Total Water Stable Aggregates Research Articles

Soil Aggregation and Aggregate-associated Carbon affected by Long-term Crop Residues Incorporation in Rice-Wheat Cropping System

Crop residue management is one of the options for enhancing soil organic carbon stabilization by improving soil aggregation in semi-tropical soil. We studied the influence of different levels crop residues incorporation on aggregation and carbon stabilization in different soil aggregates after 23 years of continuous rice- wheat cropping system on sandy loam calcareous soil. 100% residue incorporation caused a significant increment of 49.09 % in total water stable aggregates (>0.25 mm) in surface soil. Carbon content in both macro- and microaggregates was increased, but increment was greater in macroaggregates (33.47%) than microaggregates (16.23%). These results show that long-term application of organics in combination with inorganic fertilizers helped in carbon accumulation in macroaggregates, and thereby improving soil carbon status.

Impact of Long Term Nutrient Management on Soil Quality Indices in Rice-Wheat System of Lower Indo-Gangetic Plain

Globally, soil degradation is an important issue for sustainable crop production. Soil quality indicators are the soil attributes that address the ecological functions of soil. Therefore, indicator-based soil quality assessment has been emphasized for quantifying the relative soil quality changes in different nutrient management systems. Soil quality underthe rice (Oryza sativa L.) and wheat (Triticum aestivam L.) cropping system was assessed using a modified “Soil Management Assessment Framework (SMAF)” model. Soil’s physical, chemical, nutritional, and biological indices were analyzed for different nutrient management strategies, viz., inorganic fertilizer (NPK), NPK + 7.5 Mg ha−1 farmyard manure (NPKF), NPK + 10.0 Mg ha−1 paddy straw (NPKP) and NPK + 8.0 Mg ha−1 Sesbania sesban L. green manure (NPKG). Nutrient management strategies significantly influenced soil quality indices. NPKF showed the highest SMAF score for soil physical quality index followed by NPKP > NPKG > NPK and control; whereas the score of soil chemical quality was greater in NPKP followed by NPKF/NPKG > NPK > control (p > 0.05). Overall, the soil nutritional quality index was greater in NPKF (0.96) followed by NPKG > NPKP > NPK, and the least was in control. The SMAF score of soil biological quality index was highest in NPKF compared to NPKG > NPKP > NPK > control. The wholesome index of SMAF (SQI) was developed withthehighest score in NPKF (0.94) followed by NPKG (0.90) > NPKP (0.89) > NPK (0.79) > control (0.71). The β-glucosidase activity, mineralizable C, KMnO4 oxidizable N, microbial biomass C, and total water-stable aggregates explained 82% variability in the dataset and represented a good agreement with system yield (R2 = 0.89, p < 0.05). This study concludes that the conjunctive application of NPK with manures restores the overall soil quality more than other management practices, and thatthe SQ indices can be utilized for screening the best management practices for rice-wheat and other similar cropping systems.

Conservation agriculture influences crop yield, soil carbon content and nutrient availability in the rice–wheat system of north-west India

Context Tillage-based agriculture has led to soil health deterioration and decline in crop productivity. Recently, zero tillage (ZT) and crop residue management has emerged as an alternative to conventional tillage. Methods This experiment was done in north-west India over 3 years, with four treatments: (1) conventional transplanted puddle rice (TPR) + conventional tillage wheat (CTW) with 1/3 of wheat residues incorporated (TPR-CTWR1/3i); (2) TPR + CTW (TPR-CTW); (3) ZT direct-seeded rice (ZTDSR) + ZT wheat (ZTW) with 1/3 of wheat residues incorporated (ZTDSR-ZTWR1/3i); and (4) conventional tillage direct-seeded rice (CTDSR) + ZTW with full residues of both rice and wheat crop incorporated (CTDSR-ZTWRfr). Two rice (CSR 30, CSR 36) and two wheat (HD 2894, KRL 213) varieties were used. Soil samples were collected after harvest at 0–15 to 15–30 cm soil depth. Key results In rice, yield was significantly higher under conventional tillage, and variety CSR 36 outperformed CSR 30 in various yield attributes. In wheat, the number of grains per spike was significantly higher in TPR-CTWR1/3i than TPR-ZTW. After rice harvest, there was ∼10% and 5% higher available N in TPR-CTW and CTDSR-ZTWRfr compared to ZTDSR-ZTWR1/3i and TPR-CTWR1/3i, respectively (0–15 cm depth). After wheat harvest, highest SOC content (7.5 g kg−1) was found under CTDSR-ZTWRfr (0–15 cm depth); and highest total water-stable aggregates were observed under CTDSR-ZTWRfr (37.52%; 0–15 cm depth). Compared to farmers’ practise, the total global warming potential of rice–wheat cropping system was reduced by 43% with conservation agriculture-based management practises (ZTDSR-ZTWR1/3i). Conclusions DSR (in rice) and ZT in wheat with full residue retention best improved soil organic carbon and nutrient availability in soil. Implications Conservation agriculture systems can be adopted to improve crop productivity, soil health and reduce greenhouse gas emissions.

