The experiment was conducted at Wheat Research Centre (WRC), Nashipur, Dinajpur, for 18-yrs with Wheat-Rice cropping system. The soil was sandy loam in texture (58.24% sand, 22% silt, 19.76% clay). At the beginning of the experiment, the soil was low in available N, medium in available P, low in exchangeable K, medium in available S and medium in Zn. The soil reaction was acidic in nature. The experiment was initiated with wheat during the 1997-98 wheat- growing season. The experiment was conducted in the fixed experimental site. The layout of the plots was kept undisturbed for growing the following rice. The experiment consisted of 9 treatments laid out in a randomized complete block design with 4 replications. The treatments for wheat were: control (T1), 100% NPKSZn (T2), 75% NPKSZn (T3), 75% NPKSZn+FYM (T4), 75% NPKSZn+FYM (T5), 75% NPKSZn (T6), 75% NPKSZn+PM (T7), 75% NPKSZn+PM (T8) and 75% NPKSZn (T9). In case of rice, the treatments were control (T1), 100% NPKSZn (T2), 75% NPKSZn (T3), 75% NPKSZn (T4), 75% NPKSZn+FYM (T5), 75% NPKSZn+FYM (T6), 75% NPKSZn (T7), 75% NPKSZn+PM (T8) and 75% NPKSZn+PM (T9). For rice, FYM (Farm yard manure) and PM (Poultry manure) were excluded from the treatment T4 and T7 to observe residual effects in rice of FYM and PM, respectively. FYM and PM were included to T6 and T9, respectively to see the direct effects of FYM and PM in rice. Wheat and rice received FYM and PM in the treatments T5 and T8, respectively to evaluate the effect of double application of organic manures per year for each of those crops. One hundred percent rates of recommended chemical fertilizers for both wheat and rice were 26 kg P, 33 kg K, 20 kg S and 4 kg Zn ha-1. However, the 100% recommended rate of nitrogen was 100 and 70 kg ha-1 for wheat and rice, respectively. Organic manures, both PM and FYM were incorporated @ the rate of 10t ha-1 to soil 4-5 and 15 days before seeding wheat and transplanted monsoon rice, respectively. Up to June 2015, the dry matter of FYM was added 94.43, 177.37 and 82.77 ton ha-1 in FYM as wheat, both crops and as rice treatments, respectively and the dry matter of PM was added 116.18, 218.82 and 108.39 ton ha-1 in PM as wheat, both crops and as rice treatments, respectively. The full dose of TSP, MP, gypsum, zinc oxide and two-third of urea were applied in wheat at the time of land preparation. The rest of urea was applied at crown root initiation (CRI) stage (18 days after sowing). The full amount of TSP, MP, gypsum and zinc oxide were applied in monsoon rice at the time of final land preparation. Urea were applied in three equal splits 15 days after transplanting, at maximum tillering and booting stages of the crop.
The surface soil (0-15 cm) was sampled at the beginning from the experimental site and from individual plots after completing 3, 9 12 and 15 cycles and chemically analyzed in laboratory to determine %total N, available P, exchangeable K, % organic matter and pH. Available S also determined after 12 crop cycles. Soils collected from individual plot after 15 crop cycles were analyzed for exchangeable Ca. Bulk density and percent porosity of surface soil (0-15 cm) of individual treatment were measured after 10 crop cycles. Data were statistically analyzed with MSTAT following the F-test and the mean comparisons were made by DMRT at 0.05% level