Resilient rice based cropping systems for lowlands

Abstract

The study entitled “Resilient rice based cropping systems for lowlands” was carried out at the Department of Agronomy, College of Agriculture, Vellayani during the period from 2019-2023. The major objectives of the study were to evaluate the performance, in terms of yield and economics, of different rice based cropping systems in lowlands, investigate their impact on weed dynamics, soil health and carbon dioxide emission, and assess the residual effect on the succeeding virippu rice crop. The investigation comprised two experiments viz. Experiment I: Performance of different rice based cropping systems in lowlands and their impact on the weed dynamics, soil health and carbon dioxide emission and Experiment II: Residual effect of rice based cropping systems on the succeeding virippu rice crop. The field experiments were carried out at the Integrated Farming System Research Station, Karamana, during 2019-2020 in randomized block design with eleven cropping systems [rice-fallow-fallow (T1), rice-rice-fallow (T2), rice-dhaincha – cowpea (T3), (rice + dhaincha)- rice – green gram (T4), rice – cassava – amaranthus (T5), ricecassava- cowpea (T6), rice – para grass- fodder cowpea (T7), rice- fodder cowpea – fodder maize (T8), rice- bhindi – culinary melon (T9), rice – bhindi – yard long bean (T10) and rice – rice – amaranthus (T11)], each replicated thrice. In treatment T4, dhaincha was used for brown manuring. It was raised as an intercrop by sowing seeds @ 20 kg ha,-1 two days after transplanting rice and was later incorporated by spraying 2, 4- D @ 1.0 kg ha -1 at 50 per cent flowering stage (45 DAS). The varieties used were, Uma (rice), dhaincha local (dhaincha), Anaswara (cowpea), CO-8 (green gram), Vellayani Hraswa (cassava), Arun (amaranthus), local (paragrass), CO-8 (fodder cowpea), African Tall (fodder maize), Salkeerthi (bhindi), KAU Vishal (culinary melon) and Vellayani Jyothika (yard long bean). During virippu, the highest yield of rice was in T9 (5016 kg ha-1) and the lowest in T1 (3463 kg ha-1). Fodder cowpea produced the highest yield among the crops grown during mundakan (24434 kg ha-1) and summer (26620 kg ha-1). The rice equivalent yield (REY) in mundakan and summer seasons differed significantly among the systems. The REY in mundakan was the highest in T10 (16761 kg ha-1) which was on par with T9 (16419 kg ha-1). The least REY in mundakan was obtained from T3 and T7 (486 kg ha-1). The highest REY in summer was obtained from T10 (7348 kg ha-1) followed by T11 (6532 kg ha-1) which were on par. Rice - bhindi - yard long bean sequence (T10) produced the lowest weed dry matter at 20 DAS (46.95 g m-2) and 40 DAS (33.15 g m-2). Highest weed dry matter at 20 DAS (75.80 g m-2) and 40 DAS (87.32g m-2) was recorded in T1 at the end of the crop cycle. Treatment T10 had the highest weed smothering efficiency (WSE) at 20 DAS (38.07 %) and 40 DAS (63.20%) at the end of the crop cycle. Data on influence of physical properties of soil at the end of crop cycle among the cropping systems revealed that, the greatest decrease (8.09%) in bulk density over the initial value was observed in T9 while T1 showed an increase in bulk density (1.37%). The highest increase in water holding capacity was observed in T4 (8.59%) while T1 showed a decrease in water holding capacity by 7.43% over the initial value by the end of the crop cycle. Soil pH did not vary significantly among the cropping sequences. Significantly higher organic C (1.94%, 1.86%), labile C (2310 mg kg-1, 1614 mg kg-1) and water-soluble C (33.69 mg kg-1 , 21.70 mg kg-1) at 0-15 cm and 15-30 cm respectively were recorded in T9 at the end of the crop cycle. Results on available nutrient status in soil at the end of crop cycle revealed that, the highest available nitrogen was noticed in T10 (342.87 kg ha -1) while available P and K did not show any significant variation among the cropping systems. Exchangeable Ca was the highest in T5 (215.08 mg kg-1) while exchangeable Mg and available Fe did not show any significant