Growth and yield attributes
The data on growth and yield attributes of blackgram (Table 1) indicated that the plant population per unit area differed for different crop establishment methods. The plant population/m
2 (32 plants) was significantly highest with sowing of blackgram by broadcasting 7-10 days prior to manual harvest of paddy, which was however comparable with sowing of blackgram by broadcasting 4-6 days prior to harvest of paddy with combine harvester. The crop establishment was poor with the no till seed drill sown on the day of paddy harvest. The results further indicated the residual moisture was lost rapidly under seed drill sown blackgram due to the deep furrow opened by the seed drill during sowing. This would have ultimately resulted in poor germination and establishment of blackgram. Similar to population/unit area, the plant height was also highest with sowing of blackgram by broadcasting 7-10 days followed by lifesaving irrigation on 30-35 DAS (29.3 cm). The microclimatic condition provided by the standing rice crop would have improved the growth of blackgram in the early stages and as a result, taller plants were observed with the particular treatment. Subsequently the life saving irrigation given on 30-35 DAS through mobile sprinkler increased the plant height in all the three crop establishment methods though it was non-significant. In seed drill sown blackgram, since the blackgram seeds were sown only after the harvest of paddy crop, the delay in establishment would be the reason for shorter plants under this treatment.
Amuthaselvi et al., (2019) also observed that the plant population per unite area was higher in broadcasting method as compared to seed drill sown in rice fallow blackgram.
Sowing of blackgram by broadcasting 7-10 days before the manual harvest of paddy followed by lifesaving irrigation on 30-35 DAS had the highest number of pods/plant (20.6); however it was onpar with other two crop establishment methods followed by life saving irrigation. The number of pods per plant did not vary among the different crop establishment methods as even lesser population per unit area had favoured the per plant yield parameters. The reason might be due to less competition between the plants where the feeding zone per plant was more. No significant variation among the different treatments was observed for number of seeds per pod.
Grain yield
Different crop establishment methods and life saving irrigation at critical stages significantly altered the grain yield of blackgram (Table 1). Sowing of blackgram by broadcasting 7-10 days before the manual harvest of paddy followed by life saving irrigation on 30-35 DAS produced higher grain yield of 875 kg ha
-1, which was 32.1% higher than blackgram sown with seed drill followed by life saving irrigation. However it was onpar with sowing of blackgram by broadcasting 4-6 days before the harvest of paddy with combine harvester followed by life saving irrigation. The optimum population maintained and moisture availability for a longer period due to earlier sowing in the blackgram sown 7-10 days before the harvest of paddy and life saving irrigation at 50 per cent flowering stage had resulted in more number of pods per plant and 100 seed weight. High grain yield due to more of pods per plant was also earlier reported by
Ramesh et al., (2016) in rice fallow blackgram and
Subrahmaniyan et al., (1999) and
Kalaiselvan et al. (2001) in groundnut.
Soil moisture content
The moisture percentage on the day of sowing black gram ranged from 32.78 to 34.76 % in 0-5 cm depth, 31.02 to 33.83% in 5-10 cm depth and 30.91 to 33.68% in 10-15 cm depth across the treatments (Fig 1). The moisture level at surface layer (0-5 cm) was highest as compared to subsurface layer due to the last irrigation impounded for paddy crop. Among the different treatments, irrespective of the depth, the soil moisture was highest with blackgram sown 7-10 days before the manual harvest of paddy on the day of blackgram sowing (34.76%). However on 45 DAS, the soil moisture at the surface layer was highest with blackgram sown 7-10 days before the manual harvest of paddy followed by lifesaving irrigation on 30-35 DAS (20.89%). Moisture content was comparable with blackgram sown 4-6 days before the harvest of paddy with combined harvester followed by lifesaving irrigation on 30-35 DAS (19.26%). The life saving micro sprinkler irrigation to a depth of 10 mm would have improved the soil moisture content at the surface layer though it did not influence the moisture content in the sub surface layer to a greater extent.
Senthil Kumar et al., (2018) also observed increase in soil moisture due to sprinkler irrigation in blackgram. Irrespective of the days of observation and depth, the lowest soil moisture was observed with balckgram sown with the seed drill due to the V shape furrow opened during the sowing, which paved way for rapid depletion of moisture as compared to other treatments.
Economic analysis
Blackgram sown 7-10 days before the manual harvest of paddy followed by lifesaving irrigation on 30-35 DAS had the highest net return (₹ 37013 ha
-1) and BCR of 3.39 (Table 2), which was closely followed by blackgram sown 4-6 days before the harvest of paddy with combined harvester followed by lifesaving irrigation on 30-35 DAS (₹ 35153 ha
-1 and 3.27). The additional net return obtained by one life saving irrigation at flowering stage ranged from ₹ 6968 ha
-1 to ₹ 14168 ha
-1. The net return and BCR was lowest with blackgram sown with seed drill either with life saving irrigation or without life saving irrigation in the respective group of treatments.
Thus, sowing of blackgram 4-6 days before the harvest of paddy with one life saving irrigation with micro sprinkler on 30-35 DAS by utilizing the water harvested in the farm pond would result in similar yield that of blackgram sown 7-10 days before the manual harvest of paddy followed by one life saving irrigation with micro sprinkler on 30-35 DAS.