Evaluating the impact of midwestern cropping systems on soil health and soil carbon dynamics

Crop producers are becoming more interested in improving the health of their soils. The effects of cropping practices on soil health have been studied extensively, but much uncertainty remains. This study investigated the impacts of standard midwestern US agronomic practices on soil health indicators. The Soil Management Assessment Framework was used to quantify soil quality index (SQI) scores for each system. Corn–soybean (<i>Zea mays</i> L.–<i>Glycine max</i> L.) rotations received 168 kg N ha^–1 applied prior to corn. Treatments were the following: spring-applied urea ammonium nitrogen (SU168), fall-applied manure (FM) in no-till (NT) for 2 years (FM168NT2), FM with 10 years of NT and cereal rye (<i>Secale cereale</i>) cover crop (FM168NT10+R), and FM with 38 years of NT management (FM168NT38). Continuous corn (CC) treatments had FM applied annually at 224 kg N ha^–1 with eight years of stover removal (FM224CC-S) and with no stover removal (FM224CC). Soil cores were taken to a depth of 15 cm in the spring of 2017 and analyzed for total carbon (TC), total nitrogen (TN), water-stable aggregates (WSA), bulk density (BD), and potentially mineralizable nitrogen (PMN). Results showed that FM168NT38 and FM224CC had significantly greater TC and TN than other treatments. There were minimal treatment differences in total WSA &gt; 0.212 mm. No significant differences in PMN were found. Bulk density levels were significantly higher in NT treatments. The FM224CC and FM224CC-S treatments had the highest SQI scores, and FM168NT10+R had the lowest SQI score due to having higher BD and lower TC. Results suggest that the effect of cropping practices on some near-surface soil health indicators may be small and difficult to quantify. This study also demonstrated the need to adjust management to minimize compaction and maximize yield and soil health in cover-cropped systems. The study also monitored soil TC levels to a depth of 120 cm from 2007 through 2017. The rate of change in TC over time at a given depth did not differ between treatments. Total C levels did not change significantly to a depth of 15 cm. Significant increases in TC were found in all treatments except FM224CC-S at 30 to 60 cm and 90 to 120 cm depths, and in all treatments at 60 to 90 cm depth. These results suggest that C accumulation deep in the soil profile may be typical in midwestern cropping systems. Deep sampling to ≥100 cm is needed to capture the complete picture of soil C dynamics to assess soil C accumulation potential.

Physical and chemical stabilization of soil organic matter in cropland ecosystems under rice–wheat, maize–wheat and cotton–wheat cropping systems in northwestern India

This article examines the impact of rice–wheat, maize–wheat and cotton–wheat cropping systems on total (TOC), labile and stable organic carbon (C) pools, aggregate stability and distribution of organic C in different size aggregates and the mineral fraction (silt + clay) of soil. The rice–wheat soils had significantly (p < .05) lower TOC concentration (4.46 ± 0.15 g C kg−1) compared with the other two cropping systems. Similarly, water-extractable organic C (WEOC, ∼0.48% of TOC), hot-water-soluble C (HWC, ∼5.5% of TOC) and microbial biomass C (MBC, ∼4.2% of TOC) were significantly lower in soils under rice–wheat compared to the other systems. The formation of water-stable aggregates (WSA) was related to the silt + clay (<0.053 mm) fraction of soils. As the silt + clay fraction increased, the proportion of macro-aggregates (>0.25 mm) increased with a concomitant decrease in the proportion of micro-aggregates (<0.25 mm). The carbon preservation capacity (CPC) of macro-aggregates (CPCMacA), micro-aggregates (CPCMicA) and total water-stable aggregates (CPCWSA) was significantly lower in rice–wheat soils compared with the other systems. The CPCMacA, mineral (silt + clay)-associated C (MinAC) and sodium hypochlorite oxidizable C (NaOCl-C) increased with an increase in the proportion of macro-aggregates and the mineral fraction of soils. A linear increase in the stable C pool ((silt + clay)-C and NaOCl-C) and soils’ silt + clay content implies that soils’ fine fraction was the principal mechanism of textural control on soil organic matter (SOM) stabilization.

