Site description and soils Field experiments were conducted for two consecutive years (winter season of 2014-15 and 2015-16) at two locations viz. (i) the research field of Regional Pulses Research Station (RPRS), Bangladesh Agricultural Research Institute (BARI), located in the moist monsoon climatic subtropical region of Madaripur (23°10′53″ N latitude and 90°11′28″ E longitude) at an elevation of 7.0 m above the sea level. The calcareous soils of Madaripur is medium high land with loamy texture which belongs to Gopalpur series (Soil taxonomy: Order-Inceptisols, SubGroup-Aquic Eutrochrepts) under the Low Ganges River Flood plain (Agro-Ecological Zone-12). Madaripur receives 1.0 to 83.0 mm rainfall which occurs from October to March. The mean minimum and maximum air temperatures during the period (October to March) of the Quddus et al. 133 experiments were 11.0 and 31.5°C, respectively. Average air temperature varied from 20.2 to 29.1°C during 2014-15 and 18.2 to 27.5°C during 2015-16. (ii) The Regional Agricultural Research Station (RARS) farm. RARS located in the Jashore (23.11°N latitude and 89.14°E longitude) lies at an elevation of 6.71 m above sea level. The land belongs to the High Ganges River Flood plain (Agro-Ecological Zone-11) and Gopalpur soil series (Soil taxonomy: Order-Inceptisols, Sub-Group-Aquic Eutrochrepts). The soils of Jashore are calcareous in nature having silt loam texture. The Jashore area receives average rainfall from 1.7 to 65.0 mm during October to March. The mean minimum and maximum air temperatures during the period (October to March) of the experiment were 9.30 and 30.6°C, respectively. Average air temperatures ranged from 16.6 to 24.5°C during 2014- 15 and 17.1 to 25.3°C during 2015-16. The initial soil samples (0-15 cm depth) of both locations have been analyzed.
fertilizer application The land was first opened by a tractor-operated chisel plough and then prepared thoroughly by ploughing with a power tiller followed by laddering and leveling. The clods were broken and the fields were made weed and stubbles free. Hence, the experiment was planned with sixteen (16) treatment combinations comprising four levels of Zn (0, 1.0, 2.0 and 3.0 kg ha-1) and four levels of B (0, 1.0, 1.5 and 2.0 kg ha-1) along with a blanket dose of other fertilizers of N, P, K and S at 12, 22, 30 and 10 kg ha-1, respectively. The treatment combinations were as T1 = Zn0B0; T2 = Zn0B1.0; T3 = Zn0B1.5; T4 = Zn0B2.0; T5 = Zn1.0B0; T6 = Zn1.0B1.0; T7 = Zn1.0B1.5; T8 = Zn1.0B2.0; T9 = Zn2.0B0; T10 = Zn2.0B1.0; T11 = Zn2.0B1.5; T12 = Zn2.0B2.0; T13 = Zn3.0B0; T14 = Zn3.0B1.0; T15 = Zn3.0B1.5; and T16 = Zn3.0B2.0. The experimental design was a split-plot with three replications. The unit plot size was 12 m2 (4 m × 3 m). Zinc and B were applied treatment-wise as Zinc sulphate (ZnSO4.7H2O) and Boric acid (H3BO3), respectively. Every plot received an equal amount of other fertilizers at N12 P22 K30 S10 kg ha-1 (FRG, 2012) as urea, TSP, MoP and gypsum during final plot preparation. The unit plots were separated from each other by an alley of 50 cm width. Three replicated blocks were alienated by the space of 1 m width.
Seed sowing and agronomic practices Seeds of a high yielding fieldpea variety (BARI Fieldpea1) were treated using the fungicide Provex 200 (at 2.5 g kg-1 seeds) before sowing for controlling of soil born diseases. Treated seeds were sown at 30 kg ha-1 on 09 November, 2014 and 07 November, 2015 at Madaripur and 12 November, 2014 and 09 November, 2015 at Jashore. Seeds were sown continuously in rows (10 rows/plot) maintaining row to row spacing of 30 cm. Hand weeding, as well as thining of seedlings, were done at 25 days after sowing (DAS) maintaining the distance of plant to plant 05 cm by making a total of 800 plants per plot (12 m2). Again, hand weeding was done at 50 DAS. The disease (powdery mildew) was control by spraying of Thiovit fungicide @ 2 g L-1 in two times at 10 days interval, starting from flowering stage and insects (pod borer and aphid) were controlled by spraying insecticide of Karate @ 0.2% during two times at podding stage interval of 10 days. Mature crop means fieldpea plants to be prostrate vines and the seed become hard containing 14-15% moisture (Oelke et al., 1991).
Data collection Number of nodules per plant was calculated at seedling, vegetative, flowering and podding stage at an interval of 15 days. During calculation 5 plants from each plot were selected randomly. Plants were smoothly uprooted and the soil from roots was removed carefully using tap water. The roots were then washed with distilled water, blotted with tissue paper and the number of nodules per plant was counted. Separated nodules were sliced into two pieces to observe the inside colour for nodules activity. The lightpink or red coloured nodules were considered as active. Regarding pods per plant, 10 mature plants of fieldpea were randomly selected and uprooted from the middle eight rows of each plot at the harvest time. Pods were detached from every plant and the number of pods per plant was counted and average calculated. Then seeds were separated from selected 10 plants in each plot. For stover yield (kg ha-1), mature plants were collected from two 1 m2 quadrates in each plot at harvest time. The harvested plants were brought to the threshing floor for sun dry and seeds were separated from stover with the help of bamboo stick. The sun dried stovers were weighed and recorded data were converted to kg ha-1. Rest of the matured plants (including border rows) of each plot were also harvested and brought to the threshing floor for sun drying and seeds were separated. The seed yield (kg ha1 ) was calculated based on whole plot (4 m× 3 m) technique. Thousand seed weight (g) was determined by the counting of 500 seeds randomly from each plot and weighing through electronic balance and converting it into 1000-seed weight adjusting at around10% moisture content (Seedburo 1200D Digital Moisture Tester Manual, USA).