Effect of green manuring with dhaincha (Sesbania aculeata) on growth and yield of direct-sown and transplanted rice under intermediate deepwater conditions (0–50 cm)

SUMMARYIn intermediate deepwater conditions (0–50 cm) at Cuttack, India during 1990 and 1991, rice and dhaincha (Sesbania aculeata) were either mixed-sown in different arrangements (parallel lines and mixed broadcasting) in dry soil by the end of May or rice seedlings were transplanted in plots grown with pure dhaincha after the accumulation of water in the field by mid-July. Incorporation of dhaincha in situ after 48 and 54 days of growth added 60·8–65·2 and 72·9–76·9 kg N/ha in the mixed stands compared with 81·3 and 85·1 kg N/ha in the pure stand in 1990 and 1991 respectively. Although the growth of rice when sown simultaneously with dhaincha was affected initially due to the more vigorous growth and shading by the latter, tillering of rice increased after the incorporation of green manure following an increase in inter-row spacings. The performance of the direct-sown and transplanted rice was similar in 1990, when the water level rose relatively slowly, but in 1991 the transplanted crop yielded significantly less due to the sudden accumulation of water to higher depths (48 cm), resulting in greater mortality of seedlings at planting. However, the grain yield of both directsown and transplanted crops increased with dhaincha green manuring compared with the control (no application of dhaincha) and was equal to the application of 40 kg N/ha applied as urea fertilizer. The highest yield was obtained when rice and dhaincha were grown at a 2:1 ratio in 20 cm wide rows and the clonal tillers uprooted from the adjoining rice rows were planted in lines vacated by dhaincha. The yield was, however, equal to that from treatments where rice and dhaincha were grown in alternate rows at 15 cm spacing or mixed broadcasting. Increase in yield under green manuring was due to greater panicle weight, which was probably due to a continued supply of N following decomposition of organic matter added through dhaincha. Therefore, green manuring of direct-sown rice with dhaincha was beneficial for higher crop productivity under excess water conditions.

Effect of seed rate and row spacing on the performance of early and late maturing rice cultivars in mixed crop systems under intermediate deepwater conditions (15–50 cm)

SUMMARYA field experiment was conducted in 1990 and 1991 under intermediate deepwater conditions (15–50 cm) at Cuttack, India with two rice cultivars - Banaprabha, a semi-tall (130 cm), short duration (95 days), upland cultivar and Gayatri, a photosensitive, semi-dwarf (100 cm), lowland cultivar of long duration (170 days). The cultivars were direct-sown either in pure stands using 400 seeds/m2 at 20 cm row spacing or in mixed stands composed of alternate rows sown with 200, 300 or 400 seeds/m2 each at 10, 15 or 20 cm inter-row spacing. Mixed-row cropping of Banaprabha and Gayatri produced 17–21% higher grain yield than a pure crop of Gayatri. Panicles/m2 increased with higher seed rate and decreased with wider row spacing but a reverse trend was observed in panicle weight. Maximum grain yield was obtained at a row spacing of 15 cm but the effect of varying seed rates at each row spacing was non-significant. Gayatri produced up to 82% of its pure crop yield and contributed up to 70% of the total yield in the mixed crop system. Therefore, the yield advantage under mixed cropping was due to the late maturing cultivar benefitting from the increased area available after the harvest of the early cultivar. A crop stand using 200–300 seeds/m2 of each cultivar at a 15 cm row spacing was found to achieve the optimum productivity from the mixed cropping system.

Effect of varying seed rates and transplanting clonal tillers on the performance of rice under intermediate deepwater conditions (0–80 cm)

SUMMARYUnder intermediate deepwater conditions (0–80 cm) at Cuttack, India, direct sowing of the semi-tall rice variety Utkalprabha with 200–800 seeds/m2 produced similar yields in 1989 when heavy rainfall (105 mm) after sowing resulted in more than 50% germination, followed by the gradual accumulation of water in the field. However, in 1990, which was characterized by drought in the initial stages, leading to poor germination (35–40%), followed by a sudden accumulation of water, the crops sown at 200 seeds/m2 produced a significantly lower grain yield than those sown at higher seed rates. Higher seed rates increased plant height, tillers/m2 and panicles/m2 but the associated decrease in panicle weight resulted in similar grain yield production. There was no decrease in the yield of crops sown at all seed rates in 1989 and at > 400 seeds/m2 in 1990 when clonal tillers were removed after 60 days to transplant either the equivalent of or double the uprooted plot area. The loss due to decrease in panicles/m2 with the removal of clonal tillers was compensated for by the resulting increase in panicle weight. The crop planted from clonal tillers produced a significantly higher grain yield than that planted from seedlings of equivalent age raised in a nursery seed-bed with or without fertilizer application. Furthermore, the clonal-propagated crop tolerated simulated flash-flooding better at the early vegetative stage, measured by less tiller mortality and relatively higher dry matter production than in the crop raised from nursery seedlings. Therefore, planting with clonal tillers uprooted from a well-established direct-sown crop is recommended under excess water conditions.

