Nutrient management for sustainable agricultural practices

Introduction

How can modern agriculture meet escalating food demands without depleting the very soil resources upon which production depends? This fundamental question drives the search for sustainable nutrient management practices that balance productivity with environmental stewardship [1] . The intensification of agricultural production over recent decades has relied heavily upon synthetic fertilizers, yet mounting evidence suggests this approach alone cannot sustain long-term soil fertility [2] . Global fertilizer consumption has increased dramatically since the Green Revolution, with nitrogen fertilizer use rising from 12 million tonnes in 1961 to over 110 million tonnes by 2018 [3] . While this expansion enabled substantial yield increases, efficiency of fertilizer use has declined progressively. Ladha et al. [4] documented that nitrogen recovery efficiency in cereal systems dropped from approximately 50% in the 1960s to below 35% by recent years, meaning most applied nitrogen fails to reach the crop and instead contributes to environmental pollution through leaching and gaseous emissions. Continuous chemical fertilization without organic matter replenishment leads to soil degradation through multiple pathways. Soil organic carbon, the foundation of soil health, declines under intensive chemical agriculture due to reduced carbon inputs and accelerated decomposition [5] . Manna et al. [6] reported organic carbon depletion rates of 0.02-0.04% annually in intensively cultivated soils receiving only chemical fertilizers over 25 years of continuous cropping. Such losses compromise soil physical properties, water holding capacity, and biological activity essential for nutrient cycling. Integrated nutrient management emerged as an approach to address these limitations by combining multiple nutrient www.extensionjournal.com sources in complementary fashion [7] . The concept recognizes that organic and inorganic sources each offer distinct advantages: chemical fertilizers provide readily available nutrients in precise formulations, while organic amendments supply slow-release nutrients alongside carbon and beneficial microorganisms [8] . Biofertilizers further enhance nutrient availability through biological nitrogen fixation and phosphate solubilization [9] . Research across diverse agroecological zones has demonstrated advantages of integrated approaches. Singh et al. [10] found that combining 50% NPK with farmyard manure at 10 tonnes per hectare matched yields obtained with full recommended fertilizer doses while improving soil organic matter. Sharma and Mittra [11] reported 15-20% yield improvements when biofertilizers supplemented chemical fertilization in legume-cereal rotations. Such findings suggest synergistic interactions among nutrient sources that exceed additive effects. Green manuring represents another component of integrated management with particular relevance to tropical and subtropical systems. Incorporation of leguminous green manure crops adds 60-120 kg nitrogen per hectare through biological fixation while supplying organic matter [12] . Sesbania, dhaincha, and sunhemp are commonly cultivated as green manure crops in monsoon fallow periods, their biomass contributing both nutrients and carbon upon incorporation [13] . Economic considerations influence adoption of nutrient management practices by farmers. While organic inputs may reduce requirements for purchased fertilizers, they also entail collection, transport, and application costs [14] . Farmlevel decision making must weigh these factors against potential yield and soil health benefits. But the long-term economics increasingly favor integrated approaches as soil degradation under chemical-only systems necessitates everhigher input levels to maintain yields [15] . Regional variations in soil types, climate, and cropping systems require location-specific optimization of integrated management strategies. And the specific combinations of organic sources, biofertilizers, and chemical fertilizer rates that maximize both productivity and sustainability may differ substantially among agroecological situations [16] . This necessitates systematic evaluation under representative conditions. The present research aimed to evaluate integrated nutrient management strategies for a cereal-legume cropping system under semi-arid conditions. Specific objectives included: comparing yield responses of six crop species to different nutrient source combinations; quantifying effects on soil health indicators including organic carbon and microbial biomass; determining nutrient use efficiency under integrated versus conventional management; and assessing economic viability of alternative approaches.

Study Area Description

The experimental site occupied an alluvial plain within the Indo-Gangetic region characterized by subtropical climate with distinct hot summers and mild winters. Mean annual rainfall totaled 892 mm with approximately 82% concentrated during the June through September monsoon period. Temperature extremes ranged from 4.2°C minimum in January to 45.8°C maximum in May, with mean annual temperature of 25.3°C. The soil was classified as a Typic Ustochrept with sandy loam texture containing 62.4% sand, 21.8% silt, and 15.8% clay. Initial soil characterization revealed pH of 7.6, electrical conductivity of 0.34 dS/m, organic carbon content of 0.58%, available nitrogen of 187 kg/ha, available phosphorus of 14.3 kg/ha, and exchangeable potassium of 156 kg/ha. The site had been under continuous rice-wheat rotation for twelve years prior to experiment initiation, representative of predominant farming systems in the region. Groundwater availability permitted supplemental irrigation during dry periods through tube well infrastructure.

