, 33º46′E) on a silty-clay with low organic carbon (1.26%) and slightly alkaline soil (pH=7.9). This site is characterized as temperate climate with 370 mm annual precipitation. The experiment was arranged in a split plot based on randomized complete block design with four replications. The main plots consisted of 6 pre-sowing plant treatments (control, Perko PVH, Buko, Clover and Oilseed radish and combination of three plants Ramtil, Phaselia andclover), and sub plots covered four N fertilizer rates including no fertilizer N (Control), 50% lower than recommended N rate, recommended N rate and 50% more than recommended N rate. Winter wheat (cv. Pishtaz) was sown on mid-November with the row spacing of 15 cm and a seeding rate of 200 kg ha-1. Soil samples were collected after harvest of each crop from 0 to 30 cm and 31 to 60 cm soil depths using a soil auger. Wheat grain yield (according to 14% moisture) obtained by harvesting the central area of 3 in 10 m in each plot. Yield components were determined from two randomly selected areas (2m2) within each plot. Plant samples collected at harvest were separated into grain and straw and oven-dried at 60˚C for 72hr. Biomass and grain sub samples analyzed for total N content using a micro-Kjeldahl digestion with sulfuric acid. The terminology of N efficiency parameters was considered according to Delogu et al, (11) and Lopez-Bellido & Lopez-Bellido, (22), Rahimizadeh et al. (30), Limon-Ortega et al. (20) methods.

The results showed that there were highly significant differences (P ≤ 0.01) in forage yield. There were also significant differences (P ≤ 0.05) in total dry weight, protein content and protein yield between treatments. Perko varieties produced higher fresh and dry matter yield with 69,586 (kg ha-1) and 7147 (kg ha-1), respectively compared to other varieties. Buko varieties showed greater protein percentage with 23.36 compared to the rest of the varieties. The highest and lowest grain yield, with 8345, and 4491 (kg ha-1) were obtained for Buko; wheat rotation and fallow, wheat rotation, respectively. The highest and lowest nitrogen uptake was obtained for Buko; wheat and clover, wheat rotation, respectively. The differences between the rotations were significant for various agronomic nitrogen efficiency. The rotation of oilseed radish and wheat showed greater nitrogen economic performance with 36.20 kg ha-1. By increasing nitrogen rate agronomic performance decreased with the exception in fallow- wheat. Physiological efficiency of nitrogen in fallow-wheat rotation was more than 39 (kg kg-1) of nitrogen. The maximum efficiency of nitrogen recovery was obtained for oilseed radish: wheat and Perko PVH; wheat rotations with 45% and 36%, respectively. The highest nitrogen harvest index was observed in Buko; wheat rotation: (86.5%), and Perko: wheat (85%) and the lowest nitrogen harvest index was in fallow; wheat (79.28%).

The results showed that Perko; wheat and Buko; wheat rotations due to the higher economic performance in the region were appropriate rotations and were recommended for the study area.