SUMMARY: Knowledge of different fractions and availability of boron (B) is essential while studying the response of crops to B. Fractionation provides information about the chemistry of B and quantifies its bioavailability. Such information is potentially valuable for predicting bioavailability, B leaching, dynamics, transformation between chemical forms in soils and environmental impacts. Total B (T-B) is quantified into five fractions: readily soluble (Rs-B), specifically adsorbed (Spa-B), oxide bound (Ox-B), organically bound (Org-B) and residual B (Res-B). Of these, Rs-B is the fraction present in soil solution and adsorbed weakly by soil particles, and is most readily available for plant uptake. It accounts for 1–2% of T-B. The second most plant available form is Spa-B; it may be adsorbed onto clay surfaces or associated with organic matter (OM) in soil. The remaining fractions, Ox-B, Org-B and Res-B, are unavailable for plant uptake. The major portion (generally 87·4–99·7%) of T-B is composed of Res-B. Overall, the relative proportion of B in various fractions is in the order of Res B > Org-B > Spa-B > Rs-B > Ox-B. Several factors such as soil pH, soil OM, clay minerals, iron and aluminium oxides and calcium carbonate content may change the relative proportion of B in various fractions and the transformations among different soil B fractions. Some of the B fractions are correlated with others and exhibit responses in terms of plant growth. Non-specifically adsorbed (Nsa-B) and Spa-B are positively and significantly correlated to some sub-fractions of Ox-B, such as B occluded in manganese oxyhydroxides (Moh-B). The most readily available forms of B for plants are Nsa-B, Spa-B and Moh-B.

Land-use changes (LUC), primarily due to deforestation and soil disturbance, are one of the major causes of soil quality degradation and greenhouse gas emissions. Effects of LUC on soil physicochemical properties and changes in soil quality and land use management strategies that can effectively restore soil carbon and microbial biomass levels have been reported from all over the world, but the impact analysis of such practices in the Indian context is limited. In this study, over 1,786 paired datasets (for meta-analysis) on land uses (LUs) were collected from Indian literature (1990–2019) to determine the magnitude of the influence of LUC on soil carbon, microbial biomass, and other physical and chemical properties at three soil depths. Meta-analysis results showed that grasslands (36.1%) lost the most soil organic carbon (SOC) compared to native forest lands, followed by plantation lands (35.5%), cultivated lands (31.1%), barren lands (27.3%), and horticulture lands (11.5%). Our findings also revealed that, when compared to forest land, the microbial quotient was lower in other LUs. Due to the depletion of SOC stock, carbon dioxide equivalent (CO₂ eq) emissions were significantly higher in all LUs than in forest land. Results also showed that due to the conversion of forest land to cultivated land, total carbon, labile carbon, non-labile carbon, microbial biomass carbon, and SOC stocks were lost by 21%, 25%, 32%, 26%, and 41.2%, respectively. Changes in soil carbon pools and properties were more pronounced in surface (0–15 cm) soils than in subsurface soils (15–30 cm and 30–45 cm). Restoration of the SOC stocks from different LUs ranged from a minimum of 2% (grasslands) to a maximum of 48% (plantation lands). Overall, this study showed that soil carbon pools decreased as LUC transitioned from native forestland to other LUs, and it is suggested that adopting crop-production systems that can reduce CO₂ emissions from the intensive LUs such as the ones evaluated here could contribute to improvements in soil quality and mitigation of climate change impacts, particularly under Indian agro-climatic conditions.