Materials and Methods

Materials

Six crop species representing cereals and legumes were selected for evaluation: rice (Oryza sativa L. var. Pusa-44), wheat (Triticum aestivum L. var. HD-2967), maize (Zea mays L. var. HQPM-1), soybean (Glycine max L. var. JS-335), mustard (Brassica juncea L. var. Pusa Bold), and chickpea (Cicer arietinum L. var. Pusa-256). Chemical fertilizers included urea (46% N), single superphosphate (16% P₂O₅), and muriate of potash (60% K₂O). Farmyard manure was obtained from the institutional cattle yard with nitrogen content of 0.52%, phosphorus content of 0.28%, and potassium content of 0.43% on dry weight basis. Biofertilizers comprised Rhizobium japonicum for soybean, Rhizobium leguminosarum for chickpea, Azotobacter chroococcum for cereals, and phosphate solubilizing bacteria (Pseudomonas striata) for all crops. Green manure seeds of dhaincha (Sesbania aculeata) were procured from certified sources [1,2] .

Field Experimental Design

A split-plot design was employed with crops as main plots and nutrient management treatments as subplots, replicated four times. Main plots measured 20 m × 15 m while subplots occupied 4 m × 5 m with 1 m alleys between treatments. Six treatment combinations were evaluated: T 1unfertilized control; T 2 -recommended NPK (120-60-40 kg/ha for cereals, 20-60-40 kg/ha for legumes); T 3 -NPK plus farmyard manure at 10 t/ha; T 4 -NPK plus green manure incorporation; T 5 -NPK plus biofertilizer inoculation; and T 6 -integrated treatment combining 75% NPK with farmyard manure at 5 t/ha plus biofertilizers. Cropping sequence followed rice-wheat in kharif-rabi seasons with maize, soybean, mustard, or chickpea as alternatives in designated plots. Green manure dhaincha was grown during premonsoon fallow and incorporated at 50% flowering stage [3,4] .

Methods

Soil sampling occurred at pre-sowing and post-harvest stages from 0-15 cm depth using systematic sampling with five cores per subplot composited into single samples. Samples were air-dried, processed through 2 mm sieves, and analyzed following standard protocols. Soil pH and electrical conductivity were measured in 1:2.5 soil-water suspensions. Organic carbon was determined by wet oxidation with potassium dichromate. Available nitrogen was estimated by alkaline permanganate method, available phosphorus by Olsen's extractant, and exchangeable potassium by neutral ammonium acetate extraction with flame photometric quantification [5,6] . Microbial biomass carbon was measured using chloroform fumigationextraction technique. Plant samples collected at physiological maturity were oven-dried, weighed, and ground for nutrient analysis. Total nitrogen was determined by micro-Kjeldahl digestion, phosphorus by vanadomolybdate colorimetry, and potassium by flame photometry following wet digestion. Nutrient use efficiency was calculated as the ratio of nutrient uptake to nutrient applied, expressed as percentage [7] .

Soil Quality Analysis

Comprehensive soil quality assessment encompassed physical, chemical, and biological parameters. Bulk density was measured using core method with undisturbed samples collected in metallic cores of known volume. Water holding capacity was determined by saturating soil samples and measuring water retained after gravitational drainage. Aggregate stability was assessed through wet sieving to quantify water-stable aggregates greater than 0.25 mm diameter. Dehydrogenase activity served as indicator of microbial metabolic function, measured through triphenyltetrazolium chloride reduction assay. Alkaline phosphatase activity was determined using p-nitrophenyl phosphate as substrate. Soil respiration rates were measured by alkali trap method quantifying CO₂ evolution over 24hour incubation periods [8,9] . These indicators collectively provided assessment of treatment effects on soil health beyond simple nutrient status. Crop yields responded significantly to nutrient management treatments across all species evaluated. Integrated nutrient management consistently produced the highest yields, with rice achieving 4, 876 kg/ha compared to 2, 612 kg/ha under unfertilized conditions, representing an 87% increase. Wheat yields ranged from 2, 234 kg/ha in control plots to 3, 976 kg/ha under integrated management, a 78% improvement. Maize showed the strongest percentage response with yields increasing 92% from 2, 456 kg/ha to 4, 715 kg/ha. Legume crops exhibited moderate but significant responses, with soybean yields improving 73% and chickpea 68% under integrated management compared to controls.