Assessing the impact of water treatment residuals and rice straw compost on soil physical properties and wheat yield in saline sodic Soil

ABSTRACT Rice straw compost (RC) and water treatment residuals (WTR) can improve both organic wastes recycling and soil physical properties of salt-affected soils. Therefore, the aim of this study was to test the effect of RC and its mixture with WTR on some physical properties of the saline-sodic soil, and wheat yield. The treatments were RC, WTR, and RC + WTR mixture at rates of 12 and 24 t ha−1. The results indicated that the application of RC alone or combined with WTR significantly increased drainable porosity (DP), total porosity (TP), mean weight diameter (MWD) and total water-stable aggregates (WSA) as compared to control. The increase in soil DP under the 24 t of WTR ha−1 was 64.7% greater than the control treatment. The mixtures of RC +WTR gave better results in increasing the dry weight and grain yield, especially the rate of 24 t of RC +WTR (1:2) ha−1 soil as compared to adding them individually. The experimental results concluded that the WTR + RC mixture can be used as a promising strategy to increase wheat yield and improve the efficiency of recycled rice straw and WTR on the physical properties of saline-sodic soils.

Effect of conservation tillage and rice-based cropping systems on soil aggregation characteristics and carbon dynamics in Eastern Indo-Gangetic Plain

Traditional rice–wheat cropping system, which follows wet puddling in rice and conventional tillage in wheat, is deteriorating soil health resulting yield stagnation in the Indo-Gangetic Plains of South Asia. Conservation agriculture which endorses minimum soil disturbance, residue retention and crop diversification not only improves soil health but also reduces the CO2 concentration in atmosphere. We hypothesized that adoption of conservation agriculture could improve the soil health and soil organic carbon in comparison with conventional practices. A field experiment was conducted during 2012–2015 to observe the effects of different tillage practices and cropping systems on soil aggregation and carbon dynamics. The experiment comprised of three cropping systems, viz. rice–wheat, RW; rice–maize, RM; rice–lentil, RL, practiced in three tillage practices, viz. conventional tillage, CT; reduced tillage, RT; reduced tillage with 30% residue, RT30 in factorial randomized block design. Adoption of RT and RT30 resulted in higher macroaggregate content of 51.7 and 61.2%, respectively, in comparison with CT. Total water stable aggregates and mean weight diameter (MWD) of aggregates were considerably higher in RT and RT30 treatments, and the effect was most pronounced in the upper 0–15 cm soil layer. The rice–maize cropping system registered the highest macroaggregate content, water stable aggregates (WSA) and MWD of 55.6%, 80.0% and 2.28 mm, respectively, in the upper surface soil. The rice–maize cropping systems under RT30 recorded the highest total soil organic carbon (SOC) stock (51.0 Mg ha−1) in comparison with other systems after 3 years of experimentation. Reduced tillage and residue management resulted in positive changes in soil infiltration rate. The effect of tillage operations and cropping systems on different soil properties (aggregate distribution, WSA, MWD and geometric mean diameter of aggregates, SOC stock, Bulk density) was mostly limited to surface layer of soil.

Effects of tillage, crop establishment and diversification on soil organic carbon, aggregation, aggregate associated carbon and productivity in cereal systems of semi-arid Northwest India

Intensive tillage based management practices are threatening soil quality and systems sustainability in the rice-wheat belt of Northwest India. Furthermore, it is accentuated with puddling of soil, which disrupts soil aggregates. Conservation agriculture (CA) practices involving zero tillage, crop residue management and suitable crop rotation can serve as better alternative to conventional agriculture for maintaining soil quality. Soil organic carbon is an important determinant of soil quality, playing critical role in food production, mitigation and adaptation to climate change as well as performs many ecosystem functions. To understand the turnover of soil carbon in different forms (Total organic carbon-TOC; aggregate associated carbon-AAC; particulate organic carbon- POC), soil aggregation and crop productivity with different management practices, one conventional agriculture based scenario and three CA based crop management scenarios namely conventional rice-wheat system (Sc1), partial CA based rice-wheat-mungbean system (Sc2), full CA-based rice-wheat-mungbean system (Sc3) and maize-wheat-mungbean system (Sc4) were evaluated. TOC was increased by 71%, 68% and 25% after 4 years of the experiment and 75%, 80% and 38% after 6 years of the experiment in Sc4, Sc3 and Sc2, respectively, over Sc1 at 0–15 cm soil depth. After 4 years of the experiment, 38.5% and 5.0% and after 6 years 50.8% and 24.4% improvement in total water stable aggregates at 0–15 and 15–30 cm soil depth, respectively was observed in CA-based scenarios over Sc1. Higher aggregate indices were associated with Sc3 at 0–15 cm soil depth than others. Among the size classes of aggregates, highest aggregate associated C (8.94 g kg−1) was retained in the 1-0.5 mm size class under CA-based scenarios. After 6 years, higher POC was associated with Sc4 (116%). CA-based rice/maize system (Sc3 and Sc4) showed higher productivity than Sc1. Therefore, CA could be a potential management practice in rice-wheat cropping system of Northwest India to improve the soil carbon pools through maintaining soil aggregation and productivity.

