Fertilizer-N application and straw incorporation impacts crop productivity due to changes in total organic carbon (TOC), its labile pools and the soil enzymatic activity. A field experiment was established (in 2010) to study the effect of fertilizer-N application (0, 90, 120, and 150 kg N ha⁻¹) and rice straw (RS) incorporation (0, 5.0, 7.5, and 10 Mg ha⁻¹) on crop yield, C input, TOC and its labile pools and soil enzymatic activity under rice (Oryza sativa L.)—wheat (Triticum aestivum L.) cropping system (RWCS) in north-western India. Data showed that fertilizer-N application and RS incorporation significantly (p < 0.05) increased the rice and wheat grain yield, compared with control (CK). However, the RS incorporation alone did not impact crop yields. The sustainable yield index (SYI) for wheat was significantly lower with RS incorporation alone as compared with the other treatments. For rice, SYI was significantly higher for RS_7.5N₁₂₀, and was non-significant compared with the RS_10.0N₁₂₀. Annual total C input in soil plow layer (0–15 cm) under RWCS varied between 3.34 and 9.78 Mg C ha⁻¹, which was higher by 4.4 Mg C ha⁻¹ yr⁻¹ (~2.3-times) in RS_10.0, compared with CK. The conjoint application of fertilizer-N and RS incorporation (RS_10.0N₁₅₀) significantly increased the TOC, water extractable organic C (WEOC), hot water C (HWC), microbial biomass C (MBC) and basal soil respiration (BSR) due to increased soil enzymatic activity viz. dehydrogenase activity (DHA), fluorescein diacetate (FDA) and alkaline phosphatise (Alk-P). A significant increase in potassium permanganate oxidizable C (KMnO₄-C) with RS incorporation under RS_10.0N₁₅₀ increased the C management index (CMI), and hence the soil quality. The inter-correlations between highly weighted soil variables among different principle components (PCs) revealed that KMnO₄-C in PC₁, FDA activity in PC₂, and BSR in PC₃ with the highest correlation were the sensitive indicators for assessing soil quality in a RWCS.

Soil and crop management practices affect soil processes, agro-ecosystem functioning and sustainability of agricultural production systems. Organic farming production system is being promoted as a low cost environment friendly production system for, improved human and soil health, better environment, and increased agricultural sustainability. The reviewed literature is in consensus that organic farming, undoubtedly, improves soil quality due to application of organic manures and composts, and adoption of legume-based diversified cropping systems. Conversely, there is also consensus on lower productivity of crops (5–58%) under organic farming than the conventional system though exceptions are there. Despite the lower crop productivity, it may become more profitable if price premiums are available on organic produce. Its role in improving nutritional quality of produce though is debatable; but owing to absence of synthetic inputs organic produce is generally considered to be safer and healthy. The organic farming practices are expected to improve the soil quality over imbalanced and discriminate use of agro-chemical inputs. In sole productivity terms, organic farming may not be a viable farming system but in terms of overall ecosystem services, the system definitely has an edge over the conventional system.

Soil carbon (C) pools and biological indicator plays an important role in maintaining soil quality. Land use change from naturally undisturbed to intense cultivation had significant impact on C storage due to change in soil biological properties. The present study was conducted to understand the impact of land use change from the uncultivated to intensively cultivated soils under rice–wheat and cotton–wheat cropping system on labile and stable C pools, soil microbial and enzymatic activity, and a change in nutrient availability. The Olsen’s P concentration was significantly (p < 0.05) higher in soils under rice–wheat, while ammonium acetate (NH₄OAc)-K was higher in the uncultivated soils, compared with others. Soils under cotton–wheat cropping system had significantly lower total organic carbon (TOC) in contrast to rice–wheat soils. The uncultivated soils had the highest TOC concentration, which was ∼20.2% higher than rice–wheat and ∼46.4% than the cotton–wheat soils. The water extractable organic carbon (WEOC) was the smallest organic C fraction (∼0.31%–0.40% of TOC), and was significantly lower in cotton–wheat soils. The basal soil respiration (BSR) and mineralization quotient (qM) were significantly higher for rice–wheat, compared with the cotton–wheat soils. These microbial indices were improved due to increased alkaline phosphates (Alk-P) and dehydrogenase (DHA) enzymatic activity in soil. Soil microbial biomass C (MBC) was significantly higher (by ∼31.7%–57.3%) in the uncultivated than the cultivated soils which has increased the C mineralization in soil. The stable C pool comprised ∼68.8% of TOC in the uncultivated soils, almost similar to rice–wheat soils (∼68.5%), but higher than cotton–wheat soils (∼61.9%). The stable C pool leads to C rehabilitation indicated by higher C management index for rice–wheat soils. The principal component analysis (PCA) distinct the uncultivated soils from the cultivated soils under two cropping systems based on BSR and labile C (Fract. 2) in PC₁ (explaining ∼82.7% of total variability), and the microbial (qmic) and mineralization (qM) quotient in PC₂ (∼17.3% variability). These indicators were most influential for studying C dynamics of the natural ecosystem and restoring the cropland ecosystem by suitable soil management practices.

Intensive tillage, removal or burning of crop residues, limited organic manure use, declining irrigation water resources and scarcity of labour are the major causes of soil degradation and unsustainability of rice (Oryza sativa L.)–wheat (Triticum aestivum L.) system (RWS) in South Asia.Resource conservation technologies (RCTs) such as zero tillage (ZT), dry direct seeded rice (DSR) and crop residues retained as mulch have shown promise to increase the productivity and profitability of RWS in South Asia. Effects of RCTs on soil biological parameters are unclear and contradictory. We evaluated the effects of conservation agriculture practices on changes in soil biochemical properties at different growth stages of wheat grown as the fifth crop in RWS. Twelve treatment combinations of tillage, crop establishment and crop residue management included four main plot treatments in rice: (1) conventional tillage (CT)-DSR,(2) ZT-DSR, (3) DTR, ZT machine transplanted rice and (4) PTR, conventional puddled transplanted rice. The three subplot treatments were: (i) CTW-R, CT wheat with both rice and wheat residues removed, (ii) ZTW-R, ZT wheat with residues of both the crops removed and (iii) ZTW+R, ZT wheat with rice residue retained as surface mulch in subsequent wheat. Irrespective of rice establishment methods, mean wheat grain yield under ZTW+R was 6% and 10% greater than CTW-R and ZTW-R respectively. Soil enzyme activities increased (5–18%) under ZTW+R compared with ZTW-R and CTW-R at different growth stages of wheat. The residual effect of rice establishment methods was significant on soil enzyme activities during wheat cropping, which were highest under ZT-DSR followed by CT-DSR, DTR and PTR. Soil organic carbon content in the 0–7.5 cm layer was significantly higher (7–9%) under the ZTW+R treatment compared with all the other treatments. Principal component analysis (PCA) identified three enzyme activities (dehydrogenase, fluorescein diacetate and phosphatase), and soil organic carbon content as the most sensitive indicators for assessing soil quality for RWS based on conservation agriculture. The PCA discriminated rice establishment systems with rice residue as surface mulch from rice establishment systems without rice residue and the maximum tillering stage from the other stages of wheat. The present study provided reliable biochemical indicators to monitor soil biological quality changes in response to conservation agriculture practices in RWS.