Soil health and nutrient fractions (P, K, and Zn) as influenced by long-term application of organics and inorganics in calcareous soil under rice-wheat cropping system
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Date
2021
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Dr.RPCAU, Pusa
Abstract
To examine the sustainability of any management practices long-term experiments are regarded as important tools. The long-term experiments could precisely evaluate the effect of continuous application of primary, secondary and micronutrients on overall soil health and crop productivity. Long-term fertiliser experiments could monitor the trends in crop yield resulting from changes in soil fertility. In India, several long-term studies have shown wide variability in crop productivity, and it is essential to monitor the long-term changes in crop yields, soil nutrient status, and nutrient supplying capacity to ensure and improve crop productivity. These considerations have prompted to undertake the present investigation, which was carried out in an on-going field experiment started in Rabi 1988-89 under AICRP on STCR project at Research Farm of Dr. Rajendra Prasad Central Agricultural University, Pusa, Samastipur, Bihar, India. The experiment was carried out with rice (Cv. Rajshree) and wheat (Cv. HD- 2733) as test crops for Kharif (2019) and Rabi (2019-20), respectively. The experimental site experienced a sub-tropical climate with an average annual precipitation of 1345 mm, the summer was hot and humid and too cold winter and the experimental soil belonged to order entisols. The experiment was conducted in a split-plot design with four levels of
fertilizers viz. no NPK (Fo), 50% of the recommended dose of NPK (F1), 100% of the recommended dose of NPK (F2) and 150% of the recommended dose of NPK (F3) were applied as treatments in main plots. The main plots were divided into four sub-plots in which treatments viz. no manures (M0), compost @ 10 t ha-1 (M1), crop residue (M2), and compost + crop residue (M3) were superimposed over NPK levels making a total of 16 treatment combinations with three replications. The study intended to assess the effect of the organic and inorganic treatments on soil health, nutrient fractions and crop performance in rice-wheat cropping system. Most of the observations were recorded thrice i.e., before transplanting of rice, after harvesting of rice and after wheat harvest.
The experimental findings of the effect of long-term application of organics and inorganics on soil physical properties revealed a significant reduction in bulk density up to the application of 150% NPK as inorganics, and a 15% decline was observed due to conjoint application of compost and crop residue over control (no organics). Soil penetration resistance reduced significantly due to the application of compost and organics down to a depth of 60 cm, and the maximum reduction (19%) over control (no organics) was observed with the conjoint application of compost and crop residue. Water holding capacity and volumetric moisture content increased significantly up to 150% NPK as inorganics, and conjoint application of compost and crop residue recorded the highest percent increase (27.5% and 12.5%, respectively) over control (no organics). Mean weight diameter of water-stable aggregates increased due to conjoint application of organics and inorganics and a recorded 1.5-fold increase over absolute control (no NPK, no organics). No significant changes were observed with soil pH and EC. Whereas, Soil organic carbon increased up to 1.7-fold over absolute control (4.44-4.91 g kg-1), up to 2-fold over 31 years of continuous application of organics and inorganics over control and was recorded highest (8.22-8.42 g kg-1) with the conjoint application of 150% NPK + compost + crop residue. Availability of N and P2O5 increased significantly up to 150% NPK, and with organics were recorded highest with the conjoint application of organics and inorganics. Due to the interaction effect between organics and inorganics, a 2-fold increase in the soil available N and a 4.5 fold increase in available P2O5 was observed with 150% NPK + compost + crop residue over absolute control (187.36-190.71 kg ha-1 and 13.71-15.25 kg ha-1, N and P2O5 respectively). Conjoint application with
organics performed better than the sole application of organics at all the three graded doses of NPK, i.e., 50%, 100% and 150%. No interaction effect was observed between organics and inorganics for available K2O content and responded up to 150% NPK and recorded highest with the conjoint application of compost and crop residue (144.12- 152.99 kg ha-1). After 31 years of continuous application of NPK, compost and crop residue available N, available P2O5 and available K2O were enhanced to a tune of 2-fold, 3.4-fold, and 1.6-fold, respectively, over control. Observations of soil biological properties revealed a 3-fold increase in soil microbial biomass carbon and nitrogen, a 2-fold increase in soil respiration and an 8-fold increase in soil dehydrogenase activity over absolute control due to the interaction effect of 150% NPK+ compost + crop residue. Also, 150% NPK+ compost + crop residue was 30% superior over absolute control for soil alkaline phosphatase activity. The distribution of different fractions of revealed that continuous application of organics and inorganics significantly affected all the fractions of P, and the highest total P was recorded with 150% NPK+ compost + crop residue. Among inorganic P fractions Ca10P and Ca8P (28% and 10%) contributed highest towards total P. Ca2P, and Ca8P increased by six times and 4.5 times, respectively over absolute control due to periodic application of 150%NPK + compost + crop residue. All the fractions of P were positively correlated with each other except for Ca10P. Among different forms of K, Structural K and non exchangeable K contributed highest (78% and 21%) towards total K. All the fractions of K increased due to increased application of inorganic fertilizers and organics, the treatments receiving 150% NPK and combined application of compost and crop residue recording the highest. Available K was highly correlated to non exchangeable and structural K. Most of the Zn in soil were present in form and was found as residual Zn (92% of total Zn). The highest rice yield (50 q ha-1) in terms of grain was observed with 150% NPK + compost + crop residue, and the same trend was followed with yields of wheat crop (46.11 q ha-1). Yield maximisation was observed with the conjoint application of compost and crop residue and inorganic fertilisers at all three doses as compared to the sole application of fertilisers. Nutrient uptake in terms of N, P, K and Zn followed the yield trend in both crops. Application of 100% NPK and 150% NPK performed equally in economic terms (B: C) though yield maximisation was observed with 150% NPK. Conjoint application of crop residue along with 150% NPK resulted in the best economics. This signifies the pronounced response of organics in calcareous soils.
Balanced application of organics and inorganic fertilisers provided a favourable environment for rice and wheat crops growth in the experimental calcareous soil. For yield maximization, farmers can be recommended with 100% recommended dose of NPK, but for sustainable crop production and soil health in calcareous soil, 150% NPK + compost + crop residue should be recommended. 100% crop residue returning along with 150% NPK could be most economical to enhance crop yield beyond the recommended dose of fertilisers.