Effect of Organic Inputs on Strength and Stability of Soil Aggregates Under Rice-Wheat Rotation

Abstract

A b s t r a c t. The study aims to elucidate the impact of organic inputs on strength and structural stability of aggregates in a sandy loam soil. Tensile strength, friability and water stability of aggregates, and the carbon contents in bulk soil and in large macro (>2 mm), small macro (0.25-2 mm), micro (0.053-0.25 mm) and silt+clay size (<0.053) aggregates were evaluated in soils from a long-term experiment with rice-wheat rotation at Modipuram, India, with different sources and amounts of organic C inputs as partial substitution of N fertilizer. Addition of organic substrates significantly improved soil organic C contents, but the type and source of inputs had different impacts. Tensile strength of aggregates decreased and friability increased through organic inputs, with a maximum effect under green gram residue (rice)-farmyard manure (wheat) substitution. Higher macroaggregates in the crop residue-and farmyard manure-treated soils resulted in a higher aggregate mean weight diameter, which also had higher soil organic C contents. The bulk soil organic C had a strong relation with the mean weight diameter of aggregates, but the soil organic C content in all aggregate fractions was not necessarily effective for aggregate stability. The soil organic C content in large macroaggregates (2-8 mm) had a significant positive effect on aggregate stability, although a reverse effect was observed for aggregates <0.25 mm. Partial substitution of nitrogen by organic substrates improved aggregate properties and the soil organic C content in bulk soil and aggregate fractions, although the relative effect varied with the source and amount of the organic inputs.K e y w o r d s: tensile strength, friability, aggregates, soil organic C, rice-wheat rotation mean weight diameter INTRODUCTIONSustainability of the rice-wheat system in the indo-gangetic plains (IGP) is crucial for meeting country food demand, and is also at the centre of global food security (Ladha et al., 2003a). This sustainability is arguably at stake, partly due to the staggering productivity, and partly due to degradation of soil quality (Ladha et al., 2003b). Continuous use of imbalanced fertilizers under intensive rice-wheat cultivation over the years had negative impacts on soil structure, organic carbon and nutrient supplying capacity of the soils (Bhandari et al., 2002;Regmi et al., 2002). Addition of organic inputs as a partial substitution of N has been one of viable options in restoring the soil quality and subsequently sustaining the system productivity.As the soil is collectively made of aggregates, the study at the single structural unit or aggregate has been useful to evaluate the soil response to management (Blanco-Canqui et al., 2005). Since the rice-wheat system involves two contrasting edaphic environments, the role of soil aggregation is of special importance. The mechanical properties of aggregates are clearly indicative of soil structural condition determining soil functions for plant growth. Tensile strength (TS), a fundamental property of ...

Effect of Organic Inputs on Strength and Stability of Soil Aggregates Associated Organic Carbon Concentration under Rice-Wheat Rotation in Indo-Gangetic Plain Zone of India

“…The capillary-wetted soil aggregates did not show any clear trends across the treatments. Das et al, (2014) observed that a large reduction (50-75%) in MWD was observed upon slaking, more in case of inorganic N treatments. Variation in MWD of capillarywetted aggregates was also less (3.5-4.5 mm).…”

“…Song et al, (2016) reported that compared to conventional tillage, the percentages of >2mm macro aggregates and water-stable macroaggregates in rice-wheat double-conservation tillage (zero-tillage and straw incorporation) were increased 17.22% and 36.38% in the 0-15 cm soil layer and 28.93% and 66.34% in the 15-30 cm soil layer, respectively. In surface soil (0-15cm), the maximum proportion of total aggregated carbon was retained with 0.25-0.106mm aggregates, and rice-wheat double-conservation tillage had the greatest ability to hold the organic carbon (33.64g kg −1 ) it is evident that the MBC contents in both surface and sub-surface soil were significantly higher in plots receiving 50% RDN as CF+50% RDN as FYM ( F 5 ) Aggregate-associated organic carbon Das et al, (2014) revealed that the long term application of organics increased aggregate associated C as compared in all aggregate size fractions; the highest increase was observed in plots receiving NPK and FYM in combination. Arthur et al, (2012) also indicate that post-tillage consolidation of soils developing into compact and denser aggregates is significantly reduced through addition of organic inputs.…”

“…The magnitude of change in pools of SOC in sub-surface (15-30 cm) soil was low as compared to the surface soil (0-15 cm). Das et al, 2014 found that the aggregate strength and density were lower with organic substitution (p<0.05) while water retention by aggregates at field capacity was 2-4% higher with organic inputs. Macro-aggregates (>0.25mm) constituted 58-92% of water stable aggregates and varied significantly among treatments and soil depths.…”

“…However, larger m M-C in organic treatments, especially with GR (rice)-FYM (wheat) is indicative of scope of long-term C protection within aggregates, which may be a possible indicator of C sequestration. Das et al, (2014) found that the density, tensile strength and friability of aggregates increased with soil depth but decreased with additional organic inputs. Treatment T 1 had the highest aggregate densities (1.82-1.91 Mg m -3 ) and strengths (127.2-171.6 kPa), but the lowest friability (0.10-0.15).…”

“…A reduced presence of macro aggregates (>0.25 mm) under TT was partly due to excessive tillage and heavy traffic, which hindered the soil biological activity (Tisdall and Oades, 1979). Bappa Das et al, (2014) revealed that the increased amounts of large (>2 mm) macroaggregate fractions in NPK + GR (rice) + FYM (wheat) and NPK + CR (rice and wheat) are associated with the very large MWD in these treatments. Similar trends are observed in other organic treatments, with a large amount of small macro-aggregate fractions, along with large macro-aggregates.…”