Optimizing Soil Moisture and PAR Utilization with Fertilizer Splitting for Rainfed Rice (Oryza sativa L.)
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Date
2021
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Department of Soil Science & Agricultural Chemistry, BAU, Sabour
Abstract
The present investigation entitled “Optimizing Soil Moisture and PAR Utilization with Fertilizer Splitting for Rainfed Rice (Oryza sativa L.)” was carried out during the kharif seasons of 2017 and 2018 on a sandy loam soil of Bihar Agricultural College farm, Sabour to derive inputs for rationalizing the use of K and N fertilizers by splitting and real time management respectively for making them more suitable for rainfed conditions. Nutrient and water management are important for diversifying and intensifying the rainfed rice based cropping systems. The experiment involved three K splitting schemes viz., K0(No K application), K40 (K applied as basal @ 40 kg K2O per ha) and K20+20 (K application as basal, and at panicle initiation stage @ 20 kg K2O per ha)in main plots, and five N splitting schemes in sub plots viz.,N0 (No N application), N50+50 (N application as basal and at active tillering, each @ 50 kg per ha) NSPAD (N application as basal each application @ 33.33 kg ha-1 and top dressing as guided by SPAD meter with critical SPAD value of 38, NGS (N application as basal @ 33.3 kg per ha and top dressing as guided by Green Seeker optical sensor) and N33+33+33 (N application as basal, at active tillering and at panicle initiation, each @ 33.3 kg per ha.).
The recommended fixed time split N applications under rainfed conditions are not adequate to synchronize N supply with actual N demand due to variations in crop N demand. During 2017, NSPAD resulted in an additional N application of 33 kg ha-1 in 5 out of 9 cases. However during 2018 no plot under NSPAD received any extra N application. This could have possibly resulted because of greater uniformity among various plots due to cultivation of lentil crop in the preceding rabi season.
It was generally observed that N- application time through 1st topdressing increased beyond active tillering stage by up to one week. However, the 2nd top dressing was still achieved by panicle initiation stage. Under rainfed conditions, real time N management can promote crop growth. Real time N management as in NSPAD and NGS resulted in reduced tiller mortality during the reproductive stage. Reduced tiller mortality is suggestive of optimized soil moisture and radiation utilization under real time N management. K application in two split doses stimulated tillering in rice crop. The tillers were significantly higher by 5.24 and 7.28 per cent with K application in two split doses over single basal application and no K application respectively and decreased the death of tillers during the reproductive stage of the crop. K application in two split doses also significantly increased the number of effective tillers by 5.30 and 7.64 per cent over single basal application and no K application respectively. This again suggests that split application of K results in better utilization of intercepted radiation and acquired water and nutrients by rainfed rice. NSPAD recorded significantly higher value of growth and yield attributes as compared to other N splitting schemes during both the years. NSPAD recorded significantly higher grain yield (3941 kg ha-1) in comparison to other N-splitting schemes. At active tillering stage the available nitrogen content in the 0-15 cm depth of soil was significantly lower in N0 in comparison to other N splitting schemes. Restricting nitrogen availability in the surface soil could be a potential tool under rainfed conditions to stimulate deeper root penetration in rice to tap subsurface water and nutrients. The increase in N uptake in NSPAD over fixed time N splitting regimes has proved that the rice crop requires lower N at the early stages, more N during its grand growth period (panicle initiation to flowering) and a comparatively lower N during the later stages of crop growth. Thus NSPAD promotes sufficient nitrogen application for increased nutrient uptake and yield in rainfed rice. K application in two split doses under rainfed conditions reduces the stress tolerance as compared to single basal application and no K application. Precise dose and real time N management as in NSPAD resulted in reduced stress tolerance indices. GreenSeeker optical sensor guided fertilizer N application at AT and PI stage in rainfed rice can lead to improved nitrogen use efficiency because of lower N fertilizer application rates than in fixed time N application. Under rainfed conditions, higher initial application of nitrogen as in N50+50 or in NSPAD resulted in greater photo synthetically active radiation interception in comparison to NGS and N33+33+33 during the early vegetative stage. However, towards the early reproductive stage, PAR interception in N50+50 became significantly lower than in N33+33+33, NSPAD and NGS. This again indicates that maintaining greater temporally staggered nutrient availability provides benefits in terms of PAR interception and utilization.
Thus, it can be concluded that SPAD based N application is the best treatment in terms of growth, yield and nutrient uptake on account of N fertilizer splitting in rainfed conditions. This assumes greater significant considering that despite the uncertainty in soil moisture regime of the rainfed rice crop; optical sensor measurement can help in better management of fertilizer nitrogen.