Experimental location: The experiment was conducted at the farmer’s field of Jamuna Char area of Gutail, Islampur in Jamalpur district of Bangladesh following randomized complete block design with three replications. The experimental site was of medium high land belonging to the agro-ecological zone Old Brahmaputra Floodplain under Agro-Ecological Zone 9 (UNDP & FAO, 1988). The experimental site is located at about 40 km North-West from Jamalpur district town. Planting materials Wheat (Triticum aestivum var. BARI Gom 26), garden pea (Pisum sativum var. BARI motorshuti 3) , grass pea (Lathyrus sativus var. BARI Khesari 2), lentil (Lens culinaris var. BARI masur 7), chickpea (Cicer arietinum var. BARI Chola 9) and mustard (Brassica napus var. BARI Sarisha 14) were used in this experiment. For spinach, local variety was used as there is no modern variety so far released by any organization in our country. Seed rates were 100, 30, 45, 7, 45 and 13 kg ha-1of wheat, lentil, chickpea, mustard; garden pea and grass pea respectively were used in this study.
Crop cultivation The main crop wheat was planted at 30 cm × continuous planting system to accommodate the component crop between two rows of wheat. Intercrops such as mustard, garden pea, grass pea, lentil, spinach and chickpea were included in the experiment. As a result, the whole treatment combination was T1= Sole wheat (100%) (30 cm × continuous), T2= 100% wheat + one row mustard in between two rows of wheat, T3= 100% wheat + one row garden pea in between two rows of wheat, T4= 100% wheat + one row grass pea in between two rows of wheat, T5= 100% wheat + one row lentil in between two rows of wheat, T6= 100% wheat + one row spinach in between two rows of wheat, T7= 100% wheat + one row chick pea in between two rows of wheat. The unit plot size was 5 m × 3 m. The sole crop wheat was sown on 05 November 2014 and on the same day the component crops were sown between two rows of wheat. Soil sample of the experimental plot was collected before set-up the experiment and analyzed in the laboratory. The texture of the soil was sandy loam to silt loam having pH 6.6 containing 1.79% organic matter. Fertilizers were applied in sole and intercrop plots at the rate of 45-15-36-7 .5-1.0-0.8 kg ha-1 N-P-K-S-Zn-B, respectively in the form of urea, triple super phosphate, muriate of potash, gypsum, zinc sulphate and boric acid (FRG, 2012). For intercrops, no additional fertilizers were applied. Two-third urea and all other fertilizers were applied as basal during final land preparation. The rest one-third urea was top-dressed after first irrigation. Gap filling was done where seeds were not germinated immediately after completion of 80% seedling emergence in the plot. This was done to maintain the optimum plant population. Two wedding was done in sole wheat. First was done at 30 and second was done at 45 days after sowing (DAS). Weeds that remained close to the wheat plants were removed by nirani. In case of all intercropping systems second weeding was not possible. On the basis of field conditions two irrigations was applied at 25 and 60 days after sowing. Flood irrigation was given at all times and after irrigation excess water was drained out as soon as possible.
Crop harvesting and data calculation: The sole crop wheat was harvested on 5th March, 2016 when at least 80% spikelet of each plot attained yellowing color maturity was recorded as days to maturity. Intercrops were harvested at different dates depending on their edible stages and maturity. Spinach, garden pea and grass pea were harvested two times while lentil, mustard and chickpea were harvested once a time depending on their maturity. Spinach was harvested at two times at 30 and 40 days after sowing while grass pea was harvested at 40 and 55 days after sowing as a vegetable and green forage. Weight of fresh garden pea, spinach and grass pea obtained from the whole plots at different harvests were recorded and summed up at the end of the crop’s life. The relative yield was obtained by dividing the intercrop yield of a crop with the respective sole crop yield of that crop using the formula (Dewit & Vander Bergh, 1965).
The relative yield of a crop = Yield of components crop / Yield of sole crop
Statistical analysis Collected data were analyzed statistically following analysis of variance technique as per design of the experiment. Computer package programs MSTAT and MS-Excel were used for statistical analysis. Mean separation was done at 5% level of probability following Least Significant Difference Test (LSD).