Distribution of N-mineralizing Enzymes in Soil Aggregate Fractions over 46 Years Application of Inorganic and Organic Fertilizers in a Tropical Rice-Rice System

The stability of enzymes in soil has been attributed to enzyme association with organic matter and the protection provided within soil aggregates. Enzymes namely urease, amidase and protease significantly affects nitrogen (N) mineralization and their assessment is crucial to study the nutrient cycling. Therefore, the objective of this study was to evaluate the hypothesis that the long-term application of farmyard manure (FYM) and inorganic fertilizers (N-nitrogen; P-phosphorus; K-potassium) impact the distribution pattern of enzymes namely, urease, amidase and protease in different fractions of water stable soil aggregates, and whole soil at 0–15 cm and 15–30 cm soil depth. The treatments comprised of unfertilized control and different combinations of inorganic fertilizers and FYM viz. control, N, NP, NK, NPK, FYM, FYM+N, FYM+NP, FYM+NK and FYM+NPK. A significant difference in soil aggregate size distribution was observed at two sampling depths. Total water stable aggregates (WSA) ranged between 69.8–91.2% in which 0.1–0.053 mm aggregate fraction contributed (2.11–3.87%), whereas 0.25–0.5 mm aggregate fraction was having the highest (27.3–32.6%) contribution. The activities of three enzymes in whole soil as well in aggregate fractions were lowest in control and highest in FYM+NPK except for amidase, which was having highest activity in FYM alone treatment. Activities of all the three enzymes were highest in aggregate fraction of 5–2 mm. Activities of three enzymes in whole soil as well as in aggregate fractions were lower at 15–30 cm compared to 0–15 cm soil depth. It may be concluded from this study that long-term addition of FYM alone or in combination with inorganic fertilizer increases the macroaggregate (5–2 mm) and hence the overall activities of N mineralization enzymes.

Interrelationship of biomass yield, carbon input, aggregation, carbon pools and its sequestration in Vertisols under long-term sorghum-wheat cropping system in semi-arid tropics

We investigated dynamics of soil organic carbon (SOC) i.e. total soil organic carbon (TOC), oxidisable organic carbon (OC) and its different pools viz. very labile (CVL), labile (CL), less labile (CLL) and non-labile (CNL), and various sized aggregate associated carbon (AAC) and also its sequestration along depth (0-0.15, 0.15-0.30, and 0.30 -0.45 m) in a typical Vertisols under hot semi-arid agro-climatic conditions. Such dynamics were studied under different soil management practices viz., control, NPK (100% recommended doses of N, P and K fertilizers, RDF), NPK + FYM (50% N and whole of the RDF and 50% N through FYM) and fallow using a 28 year old long-term experiment with sorghum (Sorghum bicolour L.) – wheat (Triticum aestivum L.) cropping system. On average, a higher proportion (70% of TOC) of SOC was found in passive pool (less labile + non labile) than active one (very labile + labile) throughout the profile. The proportion of active pool was, however, higher under balanced (NPK) and integrated nutrient management practices (NPK + FYM) over the others followed. Long-term intensive cropping with NPK (15.1%) and NPK + FYM (22%) caused a net enrichment in SOC stock over the control. To offset the loss of C and maintain the SOC level, a critical amount of 0.96 Mg C ha−1yr−1 was needed to be incorporated into the soil. Out of the total water stable aggregates (WSA), mesoaggregates (0.25–2.0 mm) predominated (73.6%) followed by micro (16.4%), and macroaggregates (10.7%) at surface soil. Amount of carbon associated with different sized aggregates had the following trend: mesoaggregate (52.3%) > coarse microaggregate (13.7%)> coarse macroaggregate (13.5%)> (silt + clay) sized aggregate (13.1%)> fine microaggregate (12.2%). Balanced fertilization with organics thus provided not only higher yield but also increased C sequestration in Vertisols even with intensive cropping of sorghum-wheat system under hot semi-arid conditions.

