Residual Effect of Nitrogen and Phosphorus Fertilizers in Faba Bean Field on Yield in Faba Bean- Rice Cropping System in Guilan

Guilan province is a suitable area for growing second crop after rice in autumn. Growing a crop in a field of rice after it is harvested in addition to creation of job and increasing farmer’s income, can be used to produce a winter crop for the second six months of year. One of the most consequences of producing one or two crops is to conserve water and soil resources and reduces pollution caused by excessive chemical inputs and also maintaining and improving soil fertility in the long term. To investigate the effect of remains of fertilizers used in faba- bean on rice yield in faba bean- rice cropping system a research concering growing two crops in one year, namly rice var. Hashemi (June- September) and a second crop, faba bean var. Barkat (November- May) was performed with 15 fertilizer treatments for faba bean in the form of a factorial randomized complete block design with three replications in the Research Field of Rice Institute of Iran during years of 2012- 2015 (growing two crops of rice and three crops of faba bean). Experimental factors for faba bean consisted of five nitrogen rates (0, 25, 50, 75 and 100 kg.ha-1 N) from urea and three phosphorus levels (0, 50 and 100 kg.ha-1 P) from triple superphosphate fertilizer. The results showed that faba bean yield increased up to 2003 kg.ha-1 and 285 kg.ha-1 by increasing nitrogen and phosphorus levels respectively. The highest seed yield (4833.8 kg.ha-1) was observed in the treatment N100P100 where the difference with that of N100P50 treatment (4744.5 kg.ha-1) was non significant. The results also showed that nitrogen and phosphorus used in faba bean increased soil nitrogen by 0.147% to 0.178% and 0.209% and soil phosphorus by 24.2 ppm to 40.59 and 37.51 ppm in the first and second years of rice production, respectively. The average yield of two- cycle production of rice (without chemical fertilizers and after faba bean cultivation) was about 2770.95 kg.ha-1.