PhD

The study entitled “Bridging productivity loss in aerobic rice (Oryza sativa L.) through land configuration and intercropping” was undertaken at College of Agriculture, Vellayani, during 2018 – 2022. The main objectives were to compare the performance of rice varieties under contrasting water regimes, to assess the effect of land configuration and intercropping on weed dynamics, yield and productivity of aerobic rice and to work out the economics.
The study was conducted as two separate experiments at IFSRS, Karamana. The experiment I on the effect of water regimes and biofertilizer on rooting pattern of rice was carried out from February to June 2021, using PVC pipe method. There were 18 treatment combinations, replicated four times. Three rice varieties viz., v1-Prathyasa (MO 21), v2-KAU Manu Rathna (HS 16) and v3-Sharada (MAS 946-1) were raised under three different water regimes, w1- conventional/flooded (5 cm water column throughout the crop growth), w2 - saturated condition (irrigating to 1 cm depth one day after the disappearance of standing water column) and w3 - aerobic condition (irrigation to 2.5 cm depth and subsequent irrigation once in five days), with (a1) and without (a0) Azospirillum lipoferum (KAU isolate).
Experiment II was conducted to study the effect of land configuration and intercropping in aerobic rice, during March to June 2020 and February to June 2021. This study was conducted in two separate layouts corresponding to the land configurations – flat bed (FB) and saturated soil culture - raised bed (SSC-RB) systems. This experiment comprised intercropping aerobic rice (var. Prathyasa) with three pulses, viz., p1-cowpea (var. Kanakamony), p2-green gram (var. CO 8) and p3-black gram (var. DU 1), in 1:1 (r1) and 2:1 (r2) row proportions. The experiment was laid out in randomized block design with six treatment combinations and four replications. The treatment combinations were p1r1 – aerobic rice + cowpea in 1:1, p1r2 – aerobic rice + cowpea in 2:1, p2r1 – aerobic rice + green gram in 1:1, p2r2 – aerobic rice + green gram in 2:1, p3r1 – aerobic rice + black gram in 1:1 and p3r2 – aerobic rice + black gram in 2:1. Sole crops of rice, cowpea, green gram and black gram were raised in both the land configurations for computing intercropping indices.
The results of experiment I revealed significantly higher rooting depth (RD), root dry weight (RDW), root volume (RV) and root : shoot in the variety, Sharada (v3) and under aerobic condition (w3). A. lipoferum (a1) also enhanced these rooting traits. Among the interactions, the highest RD was recorded in v3w3 (43.41 cm), v3a1 (35.94 cm), w3a1 (35.52 cm) and v3w3a1 (46.41 cm) while v3w3 recorded higher RDW (9.15 g per plant).
Physiological parameters viz., root oxidizing activity (ROA), relative leaf water content (RWC), proline, total soluble protein (TSP), membrane stability index (MSI), chlorophyll stability index (CSI) and water productivity (WP) were significantly higher in Sharada (v3) whereas stomatal frequency (SF), stomatal conductance (SC) and transpiration rate (TR) were higher in KAU Manu Rathna (v2) and least in Sharada. Phenomenal increase was observed in proline content and ROA under aerobic condition (1.31 µmol g-1 FW and 89.34 µg g-1 FW h-1, respectively). Similarly, aerobic condition (w3) resulted in the highest water productivity (0.74 kg m-3) followed by saturated (0.56 kg m-3) and flooded condition (0.42 kg m-3). Flooded condition (w1) recorded significantly higher chlorophyll content (2.47 mg g-1 FW), nitrate reductase activity (443.13 µg g-1 FW) and CSI (83.43 %) and was comparable with saturated condition (w¬2). Significantly higher RWC, TSP, SF, SC, TR and MSI were observed under flooded condition (w1). Among the interactions, v3w3 recorded the highest proline content (1.53 µmol g-1 FW) while the highest SF was recorded in v2w1 (71.83 nos mm-2) and v2w2 (68.83 nos mm-2). Sharada recorded the least SF under all the three water regimes, ranging from 54.00 to 57.17 nos mm-2.
The variety, Sharada (v3) recorded the tallest plants, leaf area index (LAI), dry matter production (DMP), filled grains per panicle, 1000 grain weight and the least sterility percentage. Aerobic condition significantly reduced the growth and yield attributes over flooded condition. Grain yield was significantly higher in Sharada (311 g m-2) followed by Prathyasa (287 g m-2) which was on par with KAU Manu Rathna (278 g m-2). Among the water regimes, flooded condition resulted in the highest grain yield (324 g m-2) followed by saturated (283 g m-2) and it was on par with aerobic condition (269 g m-2).
The results of experiment II, revealed that intercropping with cowpea (CP) and green gram (GG) resulted in significantly taller plants of aerobic rice at maximum tillering (MT) and panicle initiation (PI) stages under both SSC-RB and FB. Intercropping with CP and GG also increased the LAI of aerobic rice at all the stages under SSC-RB. Except relative growth rate (RGR), the mean growth attributes of aerobic rice was considerably higher under SSC-RB.
Significantly more number of filled grains per panicle and lower sterility percentage were recorded in aerobic under intercropping with CP and GG, in both SSC-RB and FB systems. The pooled analysis revealed that intercropping aerobic rice with pulses in 2:1 ratio recorded significantly higher grain yield in aerobic rice under SSC-RB (1.85 t ha-1) and FB (1.42 t ha-1). Similarly, the straw yield of aerobic rice was significantly higher in 2:1 row proportion under both the configurations, during both the years. The SSC-RB system recorded significantly higher number of productive tillers m-2 (460.82, 486.27), number of filled grains per panicle (108.47, 112.37), thousand grain weight (24.58 g, 25.43 g), grain yield (1.64 t ha-1, 1.50 t ha-1), and lower sterility percentage (16.01 %, 11.08 %) of aerobic rice, during the first year and second year.