Manure and Fertilizer Application Effects on Aggregate and Mineral-Associated Organic Carbon in a Loamy Soil under Rice-Wheat System

ABSTRACTThe study was conducted to investigate the aggregate stability and distribution of organic carbon (C) in different-sized aggregates and mineral fractions in a loamy soil under rice-wheat system with continuous application of fertilizer nitrogen, phosphorus and potassium (NPK), farmyard manure (FYM), N+FYM and NPK+FYM, compared with unfertilized control. Macro-aggregates comprised 37.1–49.3% of the total water-stable aggregates (WSAs), compared with 23.3–30.3% as micro-aggregates. Application of inorganic fertilizers and FYM significantly increased the proportion of macro-aggregates, which were linearly related to total organic C (TOC). Organic C concentration in coarse macro-aggregates (CMacA) was higher than the micro-aggregates (CMicA). Application of FYM significantly increased the concentration of organic C in different-sized aggregates and mineral fraction, compared with the unfertilized control. Averaged across treatments, mineral-associated C comprised 26% of TOC. Macro-aggregates, on an average, constituted 66–68% of C preservation capacity of WSA. The amount of TOC sequestered was higher when NPK+FYM was applied together.

Twelve Years of Stover Removal Increases Soil Erosion Potential without Impacting Yield

Corn (Zea mays L.) stover (non-grain aboveground biomass) in the US Corn Belt is used increasingly for livestock grazing and co-feed and for cellulosic bioenergy production. Continuous stover removal, however, could alter long-term agricultural productivity by affecting soil organic C (SOC) and soil physical properties, indicators of soil fertility and erosion potential. In this study, we showed that 12 consecutive yr of 55% stover removal did not affect mean grain yields at any N fertilizer rate (4.5, 6.3, and 6.0 Mg ha−1 for 60, 120, and 180 kg N ha−1 yr−1, respectively) in a marginally productive, rainfed continuous corn system under no-till (NT). Although SOC increased in the top 30 cm of all soils since 1998 (0.54–0.79 Mg C ha−1 yr−1), stover removal tended to limit SOC gains compared with no removal. Near-surface soils (0–5-cm depth) were more sensitive to stover removal and showed a 41% decrease in particulate organic matter stocks, smaller mean weight diameter of dry soil aggregates, and lower abundance of water-stable soil aggregates compared with soils with no stover removal. Increasing N fertilizer rate mitigated losses in total water-stable aggregates in near-surface soils related to stover removal. Collectively, however, our results indicated soil structure losses in surface soils due to lower C inputs. Despite no effect on crop yields and overall SOC gains with time using NT management, annually removing stover for 12 yr resulted in a higher risk of wind and water erosion at this NT continuous corn site in the western Corn Belt.

Groundcover Management System and Nutrient Source Impacts on Soil Quality Indicators in an Organically Managed Apple (Malus ×domestica Borkh.) Orchard in the Ozark Highlands

The highly weathered, mineral, and often eroded and acidic soils of the Ozark Highlands region of northwest Arkansas generally have low soil organic matter (SOM) concentrations as a result of rapid organic matter turnover rates in the warm, moist climate. Orchard management practices that can improve SOM may also improve other soil quality-related variables for sustained production, which is an explicit goal for the National Organic Program (NOP). Therefore, beginning in Mar. 2006 and continuing for seven seasons, annual applications of municipal green compost, shredded office paper, wood chips, and mow-blow grass mulch groundcover management systems (GMS) in combination with composted poultry litter, commercial organic fertilizer, or a non-fertilized control as a nutrient source were implemented to evaluate their ability to alter near-surface soil quality in a newly established, organically managed apple orchard in the Ozark Highlands region of northwest Arkansas. The SOM concentration in the top 10 cm averaged 1.5% across all treatments at orchard establishment in 2006, but by 2012, SOM concentration had increased in all GMS and more than doubled to 5.6% under green compost. Similarly, soil bulk density in the top 6 cm, which averaged 1.34 g·cm−3 among treatment combinations in 2006, decreased in all GMS by 2012. Either green compost or shredded paper had the largest concentration of total water-stable aggregates across all aggregate size classes in the top 7.5 cm, whereas no differences among GMS were observed in the 7.5- to 15-cm soil depth. Green compost applied alone or in combination with commercial fertilizer had the largest estimated plant-available water (17.9% v/v) among all treatment combinations. Many soil quality-related variables measured in the various organic GMS had numerically greater values compared with an adjacent conventionally managed orchard on the same soils. Implementation of these GMS appears to provide apple producers in the Ozark Highlands and similar regions a tangible means of meeting NOP requirements for improving soil quality concurrent with production of certified organic crops. The findings also have implications for conventionally managed orchards, which have maintaining or improving soil quality as a management goal.

