P.V.N PRASADBOTHA PRASHANTHI2023-11-152023-11-152023-11-15D6380https://krishikosh.egranth.ac.in/handle/1/5810201200A field experiment entitled “Studies on impact of brown manuring in rice – maize sequence” was conducted for two consecutive years (2020-2021 and 2021-2022) on clay loam soils of the Agricultural College Farm, Bapatla. The experimental site was uniform in topography and homogeneously fertile. The soil pH was slightly alkaline in reaction, low in organic carbon, low in available nitrogen, medium in available phosphorus and high in available potassium status. The kharif experiment was laid out in a split plot design during both the years of rice crop. The main plot treatments consisted of brown manure species dhaincha (Sesbania aculeata) sown at three seed rates (20, 30 and 40 kg ha-1) and sub plot treatments comprising knockdown of dhaincha at four stages (20, 25, 30 and 35 DAS) using 2,4-D @ 0.5 kg ha-1 with three replications. During the succeeding rabi, the experiment was laid out on the same site in a split-split plot design to acommodate maize crop wherein, the three sub plot treatments imposed to kharif rice were divided into three sub-sub-plots to receive three nitrogen levels viz., control (no nitrogen), 75 % and 100 % RDN to each plot thus, making a total of 12x3=36 treatments during rabi. The cultivars used in the investigation were Samba mashuri (rice) and Pioneer P-3396 (maize) respectively. Among the three seed rates of dhaincha, the maximum biomass production, nitrogen and carbon input was recorded with seed rate @ 40 kg ha-1. With respect to timing of knockdown, the 35 days aged brown manure treatment registered the highest values. Dhaincha seed rate @ 40 kg ha-1 recorded significantly taller plants, higher leaf area index, number of tillers m-2, drymatter xxi accumulation and among the knockdown days maximum growth parameters were registered with BM at 30 days, which was found significantly superior to BM at 25, 35 and 20 days, while BM at 25 and BM at 35 days were comparable to each other. Number of panicles m-2, number of filled grains, grain yield, straw yield, NPK uptake, gross return, net return and B:C ratio were the highest with dhaincha seed rate @ 40 kg ha-1 and among the timing of knockdown of dhaincha the highest values were observed with treatment of brown manuring at 30 DAS. However, BM at 25 DAS maintained parity with BM at 35 DAS treatment. Non significant changes in test weight, harvest index, pH and EC of the soil either due to seed rates or timing of knockdown of dhaincha after harvest of rice were noticed. The highest organic carbon, microbial biomass carbon, residual available nitrogen, phosphorous and potassium were noticed with seed rate @ 40 kg ha-1 and among the sub plot treatments, knockdown at 35 DAS recorded the maximum organic carbon, which was however on par with BM at 30 DAS. Interaction effect of seed rates and timing of knockdown of dhaincha displayed significant behaviour with drymatter accrual at 90 DAS, number of panicles m-2 and grain yield of rice. Seed rate @ 40 kg ha-1 along with application of 2,4-D spray at 30 DAS registered the highest values followed by BM at 25 DAS at the same seed rate. Plant population was maintained at optimum level during both the years of study. The maximum plant height and drymatter accumulation of maize was recorded when the preceding rice was supplied with dhaincha seed rate @ 40 kg ha-1, While the seed rates @ 30 and 20 kg ha-1 depicted comparable behaviour with each other. The values of above parameters were significantly higher when knockdown of dhaincha was resorted at 35 DAS in preceding rice crop, which was however statistically comparable to brown manuring at 30 DAS. Application of 100% RDN was found to be the best treatment producing the highest growth attributes in maize. Days to 50 percent tasseling and silking of maize was not affected either by seed rates or timing of knockdown of dhaincha in kharif rice and nitrogen levels treatments to rabi maize. Number of cobs plant-1 was not significantly influenced by seed rate treatments of dhaincha in preceding rice crop. Among the sub plots, significantly higher number of cobs plant-1 was observed in BM at 35 DAS, however, it was on a par with BM at 30 and 25 DAS. With regard to nitrogen levels, the highest number of cobs plant-1 was observed with increased level of nitrogen i.e., 100% RDN. Significantly higher cob length, cob girth, number of grain rows cob-1 and number of grains row-1, grain yield cob-1, grain and stover yields of rabi maize were recorded when its preceding rice crop received the highest seed rate of dhaincha and conversely preceded seed rate @ 20 kg ha-1 of dhaincha in rice registered statistically lower values in maize, which was comparable to seed rate @ 30 kg ha-1. Among the sub plot treatments, brown manuring at 35 DAS followed by BM at 30 DAS registered higher values. Noticeably, the superior xxii values of above parameters and test weight were observed with the application of 100% RDN. Among the seed rates of dhaincha, preceding to maize, seed rate @ 40 kg ha-1 has registered the highest uptake of NPK by maize kernel and stover and reflected in agronomic use efficiency of succeeding maize, which was significantly superior to other treatments. Significantly higher NPK uptake and AUE was displayed with knockdown of dhaincha at 35 DAS in preceding crop and remained at par with BM at 30 DAS. A significant improvement of the above parameters in maize was observed with 100 % RDN. Physiological use efficiency and apparent nitrogen recovery of nitrogen of maize, pH and electrical conductivity of soil at harvest in maize failed to manifest any significant influence. The highest residual organic carbon, available N, P2O5, K2O of soil and economic returns of maize and the lowest values of these parameters were registered in 40 and 20 kg ha-1 seed rate of dhaincha treatment respectively and among the knockdown days BM at 35 DAS recorded higher values, which was however comparable to BM at 30 DAS. Significant difference in the organic carbon of soil was not observed with the various nitrogen levels applied to maize. Among the different levels of nitrogen, higher available N, P2O5 and K2O of the soil and monetary benefits were disclosed by the application of 100% RDN. The highest system productivity was observed with seed rate @ 40 kg ha-1 and it was significant over other seed rates. Among the timing of knockdown days, significantly the highest system productivity was recorded due to the brown manuring of dhaincha at 30 DAS imposed to kharif rice, which was statistically at par with 35 days age of knocking down of dhaincha. The higher dose of nitrogen @ 100% RDN in sub plots recorded higher system productivity during the two years of study and in pooled data and the lower values of system productivity were recorded with control plots.EnglishThesis