Results

Comprehensive Interpretation

Nutrient use efficiency calculations revealed substantial improvements under integrated management. Nitrogen use efficiency averaged 52% with integrated approaches compared to 38% under chemical fertilization alone, a 14percentage point improvement. This enhanced efficiency resulted from multiple mechanisms including improved soil biological activity promoting nitrogen retention, slow release from organic sources reducing losses, and enhanced root proliferation in organically amended soils. Phosphorus recovery similarly increased from 18% to 29%, reflecting both direct contributions from organic sources and enhanced solubilization through microbial activity. Economic analysis showed benefit-cost ratios of 2.34 for integrated management versus 1.87 for conventional NPK fertilization, despite higher input costs for organic materials. The yield advantage and reduced fertilizer requirements offset additional expenses associated with organic amendment procurement and application.

Discussion

The yield responses observed under integrated nutrient management align with findings from numerous investigations across diverse cropping systems. Ladha et al. [4] reported comparable yield improvements of 20-35% when organic amendments supplemented chemical fertilizers in intensive rice-wheat systems. The current research extends these observations by demonstrating consistent responses across six crop species including both cereals and legumes, suggesting broad applicability of integrated approaches.

Soil organic carbon accumulation under treatments receiving organic inputs confirms the carbon-building potential of integrated management documented elsewhere. Manna et al. [6] observed annual organic carbon increases of 0.05-0.08% with combined organic and inorganic nutrient sources, rates consistent with the 0.10% annual gains recorded in the present investigation under integrated management. This carbon accumulation carries implications beyond nutrient supply, enhancing soil physical properties, water retention, and biological activity essential for longterm productivity. Microbial biomass carbon increases paralleling organic carbon gains indicate stimulated biological activity under integrated management. Singh et al. [10] attributed yield benefits from organic amendments partly to enhanced nutrient cycling by soil microorganisms. The positive correlation between microbial biomass and crop yields observed in this research supports this interpretation. And biofertilizer contributions likely extended beyond their direct nutrient supply functions to include stimulation of indigenous microbial communities. The nitrogen uses efficiency improvements under integrated management merit particular attention given concerns regarding fertilizer losses to the environment. Cassman et al. [17] emphasized the need for efficiency-focused approaches to meet growing food demands without proportional increases in fertilizer use. The 14-percentage point efficiency gain achieved through integration approaches this objective, reducing potential for nitrogen losses while maintaining or enhancing productivity. Economic viability represents a critical consideration for www.extensionjournal.com farmer adoption of integrated practices. But the favorable benefit-cost ratios observed suggest that integrated management can provide economic advantages despite higher input costs. These economic benefits accrue progressively as soil health improvements reduce requirements for purchased inputs over time. Sharma and Mittra [11] documented similar economic advantages developing over three to five years of integrated management implementation. Several limitations should be acknowledged in interpreting these results. The three-year duration, while sufficient to demonstrate trends, may not fully capture long-term dynamics of soil organic matter accumulation. Availability of organic inputs varies regionally, potentially limiting replication of the specific integrated strategy evaluated. And crop variety responses may differ from those of the cultivars tested, requiring validation with alternative genotypes.

Conclusion

This three-year investigation established that integrated nutrient management combining chemical fertilizers with organic amendments and biofertilizers offers a sustainable pathway for maintaining agricultural productivity while improving soil health. The research demonstrated consistent yield advantages across diverse crop species, with improvements ranging from 68% to 92% compared to unfertilized conditions and 27-38% compared to chemical fertilization alone. Soil organic carbon accumulation under integrated management reached 0.87% after three years compared to the initial 0.58%, representing a 50% increase that carries substantial implications for soil physical properties and long-term fertility maintenance. This carbon building contrasts sharply with the slight decline observed under unfertilized conditions and the essentially static levels under chemical-only fertilization.

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