Tillage and residue management effects on soil aggregation, organic carbon dynamics and yield attribute in rice–wheat cropping system under reclaimed sodic soil

Conservation tillage and residue management are the options for enhancing soil organic carbon stabilization by improving soil aggregation in tropical soils. We studied the influence of different combinations of tillage and residue management on carbon stabilization in different sized soil aggregates and also on crop yield after 5 years of continuous rice–wheat cropping system on a sandy loam reclaimed sodic soil of north India. Compared to conventional tillage, water stable macroaggregates in conservation tillage (reduced and zero-tillage) in wheat coupled with direct seeded rice (DSR) was increased by 50.13% and water stable microaggregates of the later decreased by 10.1% in surface soil. Residue incorporation caused a significant increment of 15.65% in total water stable aggregates in surface soil (0–15cm) and 7.53% in sub-surface soil (15–30cm). In surface soil, the maximum (19.2%) and minimum (8.9%) proportion of total aggregated carbon was retained with >2mm and 0.1–0.05mm size fractions, respectively. DSR combined with zero tillage in wheat along with residue retention (T6) had the highest capability to hold the organic carbon in surface (11.57gkg−1 soil aggregates) with the highest stratification ratio of SOC (1.5). Moreover, it could show the highest carbon preservation capacity (CPC) of coarse macro and mesoaggregates. A considerable proportion of the total SOC was found to be captured by the macroaggregates (>2–0.25mm) under both surface (67.1%) and sub-surface layers (66.7%) leaving rest amount in microaggregates and ‘silt+clay’ sized particles. From our study, it has been proved that DSR with zero tillage in wheat (with residue) treatment (T6) has the highest potential to secure sustainable yield increment (8.3%) and good soil health by improving soil aggregation (53.8%) and SOC sequestration (33.6%) with respect to the conventional tillage with transplanted rice (T1) after five years of continuous rice–wheat cropping in sandy loam reclaimed sodic soil of hot semi-arid Indian sub-continent.

Soil aggregation and distribution of carbon and nitrogen in different fractions after 41 years long-term fertilizer experiment in tropical rice–rice system

Inorganic fertilizers and manure application can alter the aggregate distribution as well as aggregate associated organic carbon and nitrogen. It is not fully understood how long term addition of carbon (C) and nitrogen (N) through biomass, farm yard manure (FYM) and inorganic fertilizers are distributed in soil aggregates in a tropical rice–rice system. Therefore, the objectives of this study were to investigate the long-term effects of FYM and inorganic fertilizer in a rice–rice system on (i) distribution of water stable aggregates in the soil, and (ii) amount of total soil organic carbon (TOC), total N and C/N ratio in different aggregate fractions. The total water stable aggregates (WSA) ranged from 71.6% under control to 91.1% under NPK+FYM in the surface soil (0–15cm). The incorporation of FYM increased the macroaggregates (5–2mm) by 165.3% and mesoaggregates by 130.7% (2–1mm) and 282.8% (1–0.5mm) over control in 0–15cm soil layer. Mean weight diameter (MWD), varied from 0.43 to 0.78 in 0–15cm and from 0.40 to 0.72 in 15–30cm soil layer. MWD was higher under FYM treated plots than inorganic fertilizer alone and unfertilized control plots. Irrespective of treatment, macroaggregates (5–2mm) had the highest (4.13–14.03gkg−1) and microaggregate fraction (0.25–0.1mm) had the least (3.70–8.89gkg−1) TOC content in the 0–15cm soil layer. The application of FYM either alone or in combination with inorganic fertilizers significantly increased the accumulation of TOC in all aggregate fractions over control, however, the effect was more pronounced in macroaggregates fraction 5–2mm and microaggregate fraction 0.1–0.053mm. The combined application of inorganic fertilizers and FYM resulted in an increase in total N content which ranged from 0.43 to 1.0gkg−1 in 5–2mm and from 0.09 to 0.44gkg−1 in 0.25–0.1mm aggregate fractions. The highest C:N ratio was recorded in aggregate fraction of 0.1–0.053mm irrespective of treatment, whereas aggregate fraction of 0.5–0.25mm had the least C:N ratio. A higher C:N ratio was observed in 15–30cm than 0–15cm soil layer. Hence it was concluded that the long-term application of FYM resulted in C and N accumulation in bulk soil and aggregates, but the accumulation pattern was dependent on aggregate size.

