Balanced and integrated use of organic and inorganic fertilizers may enhance the accumulation of soil organic matter and improves soil physical properties. A field experiment having randomized complete block design with four replications was conducted for 36 years at Punjab Agricultural University (PAU), Ludhiana, India to assess the effects of inorganic fertilizers and farmyard manure (FYM) on soil organic carbon (SOC), soil physical properties and crop yields in a maize (Zea mays)–wheat (Triticum aestivum) rotation. Soil fertility management treatments included were non-treated control, 100% N, 50% NPK, 100% NP, 100% NPK, 150% NPK, 100% NPK + Zn, 100% NPK + W, 100% NPK (-S) and 100% NPK + FYM. Soil pH, bulk density (BD), electrical conductivity (EC), cation exchange capacity, aggregate mean weight diameter (MWD) and infiltration were measured 36 years after the initiation of experiment. Cumulative infiltration, infiltration rate and aggregate MWD were greater with integrated use of FYM along with 100% NPK compared to non-treated control. No significant differences were obtained among fertilizer treatments for BD and EC. The SOC pool was the lowest in control at 7.3 Mg ha⁻¹ and increased to 11.6 Mg ha⁻¹ with 100%NPK+FYM. Improved soil physical conditions and increase in SOC resulted in higher maize and wheat yields. Infiltration rate, aggregate MWD and crop yields were positively correlated with SOC. Continuous cropping and integrated use of organic and inorganic fertilizers increased soil C sequestration and crop yields. Balanced application of NPK fertilizers with FYM was best option for higher crop yields in maize–wheat rotation.

Precision nitrogen (N) management sustains high grain yield with low N optimum dose and thus may help reduce the escape of reactive nitrogen from soils to the atmosphere. Two-year field studies were conducted at two locations in sub-tropical and sub-humid climate in Indo-Gangetic plains of South Asia with the objectives to establish precision N management technology for fertilizer N topdressings in spring maize while quantifying nitrous oxide emission from soil. A significant positive correlation of 0.64 to 0.90 between LCC (Leaf color chart) scores and leaf N concentrations at different growth stages indicated that LCC scores can successfully be used as an index of leaf N content for precision N management in spring maize. A close linear relationship (R² = 0.75) between chlorophyll meter (SPAD) readings and LCC score showed that like SPAD meter, LCC score can reliably consider leaf greenness as an indicator of leaf N concentration. Cate-Nelson plot of LCC scores verses relative grain yield expressed LCC score 5 as the threshold for sustaining potential yield. Fertilizer N topdressings based on threshold leaf greenness of LCC 5 produced 6 to 10 percent higher grain yield with improved recovery and agronomic efficiencies in comparison to soil-test based N recommendations. Nitrous oxide emission estimated using Cool Farm Tool (CFT); an empirical model specified that application of 120 kg N ha⁻¹ at LCC 5 down turned nitrous oxide emission by 8.0 percent compared to soil test-based N management.

Transformations of applied phosphorus (P) fertilizer to inaccessible residual soil P is the main cause of inadequate P availability to plants in the majority of the cultivated soils. This study investigated the effect of organic wastes (rice-residue biochar, farmyard manure (FYM), poultry manure (PM), green manure (GM), and wheat straw (WS) on residual-P mobilization and its bioavailability in maize crops under different P status soils. Surface soil samples of ‘medium-P’ (12.5–22.5 kg P ha⁻¹) and ‘high-P’ (22.5–50.0 kg P ha⁻¹) status soils were collected from a long-term differential P fertilization experiment on maize-wheat rotation and were subjected to examine P adsorption/desorption, phosphatase activity and microbial biomass P (MBP) after incubation with organic amendments of varying elemental composition. The incorporation of organic manures decreases P sorption with maximum decrease in FYM-treated soils, indicating increased P concentration in soil solution. In contrast, WS due to its wider C/P ratio increased P sorption and did not produce any significant impact on the bioavailability of P. High-P status soils witnessed lower P sorption than medium-P soils. The MBP increased in the order of PM > FYM > GM > WS > biochar irrespective of soil P status. The availability and mobility of residual-P with FYM and PM was significantly higher than that of residual-P from biochar, GM and WS. Organics with wider C/P ratio immobilize bioavailable P in the short term regardless of soil P status.

Site-specific fertilizer nitrogen (N) management using chlorophyll meter (SPAD meter) can help drawing in-season need-based N topdressing decisions. However, SPAD meter based threshold chlorophyll value to trigger supplement N in spring maize is indistinct. Field studies were conducted for two years in sub-tropical and sub-humid climate to study variations in spectral properties and to establish threshold SPAD value for need-based N management in spring maize cultivars. Results specified that N concentration of topmost fully expanded leaf was closely correlated with SPAD meter readings from six-leaf stage (V6) to tasseling stages (VT). The Cate-Nelson plot expressed SPAD 50 as the threshold value to determine plant N need at different growth stages. Need-based topdressings of 30 kg N ha⁻¹, whenever SPAD reading fell below the threshold 50 improved grain yield production by 7.6 to 10.2 per cent over soil test-based N application. SPAD threshold 45 guided N management was inadequate to meet plant N demand, whereas SPAD threshold 55 guided N application lead to N doses in excess of crop requirement without yield benefits. SPAD threshold 50 guided N management ensured better demand-supply synchrony throughout the growth stages and thus reported better N recovery and agronomic efficiencies over soil test-based N management.

Ensuring food security and simultaneously maintaining environmental integrity has become a major challenge in modern agriculture. Quantification of trade-offs between productivity, fertilizer use and greenhouse gas (GHG) emissions in agriculture is important for the development of management strategies to ensure food security and environmental sustainability. The present study investigated the effect of synthetic fertilizer (SF) versus SF plus farmyard manure (FYM) in various combinations on soil fertility, grain yield and agronomic efficiency (AE) and GHG intensity (GHGI) in spring-maize for four years. A combination of 100% of the recommended NPK along with FYM (100%NPK+FYM) resulted in maximum (20–24%) increase in soil organic C content over 100%NPK alone treatment. Similarly, 100%NPK+FYM increased soil available N, P and K by 20, 73 and 33% over 100%NPK treatment. Continuous use of integrated nutrient management (INM) practices had a favourable impact on spring-maize grain yield, maximum being in 100%NPK+FYM (8.09 t ha⁻¹) and 125%NPK+FYM (8.16 t ha⁻¹) treatments. Though the grain yield between 100%NPK+FYM and 125%NPK+FYM treatments was similar, maximum AE of N, P and K and minimal GHGI was achieved in 100%NPK+FYM treatment. The results of the study indicated that application of 100%NPK+FYM in spring-maize proved to be agricultural and environmental sustainable management practice.