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Crop Establishment Methods and Moisture Mitigation Practices in Rice Fallow Blackgram for Productivity Enhancement in Cauvery Delta Zone of Tamil Nadu
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First Online 09-11-2020|
Methods: The studies were conducted during post rainy seasons of 2015-16 to 2017-18. with six treatments viz., T1 - Sowing blackgram by broadcasting 7-10 days prior to manual harvest of paddy, T2 - Sowing blackgram by no till seed drill on the day of harvest of paddy, T3 - Sowing blackgram by broadcasting 4-6 days prior to harvest of paddy by combine harvester, T4 - T1 + Life saving irrigation with mobile sprinkler once at 30-35 DAS, T5 -T2 + Life saving irrigation with mobile sprinkler once at 30-35 DAS, T6 -T3 + Life saving irrigation with mobile sprinkler once at 30-35 DAS.
Result: The results indicated that higher grain yield of 875 kg ha-1 was obtained with blackgram sown 7-10 days prior to manual harvest of paddy plus life saving irrigation on 30-35 DAS with mobile sprinkler using farm pond water, which was 31.6% higher than that of blackgram sowing with no till seed drill. The study also indicated that farm pond dug at an area of 100 m3 would be sufficient to irrigate 1 ha of blackgram through mobile sprinkler once at flowering stage (30-35 DAS by which the net return could be increased by ₹ 61416 ha-1.
The productivity of rice fallow blackgram is generally very low due to various biotic and abiotic stresses, poor crop management practices and socio-economic constraints (Behra et al., 2014). Soil and water are the two major limiting factors which lead to low productivity in rice fallow blackgram. Since irrigation is withdrawn 10-15 days before the harvest of rice crop, the moisture content in the soil decline rapidly with advancement of crop period. Especially from the second fortnight of February due to rise in temperature, the crop faces drought during flowering and pod formation stages which eventually resulted in poor yield.
If irrigation water is available, one light irrigation at pre flowering stage i.e., 30-35 days after sowing would be helpful in evading the terminal moisture stress and augment the grain yield in rice fallow pulses (Gupta et al., 2016). However flood irrigation is not advisable as the inundation of water in the cracked deep clayey soil would results in wilting of pulses. Hence life saving supplemental irrigations through mobile sprinklers with the use of stored water would be a viable strategy to increase the productivity in rice fallow situations (Gupta et al., 2016).
Maintenance of adequate plant population is a prerequisite to maximise returns from rice fallow pulse cultivation. Manual broadcasting 7-10 days prior to harvest of paddy at waxy soil moisture condition is the conventional practice (Ramesh et al., 2016). Uneven germination, population and distribution of plants are the common constraints associated. Unlike manual harvest, machine harvesting of paddy damages the establishing pulse plants due to the trampling effect of wheels on field traverse. With wider adoption of mechanised harvesting, it has emerged as a major abiotic stress in rice fallow cultivation. Under such circumstances, strategies should be worked out to improve crop productivity which should compensate the yield loss from the damaged crop. Hence to overcome the confronting issues, the present study was conducted to evaluate a moisture stress mitigating and crop establishment methods to increase the rice fallow blackgram productivity.
MATERIALS AND METHODS
A manual drawn single row seed drill (IIPR prototype) was employed to place the seeds in the manually harvested fields with an inter row spacing of one feet apart (T2). The sowing was taken up immediately after the harvest of paddy to avoid soil moisture loss. Seeds fell continuously into a V shaped furrow (7.5 cm depth) opened by the disc type wheel of the seed drill. A farm pond with a dimension of 15 m (Length) × 7 m (Breadth) × 2 m (Depth) was dug before the onset of monsoon to harvest the rainwater near the experimental field. The storage capacity was 210000 liters of water (210 m3). The effective storage was only 50% in the month of February when the irrigation was done (105000 litres). Thus, even after the cessation of North east monsoon, the water harvested and stored in the farm pond was sufficient for life saving irrigation. The portable mobile sprinkler was used to irrigate the crop in which the discharge rate was 80 liters/minute and for life saving irrigation with mobile sprinkler once at 30-35 DAS, 1,00,000 lakh litres of water was utilized to irrigate 1 ha cm depth, The data on growth and yield attributes were observed at the time of harvest. The seed yield was measured as total yield per plot and transformed to kg ha-1. Assessments on soil profile moisture depletion were calculated with gravimetric method taking soil cores at 0-5, 5-10 and 10-15 cm on the day of sowing, 30 DAS, 45 DAS and at harvest. The data were analyzed statistically as per the method suggested by Gomez and Gomez (1984).
RESULTS AND DISCUSSION
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/m2 (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.
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.
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.
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