Soil aggregation and carbon and nitrogen stabilization in relation to residue and manure application in rice–wheat systems in northwest India

Soil organic matter (SOM), besides influencing carbon (C) transfer between soils and atmosphere, impacts soil functional ability and its response to environmental and anthropogenic influences. We studied the impact of continuous application of rice straw and farmyard manure (FYM) either alone or in conjunction with inorganic fertilizers on aggregate stability and distribution of C and nitrogen (N) in different aggregate fractions after 7 years of rice–wheat cropping on a sandy loam soil. Macroaggregates (>0.25 mm) constituted 32.5–54.5% of total water stable aggregates (WSA) and were linearly related (R 2 = 0.69) to soil organic carbon content. The addition of rice straw and FYM significantly (P < 0.05) improved the formation of macroaggregates with a concomitant decrease in the proportion of microaggregates at all the three sampling depths (0–5, 5–10 and 10–15 cm). Macroaggregates had higher C and N density as compared to microaggregates. Application of rice straw and FYM improved C and N density in different aggregate sizes and the improvement was greatest in plots that received both rice straw and FYM each year. Application of FYM along with inorganic fertilizer resulted in a net C sequestration of 0.44 t ha−1 in the plough layer after 7 years of rice–wheat cropping. Carbon sequestration was greater (1.53 t ha−1) when both rice straw and FYM along with inorganic fertilizers were applied annually. It is concluded that addition of rice straw and FYM in rice–wheat system improves soil aggregation and enhances C and N sequestration in macroaggregates. This will help in sustainable rice–wheat productivity in the region.

Soil aggregation and distribution of carbon and nitrogen in different fractions under long-term application of compost in rice–wheat system

Soil organic matter improves the physical, chemical and biological properties of soil, and crop residue recycling is an important factor influencing soil organic matter levels. We studied the impact of continuous application of rice straw compost either alone or in conjunction with inorganic fertilizers on aggregate stability and distribution of carbon (C) and nitrogen (N) in different aggregate fractions after 10 cycles of rice–wheat cropping on a sandy loam soil at Punjab Agricultural University research farm, Ludhiana, India. Changes in water stable aggregates (WSA), mean weight diameter (MWD), aggregate-associated C and N, total soil C and N, relative to control and inorganically fertilized soil were measured. Total WSA were significantly ( p = 0.05) higher for soils when rice straw compost either alone or in combination with inorganic fertilizers was applied as compared to control. The application of rice straw compost either alone or in combination with inorganic fertilizers increased the macroaggregate size fractions except for 0.25–0.50 mm fraction. The MWD was significantly ( p = 0.05) higher in plots receiving rice straw compost either alone at 8 tonnes ha −1 (0.51 mm at wheat harvest and 0.41 mm at rice harvest) or at 2 tonnes ha −1 in combination with inorganic fertilizers (0.43 and 0.38 mm) as compared to control (0.34 and 0.33 mm) or inorganically fertilized plots (0.33 and 0.31 mm). The macroaggregates had higher C and N density compared to microaggregates. Application of rice straw compost at 2 tonnes ha −1 along with inorganic fertilizers (IN + 2RSC) increased C and N concentration significantly over control. The C and N concentration increased further when rice straw compost at 8 tonnes ha −1 (8RSC) was added. It is concluded that soils can be rehabilitated and can sustain the soil C and N levels with the continuous application of rice straw compost either alone or in combination with inorganic fertilizers. This will also help in controlling the rising levels of atmospheric carbon dioxide.

