Farmers’ participatory SSNM experiment was conducted on 72 farmers’ fields in Low Ganges River Floodplain of Agro - Ecological Zone (AEZ) -12 of Bangladesh. The common cropping pattern was Boro (January to May) - fallow – T.aman (July to November). Soils of the region are silt loams and silty clay loams on the ridges and silty clay loam to heavy clays on lower sites. Five fertilizer treatments, i.e., nitrogen omission (PK), phosphorus omission (NK), potassium omission (NP), balanced fertilizer (NPK) and farmers’ practice (FP) were used.
Two sites (Site-I and Site-II) within each district (Faridpur, Gopalgonj and Madaripur) were selected for trial. From six sites, four farmers (each farmer represented one replication) were selected from each of high, medium or low land. So, selected numbers of farmer were 24 (12 from site-I and 12 from site-II) from each district. The experimental design was split-split plot (mentioned main and sub plot) with four replications. Farmers cultivated BRRI dhan29 in Faridpur and Gopalgonj but BRRI dhan28 in Madaripur district. The age of seedlings for transplanting varied from 40 to 55 days. Transplanting time ranged from mid-January to last week of February. Blanket doses of other nutrients were included in all treatments to prevent deficiencies other than nitrogen (N), phosphorus (P), or potassium (K). In this trial, N, P and K were used at 147, 20 and 50 kg ha-1 in the form of urea, triple super phosphate (TSP) and muriate of potash (MoP). The TSP and MoP were applied during final land preparation but urea was top-dressed in three splits (15, 30 and 50 days after transplanting). Intercultural operation and irrigations were similar in all locations. Monitoring was done through frequent field visits and keeping close contact with respective farmers during the crop-growing period.
Calculation of Optimum Fertilizer Rates
Optimum N, P and K doses were calculated following Driessen (1996):
N = [(YNPK – YPK)/ NU] ´ 18 [1]
P = [(YNPK – YNK)/ PU] ´ 2.5 [2]
K = [(YNPK –YNP)/ KU] ´ 20 [3]
Where, YNPK = yield in NPK plots, YPK = yield in N omission plot, YNK = yield in P omission plot, YNP = yield in K omission plot, NU =N-use efficiency (40%), PU = P-use efficiency (60%), and KU = K-use efficiency (80%) (BRRI, 2004).
Grain yield was harvested at maturity and was adjusted to 14% moisture content [GMK-303RS (G-WON HITECH Co., LTD, Korea)] was used. Crop data were analyzed using the CropStat 7.2 software (IRRI, 2015).