Cereal crop production gains under conventional agricultural systems in India have been declining in recent years because of inadequate management practices, creating a considerable concern. These activities were shown to deplete soil organic matter stocks, resulting in a decrease in microbial activity and soil organic carbon (SOC) content. Moreover, even with minimal use of organic sources in cultivated land, soil carbon status deteriorated, particularly in subtropical climates. Integrated nutrient management (INM), a modified farming method, has the potential to effectively utilize organic and inorganic resources, to improve the quality of soils and crops, and making farming more economically viable and sustainable. The aim of this study was to use meta-analysis to quantify the effects of INM on crop production, soil carbon, and microbial activity in Indian soils. During the years 1989–2018, data from various research studies in India, mainly on nutrient management in rice and wheat crops, were collected. Meta-Win 2.1 software was used to analyze the results, and significance was determined atp< 0.05. The results showed that the yield of rice and wheat was 1.4 and 4.9% more in INM than that in 100% NPK (N: nitrogen, P: phosphorous, and K: potassium), and that respective yields were comparatively higher in loamy soils (2.8%) and clayey soils (1.0%). The INM treatment increased SOC and microbial biomass carbon (MBC), resulting in improved overall soil quality. The SOC stock was increased by 23.8% in rice, 15.1% in wheat, 25.3% in loamy soils, and 14.4% in clayey soils in INM over 100% NPK. Microbial quotient (MQ) data showed significant trends between different management systems in both soil types, for example, INM > 100% NPK > No NPK. Due to more soil cracking and reduced aggregate stability in the rice field (greater short-term soil structural changes), the SOC stock loss in rice was higher than that in wheat. The CO₂equivalent emissions were 7.9 Mg ha⁻¹higher in no NPK (control) than in 100% NPK, and 16.4 Mg ha⁻¹higher in control than in INM. In other words, INM increased soil carbon sequestration by 2.3 Mg ha⁻¹as compared to using 100% NPK. Overall, the findings of this study show that INM could be a viable farming system mode in India for improving crop production, increasing soil carbon sequestration, and improving microbial activity while remaining economically and environmentally sustainable.

Agroforestry systems (AFSs) have potential to combat climate change and to ensure food security. AFSs can sequester carbon and amend the organic matter, thereby enhancing the crop productivity. Carbon sequestration depends on the type of AFSs, climate, cropping pattern, and management practices. The aim of this study was to evaluate different AFSs for their potential to sequester carbon and impact on soil organic matter (SOM) in the eastern sub-Himalayas, India. Hedge-, alder-, and guava-based AFSs were established along with control (without any tree), and the maize–mustard–potato cropping pattern was followed in each AFS. Soil samples were collected after the fifth crop cycle and further analyzed. The results showed that crop productivity was significantly higher in all the AFSs than control. On average, soil organic carbon (SOC) was found to be significantly higher by 62 and 64% in hedge-based AFSs as compared to guava-based AFSs and control, respectively, andat parwith alder-based AFSs. Particulate organic carbon (POC) was higher in all the three AFSs than in the control. For microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) contents, the trend of AFSs was expressed as alder-based AFS > hedge-based AFS > guava-based AFS > control. Hedge- and alder-based AFSs had higher SOC stocks than guava-based AFSs and control. Carbon dioxide equivalent (CO₂eq.) emissions were greater in control than hedge-based AFSs (35.2 Mg ha⁻¹), followed by alder-based AFSs (28.6 Mg ha⁻¹), and the lowest was observed in guava-based AFSs. On an average, hedge species accumulated more nitrogen (N), phosphorus (P), and potassium (K), which were 60, 12, and 28 kg ha⁻¹yr⁻¹, respectively. This conclusively proved that AFSs were significantly affecting SOM pools and crop productivity and had a significant role in carbon retention in the soil. Overall, hedge- and alder-based AFSs retained higher soil carbon, and hence, hedge- and alder-based AFSs may be promoted to achieve climate-smart agriculture practices in the acid soils of the Indian sub-Himalayan region.