Tillage and drainage impact on soil quality: I. Aggregate stability, carbon and nitrogen pools

Effects of two tillage treatments, tillage (T) with chisel plough and no-till (NT), were studied under un-drained and drained soil conditions. Soil physical properties measured were bulk density ( ρ b), total porosity (ƒ t), water stable aggregates (WSA), geometric mean diameter (GMD), mean weight diameter (MWD), organic carbon (OC) and total N concentrations in different aggregate size fractions, and total OC and N pools. The experiment was established in 1994 on a poorly drained Crosby silt loam soil (fine mixed, mesic, Aeric Ochraqualf) near Columbus, Ohio. In 2007, soil samples were collected (0–10, 10–20, and 20–30 cm) from all treatments and separated into six aggregate size classes for assessing proportions of macro (5–8, 2–5, 1–2, 0.5–1, 0.25–0.5) and micro (<0.25 mm) aggregates by wet sieving. Tillage treatments significantly ( P ≤ 0.05) influenced WSA, MWD, and GMD. Higher total WSA (78.53 vs. 58.27%), GMD (0.99 vs. 0.68 mm), and MWD (2.23 vs. 0.99 mm) were observed for 0–10 cm depth for NT than T treatments. Relative proportion of macro-aggregates (>0.25-mm) was also more in NT than T treatment for un-drained plots. Conversely, micro-aggregates (<0.25-mm) were more in T plots for both drained and un-drained treatments. The WSA, MWD and GMD decreased with increase in soil depth. The OC concentration was significantly higher ( P ≤ 0.05) in NT for un-drained ( P ≤ 0.01) treatment for all soil depths. Within macro-aggregates, the maximum OC concentrations of 1.91 and 1.75 g kg −1 in 1–2 mm size fraction were observed in NT for un-drained and drained treatments, respectively. Tillage treatments significantly ( P < 0.01) affected bulk density ( ρ b), and total porosity ( f t) for all soil depths, whereas tillage × drainage interaction was significant ( P < 0.01) for 10–20 and 20–30 cm depths. Soil ρ b was negatively correlated ( r = −0.47; n = 12) with OC concentration. Tillage treatments significantly affected ( P ≤ 0.05) OC pools at 10–20 cm depth; whereas drainage, and tillage × drainage significantly ( P ≤ 0.05) influenced OC pools for 0–10 cm soil layer. The OC pool in 0–10 cm layer was 31.8 Mg ha −1 for NT compared with 25.9 Mg kg −1 for T for un-drained treatment. In comparison, the OC pool was 23.1 Mg ha −1 for NT compared with 25.2 Mg ha −1 for T for the drained plots. In general, the OC pool was higher in NT system, coupled with un-drained treatment than in drained T plots. The data indicate the importance of NT in improving the OC pool.

Biomass of fine roots and its relationship with water-stable aggregates in a composite ecosystem of triploid Populus tomentosa in the conversion of farmland to forest

A study on the biomass of fine roots and its relationship with water-stable aggregates (WSA) was conducted in two herbaceous models, triploid Populus tomentosa + Lolium multiflorum (TL) and triploid P. tomentosa + natural grass (TN). Both of the model triploid P. tomentosa stands were four years old converted from agriculture. Unconverted steep slope farmland was used as a control site. Results showed that the biomass of fine roots (⩽ 1 mm) in different layers varied in the following descending order: upper layer, middle layer and lower layer, at approximate ratios of 50:30:20. The average annual biomass of fine roots in ryegrass was twice that of the mixed natural grass-forest land. The total amount of natural grass roots was 4.4 times that of the ryegrass model. Water-stable aggregates of the upper, middle and lower layers and the unconverted farmland did not show any significant differences, whereas the amounts of water-stable aggregates of big-particles in the upper and middle layers were much larger than those of unconverted lands. The amounts of water-stable aggregates of natural grass-forest lands (TN model) were higher than those of managed grass-forest lands (TL model). Two-way analysis of variance indicated that fine roots (≤ 1 mm) could significantly enhance water-stable aggregates and total water-stable aggregates. We conclude that the program of converting agricultural lands to forest-grass lands is an effective way in improving soil anti-erosion capability.

Chemical properties of soil and water-stable aggregates after sixty-seven years of cropping to spring wheat

Three non-replicated, unfertilized, dryland grain rotations—continuous wheat, wheat-fallow, and wheat-wheat-fallow—were established in 1912 on a Dark Brown Chernozemic (Typic Haploboroll) soil. The effect of long-term cropping on the chemical constituents of total water-stable aggregates was assessed. There was a loss in percentage of total water-stable aggregates and a shift in aggregate size distribution with time. Together with an increase in the 100 μm diameter fraction, there was an increase in the sand component of this fraction. These sand particles are probably held together by alkaline-soluble, acid-insoluble organic matter. Organic carbon, polysaccharides, polyuronides, phenols, and chloroform/methanol-extractable organic matter were all associated with the >250 μm diameter fractions. Although the aggregates had generally the same suite of aliphatic carboxylic acids, the relative proportions changed with cultivation.