Intercropping with CP and black gram (BG) recorded significantly higher RWC under FB, chlorophyll content under SSC-RB and higher SC and MSI under both SSC-RB and FB systems in aerobic rice. Proline accumulation was remarkably higher when intercropped with GG and BG under both the land configurations. The mean chlorophyll content and SC of aerobic rice were significantly higher under SSC-RB (2.80 mg g-1 FW and 0.52 mol m-2 s-1, respectively) while the proline content was higher under FB (1.19 µmol g-1 FW) over SSC-RB (0.71 µmol g-1 FW). This could be attributed to the higher soil moisture content under SSC-RB as compared to FB system. On an average, the soil moisture content at 20 days interval was 23.68 per cent under SSC-RB and 16.83 per cent under FB systems.
Among the intercropped pulses, GG recorded significantly taller plants and higher DMP at 30 DAS, both under SSC-RB and FB systems. However, at the harvest stage, BG and CP proved to be taller with higher DMP. Cowpea recorded considerably more number of primary branches per plant, root nodules, RD and RV. Black gram and GG produced more number of pods per plant under SSC-RB and FB systems, as compared to CP. Cowpea (p1) recorded the highest hundred seed weight and seed : pod under SSC-RB and FB. The seed : pod of BG was comparable with that of CP. The pooled analysis revealed that CP recorded the highest seed yield (993 kg ha-1, 731 kg ha-1) followed by BG (871 kg ha-1, 629 kg ha-1) and GG (652 kg ha-1, 461 kg ha-1) under SSC-RB and FB, respectively. The row proportion of 1:1 resulted in higher seed yield of pulses (905 kg ha-1, 675 kg ha-1) than 2:1 row proportion. Cowpea (p1) and BG (p3) recorded the highest harvest index under both SSC-RB and FB systems. The SSC-RB system recorded significantly higher mean number of pods per plant (42.14, 40.12), seed yield (826 kg ha-1, 852 kg ha-1) and haulm yield (2,159 kg ha-1, 2,157 kg ha-1).
Land equivalent ratio (LER) values were higher for p3r2 (1.48), both under SSC-RB and FB. Aggressivity (A) and competition ratio (CR) were positive for pulses in all the intercropping systems, except in p2r1 under FB during the first year indicating dominance of pulses. The highest A value was observed under p3r2 (+0.828) and p1r2 (+0.696). Relative crowding coefficient (RCC) was higher in p3r2 (12.32) and p2r2 (10.43), while CR was higher in p3r2 (1.81), and p1r2 (1.65) followed by p2r2 (1.44). Competition index (CI) values were lower under p3r2 (0.049), p2r2 (0.053) and p1r2 (0.059). Percentage yield difference (PYD) was the highest (48.39 %) for intercropping with BG in 2:1 proportion (p3r2). Rice equivalent yield (REY) was higher when aerobic rice was intercropped either with BG or CP in 1:1 or 2:1 row proportions. The mean aggressivity and CR were significantly higher under SSC-RB over FB during the second year. The mean REY was remarkably higher under SSC-RB (4,122 kg ha-1, 4,044 kg ha-1) over FB (3,168 kg ha-1, 2,954 kg ha-1) during the first and second year, respectively.
Significantly lower weed density (WD) and weed dry weight (WDW) were recorded in aerobic rice + CP intercropping with the highest weed smothering efficiency, both in SSC-RB and FB systems, during both the years. The mean WD at 20 DAS and 40 DAS and WDW at 20 DAS, 40 DAS and 60 DAS were significantly higher in FB than in the SSC-RB system.
Intercropping with CP recorded the highest total uptake of nitrogen, phosphorus and potassium under both the land configurations. The 2:1 ratio resulted in higher total phosphorus and potassium uptake while 1:1 ratio recorded higher soil organic carbon (SOC) in SSC-RB. The total nitrogen, phosphorus, potassium, electrical conductivity and SOC were higher in SSC-RB.
Gross return, net return, benefit cost ratio (B:C), monetary advantage index (MAI) and monetary equivalent ratio (MER) indicated that BG and CP were remunerative at 1:1 and 2:1 proportions, than GG. The mean gross return (₹ 1,23,666 ha-1 and ₹ 1,21,326 ha-1), net return (₹ 55,375 ha-1 and ₹ 53,035 ha-1), B:C (1.82, 1.77) and MAI (₹ 31,713 ha-1 and ₹ 26,015 ha-1) were significantly higher under SSC-RB than FB, during the first and second year, respectively.
From the study it could be concluded that the variety, Sharada performed better under different water regimes even in the absence of A. lipoferum. Compared to Sharada, the yield reduction of Prathyasa and KAU Manu Rathna were to the tune of 8.36 per cent and 11.87 per cent respectively over the contrasting water regimes. Rooting traits were positively influenced by A. lipoferum. Intercropping aerobic rice with either black gram or cowpea in 1:1 (p3r1, p1r1) or 2:1 (p3r2, p1r2) row proportions under SSC-RB system could be recommended for better weed control, higher productivity in terms of rice equivalent yield and economics of aerobic rice during the summer season.