A field experiment was conducted to investigate the influence of long-term application of organic manures on aggregate stability, associated carbon concentrations and carbon pools as an important soil-quality parameter under a scented rice-potato-onion cropping system in silt-loam textured soil in Eastern Bihar, India (subtropical climatic condition). Five treatments were used: 1) nitrogen, phosphorus and potassium (NPK) – 100% recommended dose of NPK; 2) NPK+FYM (farmyard manure) – 50%NPK+50% N as FYM; 3) FYM+VC (vermicompost)+ NC (neem cake) – different organic sources each equivalent to 1/3 of the recommended N (FYM +VC +NC); 4) FYM+VC+NC+PSB (phosphate-solubilizing bacteria – different organic sources each equivalent to 1/3 of the recommended N (FYM +VC+NC)+biofertilizers containing N and P carriers (PSB) and 5) FYM+BFN+BM+PSB – 50% N as FYM + biofertilizer for N +Bone meal to substitute P requirement of crops + PSB. The aggregate size distribution (>250 μm) at different soil depths is higher in treatment FYM+VC+NC+PSB and is at par with FYM+VC+NC, followed by FYM+BFN+BM+PSB and NPK+FYM, and the lowest in treatment receiving 100% NPK. The mean carbon concentration in each soil fraction was higher in soil depth 0–10 cm, followed by 10–20 cm and 20–30 cm. The trend of mean weight diameter (MWD) in different treatments was FYM+VC+NC+PSB ≥ FYM+VC+NC > NPK+FYM > FYM+BFN+BM+PSB > NPK. The trend of carbon concentrations in different treatments was FYM+VC+NC+PSB ≥ FYM+VC+NC > FYM+BFN+BM+PSB ≥ NPK+FYM > NPK. Non-labile pool of carbon forms the major portion (60.14%) of the total soil organic carbon (SOC) irrespective of all depths. Bulk density (BD) has a significant role in stabilizing soil aggregates as well as increasing the SOC content in soil. SOC was negatively correlated with BD (r = −0.870, p = 0.05), MWD (r = −0.911, p = 0.01) and geometric mean diameter (GMD) (r = −0.958, p = 0.05) irrespective of depth. This study took further steps toward understanding the enhancing of aggregate stability on organic manures addition for soil quality improvement.

Due to the introduction of zero-till wheat in the Indo-Gangetic plains (IGP) in India, irrigation and fertilizer nitrogen (N) management needs to be modified from that followed under conventionally tilled fields. A field experiment was conducted to study the effect of irrigation and N levels on yield and N uptake by zero-till wheat, fertilizer N-use efficiency, and distribution of nitrate-N (NO₃-N) in a soil profile under zero-till conditions in an acidic alluvial soil of the eastern IGP. The experiment was laid out in a split-plot design with four levels of irrigation as main plots (I₀-no irrigation, rain-fed, I₁-122 mm in one irrigation at 21 days after sowing (DAS), I₂-263 mm in two irrigations at 21 and 42 DAS, and I₃-386 mm in three irrigations at 21, 42, and 84 DAS) and 4 N levels [0 (N₀), 60 (N₁), 120 (N₂), and 150 (N₃) kg N ha⁻¹] as subplots. Grain and straw yields were significantly higher at the irrigation level-I₂ and 120 kg N ha⁻¹-N₂ over the control (I₀ and N₀) and were at par with the highest applied levels of irrigation and N (I₃ and N₃). The nitrogen uptake by wheat followed a trend similar to yield for irrigation levels; however, it increased significantly up to 150 kg N ha⁻¹. After the harvest of wheat crop, more NO₃-N was observed in the 60–90 cm subsurface soil layer than in the surface 0–15 cm and/or 15–30 cm and 30–60 cm subsurface soil layers. The highest NO₃-N concentration was recorded in the treatment I₂N₂. Accumulation of NO₃-N in the soil increased up to irrigation levels I₂ and with increasing doses of fertilizer N application. Combined applications of irrigation and N had a positive and significant influence on agronomic efficiency (AE) and apparent N recovery (ANR) but had no significant effect on physiological efficiency (PE). This study suggests that an appropriate combination of irrigation and N levels in zero-till wheat can lead to not only high-yield levels and N-use efficiency but also adequately control NO₃-N leaching under acidic alluvial soils in the eastern IGP.