Effect of green manure and inorganic fertilizers on soil fertility, light extinction coefficient and grain yield of wheat cv. Chamran

In order to evaluate the effect of green gram (Vigna radiata) sowing date as a green manure in combination with different rates of nitrogen (N) and phosphorous (P) fertilizers on wheat grain yield and light extinction coefficient, a field experiment was conducted in Dezful during 2008-2009. The experiment was split-plot factorial based on RCBD with three replications. Main plot consisted of green gram sowing dates were 30th June and 10th August, besides to fallow and three rates of N (0, 60 and 120 kg ha-1) and P (0, 45 and 90 kg ha-1) were in sub-plots. Results indicated that the application of green manure increased soil organic matter and inorganic nutrients. The highest light extinction coefficient (K) found on 30th June. A significant increase in nitrogen rate led to more light extinction coefficient because of  higher LAI. In comparison to fallow treatment, the green manure sowing dates on 30th June and 10th August led to more grain yield by 15.3% and 3.1% respectively. Delaying in green gram sowing date reduced the benefit effects of the green manure in wheat grain yield. Generally, the results of this investigation showed that, sowing green gram as a green manure on 3th July has significantly increased wheat grain yield compared with fallow treatments. In green manure applied plots, wheat grain yield in 60 kg N ha-1 and 45 kg P ha-1 was higher than 120 kg N ha-1 and 90 kg P ha-1 under fallow conditions. The higher grain per unit area and biological yield in green gram residue incorporated plots influenced higher wheat grain yield than under fallow.