Optimum sowing date and nitrogen fertilizer rate for rice varieties under intermediate deepwater conditions (15–50 cm)

SUMMARYIn an intermediate deepwater situation (15–50 cm) at Cuttack, India, three improved high-yielding rice varieties, Utkalprabha (semi-tall), CR 292–8051 (intermediate tall) and Gayatri (semi-dwarf) were sown on 20 May, 30 May and 10 June in 1988 and 1989 with an application of either 0, 20 or 40 kg N/ha at sowing. Tall varieties performed better than the dwarf type but grain yield decreased with delay in sowing. The early-sown crops (20–30 May) germinated with pre-monsoon rains and were established well before water accumulated in the field from mid-June onwards. The late-sown crops (10 June), despite good initial germination, could not withstand immediate waterlogging. The tall variety, Utkalprabha, elongated faster with rising water level and escaped complete submergence; whereas the semi-dwarf Gayatri failed to withstand such extreme excess water stress. Application of N fertilizer up to 40 kg/ha proved beneficial to the crops sown by the end of May. However, with crops sown on 10 June, the application of N could not compensate for the loss in yield due to an inadequate initial crop stand. Therefore, early sowing of tall varieties by the end of May along with a basal application of N fertilizer is recommended for higher productivity of rice under excess water conditions.

Flood tolerance of rice grown under intermediate deepwater conditions (15–50 cm) as affected by phosphorus fertilization

SUMMARYThe effect of phosphorus fertilizer on the performance of an improved semi-dwarf (100 cm), long duration (170 days), photosensitive rice variety CR 1016, grown under conditions of intermediate deepwater (15–50 cm) and simulated flash flooding (80 cm), was investigated at Cuttack, India in 1985, 1987 and 1988. Growth and yield of rice subjected to overhead flash flooding (complete submergence) at the vegetative stage for 10 days was decreased significantly compared with partial submergence in water of intermediate depth. The adverse effect of complete submergence was due to greater tiller mortality and lower number and/or weight of panicles at maturity. Rice plants fertilized with P tolerated flooding better and produced significantly higher grain yields than when no P was applied. There was no significant effect of P application on the crop grown under natural unsubmerged conditions, except when it was raised in the same plots as the previous year and may therefore have benefited from residual effects. Therefore, application of 8.7–17.5 kg P/ha along with 60 kg N and 16.7 kg K/ha at sowing was essential to overcome the deleterious effects of submergence on rice grown under waterlogged conditions.

Effect of Mixed Row Cropping of Early and Late Maturing Rice Varieties on Crop Productivity under Intermediate Deepwater Conditions

SUMMARYTwo early maturing semi-tall (120–130 cm) rice varieties, Kalinga-3 (85 days duration) and Banaprabha (95 days duration), were compared in pure and mixed crop stands under intermediate deepwater conditions (15–50 cm) with a modern late maturing (170 days duration) semi-dwarf (100 cm) variety, CR 1016. Parallel line seeding of CR 1016 and Kalinga-3 or Banaprabha in alternate rows (1:1 ratio) 20 cm apart yielded 19% more grain than a pure crop of CR 1016 alone. Mixed crop planting in a 1:2 or 2:1 ratio or with reduced inter-rovv spacing gave no additional yield advantage. Mixed row cropping prevented lodging in early varieties, whereas monocrops of the same varieties were partially lodged and showed some premature seed germination. The better and more stable yields obtained from such mixed cropping could be beneficial to resource poor farmers growing rice in conditions of excess water.

Effect of form, method and time of urea nitrogen application on growth, yield and nitrogen uptake of direct sown and transplanted rice under intermediate deep water (15–50 cm) conditions

SummaryUnder intermediate deepwater (15–50 cm) conditions, sulphur-coated urea (SOU) drilled behind the plough at sowing was superior to other coated (neem, lac, coaltar) urea materials and broadcast incorporation of prilled urea in increasing the yield of direct-sown rice. In transplanted rice, the grain yield was highest with urea super granules (USG) placed 30 days after transplanting (DAT) followed by SOU broadcast incorporation at planting. N-use efficiency increased considerably with SCU drilled behind the plough or USG placed 20 days after sowing in shallow standing water in direct-sown rice and SCU broadcast incorporation or USG placed 30 DAT in transplanted rice.

Effect of methods of stand establishment on grain yield of rice under intermediate deep water conditions (15–50 cm)

SummaryIn intermediate deepwater conditions (15–50 cm), direct seeding was superior to transplanting in 20 cm of water. Varieties with greater plant height performed better under transplanted conditions. Nitrogen fertilizer application at 40 kg/ha increased the grain yield under both direct-seeded and transplanted conditions. Though yield of the transplanted crop was less than that of the direct-seeded crop, the decrease was less in the crop given nitrogen fertilizer.

Comparative efficiency of different planting methods in intermediate deepwater (15–50 cm) rice

SummaryIn rainfed lowland rice areas of intermediate deepwater (15–50 cm), transplanting in greater depths of water (50–60 cm) with clonal tillers (double transplanting) from 20 or 40- to 50-day-old-transplanted crops of similar environment increased grain yield significantly compared with seedlings of the same age (60 or 80- to 90-day-old) from a nursery. The grain yield did not decrease significantly when the clonal tillers were removed at 20 or 40 days after transplanting compared with that of the undisturbed crop. The practice of double transplanting (clonal propagation) increased tiller production and the number of panicles, and the crop could tolerate better the greater depths of water and thereby give greater grain yield.