variation among the cropping systems. Available Zn was the highest in T6 (3.697 mg kg-1). At the end of crop cycle, T10 (rice - bhindi - yard long bean), T5 (rice - cassava- amaranthus) and T6 (rice- cassava – cowpea) recorded the highest urease (91.07 mg g- 1 h-1), acid phosphatase (31.16 μg g-1 h-1) and dehydrogenase activity (34.51, μg g-1 h-1) respectively. Perusal of data on total nutrient uptake by crops at the end of crop cycle divulged that among the cropping systems, the highest N uptake (234.70 kg ha-1) was in T8 while highest P (54.92 kg ha -1) and K uptake (244.90 kg ha-1) were noticed in T6. T5 recorded highest Ca (114.20 kg ha -1) and Fe uptake (12.60 kg ha-1) while T3 and T7 recorded highest Mg (81.89 kg ha -1) and Zn uptake (17.62 kg ha-1) respectively. Total nutrients recycled through crop residues at the end of crop cycle showed that, T4 recorded the highest nitrogen recycled (19.52 kg ha -1) while T6 recorded the highest P recycled (5.13 kg ha -1) and T10 recorded the highest K (17.04 kg ha -1) recycled. Highest Ca (8.61 kg ha -1) and Zn (1.55 kg ha -1) were recycled by T9 while T7 recorded the highest Mg recycled (8.16 kg ha -1) and T3 (1.81 kg ha -1) recorded the highest Fe recycled. Data on total nutrients removed by weeds by the end of crop cycle revealed that T7 recorded the least N removal (18.07 kg ha -1) while T8 recorded lowest P removal (6.70 kg ha -1) and T10 recorded lowest K (19.85 kg ha -1), Mg (2.24 kg ha -1) and Zn removal (0.015 kg ha -1). T8 recorded the lowest Ca removal (0.72 kg ha -1) and T3 recorded the lowest Fe removal (0.077 kg ha -1). The removal of all nutrients assessed was highest in T1. Results from CO2 emission study revealed that in mundakan, T5 (281 ppm) and T6 (283 ppm), with cassava exhibited lower CO2 emissions. T5 (25.93 ºC) recorded the least and T4 recorded the highest (32.24 ºC) soil temperatures in mundakan season. T7 and T8 recorded significantly higher soil temperatures (37.80 ºC) and the least (34.03 ºC) was noticed in T1 in summer season. The highest soil moisture was recorded in T4 (23.43%) which was on par with most of the treatments and the lowest value of soil moisture was noticed in T1 (15.92%) during mundakan. The highest rice equivalent yield (28.93 t ha-1), maximum gross returns (₹ 9,01,865 ha-1) and net returns (₹ 5,45,705 ha-1) were obtained in T10 (rice - bhindi - yard long bean). The B:C ratio was the highest for T9 (rice – bhindi - culinary melon) (2.64) followed by T10 (rice - bhindi - yard long bean) (2.53). Based on data of three years, the highest stability index was recorded in rice –cassava – cowpea (T6) (0.95) while rice - bhindi - yard long bean (T10) sequence had the lowest (0.42). The second experiment revealed that rice crop following rice – cassava – amaranthus (T5) was superior in terms of number of grains per panicle (113), grain yield (3934 kg ha-1) and straw yield (4311.67 kg ha -1). Significantly higher weed dry weight was recorded in T1 (48.25 g m-2) and the lowest in T5 (9.86 g m-2) at 20 DAS. At 40 DAT, significantly higher weed dry weight was noticed in T1 (96.12 g m-2) while the lowest was in T4 (23.66 g m-2). The treatment T8 recorded the highest weed smothering efficiency (80%) which was on par with T5 (79.63%) and T4 (77.05%) at 20 DAT. At 40 DAT, T4 recorded significantly higher weed smothering efficiency (74.33%). Significantly highest NUE was in the treatment T5 (8.62) and the lowest in T1 (5.74). Available NUE was highest in T5 (9.72) followed by T6 (9.24) which were on par, while T1 (7.06) showed lowest value of available NUE. It could be concluded that, among different rice based cropping systems in lowlands, rice – bhindi – yard long bean (T10) performed better in terms of yield, economics, weed dynamics and soil health. Cropping systems with cassava during the mundakan season had lower CO2 emissions. Rice crop succeeding rice – cassava – amaranthus (T5) was superior in terms of number of grains per panicle (113), grain yield (3934 kg ha -1) and straw yield (4311 kg ha -1), NUE (8.61) and available NUE (9.72).