The four crop based cropping pattern (Lentil-Mungbean-T.Aus-T.Aman) was tested in the farmer's field of FSRD site, Kadamshahar, Godagari, Rajshahi during 2015-16 and 2016-17. The soil of the experimental plots belongs to Amnura series under AEZ 26. The soil of the experimental site was collected from two soil depth (0-15 cm and 15-30 cm) and analyzed. The experiment covered one hectare of land. Land was selected based on the discussion with local farmers, DAE personnel and available secondary information. The improved pattern (IP) Lentil-Mungbean-T.Aus-T.Aman (IP) was compared with farmers’ practice (FP) Boro- Fallow-T.Aman. The experiment was designed with two cropping patterns as a treatment and laid out in a randomized complete block design with six dispersed replications. In IP, lentil var. BARI Masur-6, mungbean var. BARI Mung-6, rice var. BRRI dhan48 and BRRI dhan57 were used for lentil, mungbean, T. Aus and T. Aman rice, respectively. In FP, rice var. BRRI dhan28 was used for Boro rice and Swarna for T. Aman rice in both the years. In Barind area, farmers normally used drought tolerant T. aman var. Swarna. The trial was started with mungbean crop and completed two crop cycles in two consecutive years. The rates of the fertilizers for different crops were calculated using soil test value based (STB) on high yield goal as per FRG (BARC, 2012). For mungbean and lentil, all the inorganic fertilizers were applied at the time of final land preparation. In case of T.Aus and T. Aman rice, all the fertilizers except urea were applied as basal. Urea was applied as top dressing in three equal splits at 10, 25 and 40 days after transplanting. All the crops were harvested at maturity from five spots with an area of 6.0 m2 each. Data on yield of various crops in sequences were recorded and converted to ton per hectare. The data of FP was recorded from adjacent farmers’ plots. Total system productivity was calculated as summation of individual (component) crop yield of each cropping cycle. The productivity of crop sequences was compared by calculating their economic rice equivalent yield (REY) using formula given by Ahlawat and Sharma (1993).
Apparent nutrient balance
Apparent nutrient balance was estimated considering the total amount of nutrient added to the soil through different sources and the total amount of nutrient uptake by the crop(s) (crops grain and their straw) each year. This calculation was valid particularly for P and K while calculating N balance, a 30% N loss have been assumed through different losses (like leaching, denitrification and volatilization loss etc). Apparent nutrient balance was expressed in kg ha-1 yr-1. The mean annual apparent N balance for the total pattern was calculated using the following formula:
Xa = (Xf+ Xr+ Xi+ Xb+Xcri) - Xrem
Where,
Xa = Apparent gain (+) or loss (-) of N (kg ha-1) Xf = N added through inorganic sources (kg ha-1) Xr = N added through rainfall (kg ha-1)
Xi = N added through irrigation water (kg ha-1) Xb= N added through BNF (kg ha-1)
Xcri= N added through crop residue incorporation (kg ha-1)
Xrem= N removed by crops and loss through different systems (kg ha-1). Apparent N balances were calculated from sequences.
The annual apparent P or K balance was calculated using the following simple equation:
Ya = (Yf+ Yr+ Yi +Ycri) - Yrem
Where,
Ya = Apparent gain (+) or loss (-) of nutrient (P or K) (kg ha-1) Yf = Nutrient (P or K) added through inorganic sources (kg ha-1) Yr = Nutrient (P or K) added through rainfall (kg ha-1)
Yi = Nutrient (P or K) added through irrigation water (kg ha-1)
Ycri= Nutrient (P or K) added through crop residue incorporation (kg ha-1) Yrem= Nutrient (P or K) removed by crops through different systems (kg ha-1).
Grain and straw samples of different crops were analyzed in the SRDI laboratory, Shyampur, Rajshahi determine the concentration of N, P and K. The data were analyzed statistically with open source software R (R Core Team, 2017).