Proportion Of Stable Aggregates Research Articles

Roots of Cleistogenes songorica Improved Soil Aggregate Cohesion and Enhance Soil Water Erosion Resistance in Rainfall Simulation Experiments

Native grasses that have acceptable forage yield and quality can play an important role in the sustainable development and protection of soil ecosystem. In this study, we investigate a native grass of northern China, Cleistogenes songorica, showing promise for erosion control. We used a rainfall simulation method to compare the effects of C. songorica roots and tall fescue roots (Festuca arundinacea) on soil erosion in sandy loam field plots with irrigation during establishment in 2011 and under mild or severe drought treatments in 2012 and 2013. Root length (RL), root diameter (RD), soil bulk density (SBD), soil field capacity (FC), sediment yield (SY), and root biomass (RB) of each soil monolith were sampled in the topsoil layer (0–10 cm) with a rectangular geotome. The proportion of stable aggregates in soil and the soil anti-scouring properties were also evaluated. C. songorica had higher RD than tall fescue throughout the experiment and evolved higher RL and RB by 2013. Both C. songorica and tall fescue enhanced the erosion resistance of soil, but C. songorica stabilized soil more effectively than did tall fescue. The proportion of stable soil aggregates was greater in C. songorica plots than in tall fescue grassland under mild drought. The present study shows that C. songorica has great potential to be one of the biological resources for soil erosion resistance, water and soil conservation in arid and semi-arid areas.

Lasting effects of biosolids in agroecosystems

Lasting effects of biosolids in agroecosystems

Effects of grazing on soil physical properties and soil erodibility in semiarid grassland of the Northern Loess Plateau (China)

Grazing animals provide a livelihood for farmers, but they may also produce adverse environmental effects. We investigated whether grazing leads to deterioration of soil physical properties that subsequently increases topsoil erodibility. We sampled three sites (an ungrazed grassland, a continuously grazed grassland, and a track trampled by stock) on the northern Loess Plateau of China. The bulk density, water content, proportion of stable aggregates, infiltration rate, and resistance to scouring were determined for each soil sample. The results showed that the track had the highest soil bulk density and the lowest soil water content, proportion of stable aggregates, infiltration rate, and ability to resist scouring. The ungrazed plots had the best results for these parameters, in terms of reduced erosion. Soil bulk density and the proportion of stable aggregates differed significantly with depth beneath the track. However, the effect of depth on water content, infiltration rate, and the soil resistance to scouring was not significant at any sampling site. The ability of the soil to resist scouring was negatively correlated with the soil's bulk density and positively correlated with the soil's water content, infiltration rate, and proportion of stable aggregates. Thus, soil physical properties played an important role in determining soil erodibility. Grazing and trampling by livestock therefore appear to cause deterioration of soil physical properties and to increase soil erodibility.

Effect of root mucilage and modelled root exudates on soil structure

SummaryPlant roots release in the rhizosphere diverse organic materials which may have different effects on soil structure. We have evaluated the effect of natural and modelled root‐released materials on soil aggregates and the biodegradation of carbon from roots in the soil. The effects of root mucilage from maize and of a modelled soluble exudate were compared with those of simple compounds (glucose, polygalacturonic acid). For all treatments, soil was amended with 2 g C kg−1 soil and incubated for 30 days at 25°C. The biodegradation of mucilage was similar to that of polygalacturonic acid, and slower than the decomposition of modelled exudates and glucose. Addition of all substrates increased the stability of aggregates, but the duration of this effect depended on the chemical nature of the material. Compared with the control, the proportion of stable aggregates after 30 days of incubation was multiplied by 3.8 for root mucilage, by 4.2 for modelled soluble exudates, by 2.5 for polygalacturonic acid and by 2.0 for glucose. The different fractions of root exudates in the rhizosphere evidently affected the aggregate stability.

Soil Physical Properties and Moisture Content Affected by Site Preparation in the Afforestation of a Semiarid Rangeland

Revegetation of arid regions is primarily water‐limited. To test the impact of several afforestation site preparation methods on the physical properties and the moisture content of the soil, a factorial experiment was conducted in a degraded semiarid rangeland of southeastern Spain. The land preparation treatments evaluated were terracing (mechanical or manual) and organic amendment (with or without urban solid refuse, USR). Terracing negatively affected some of the physical characteristics of the surface soil, such as the proportion of stable aggregates (21–33% decrease). Mechanical terracing increased soil water storage up to 40% more than manual terracing. The addition of USR counteracted many of the negative effects of terracing on soil physical properties and significantly increased soil moisture, particularly in the mechanical terraces (up to 40% increase compared with the nonamended treatment). The beneficial effects of the organic amendment on soil water content in the mechanical terraces persisted 4 yr after the single addition of the USR. The combination of mechanical terracing and USR addition significantly enhanced soil water availability, which is the most likely factor for the enhanced plant survival and growth seen in this study.

Changes in soil organic C, microbial C and aggregate stability under continuous maize and cereal cropping, and after restoration to pasture in soils from the Manawatu region, New Zealand

Soil compaction can be a major limitation to continuous maize production on the heavier-textured soils of the Manawatu region, New Zealand. A survey was undertaken of commercially-operated farms that were producing continuous maize using conventional mouldboard ploughing and cultivation methods. The effects of cultivation on the proportions of water-stable macroaggregates, total organic C content, microbial biomass C and soil respiration were measured in the predominant soil type, a poorly-drained Kairanga silty clay loam (Typic Haplaquept). Three other regional soil types, a Manawatu silt loam (well drained), Kairanga silt loam (poorly drained) and Moutoa humic clay (very poorly drained) were incluced for comparison. The effects of cropping with wheat or barley, and the recovery of the soils after restoration to pasture, were also measured. Continuous cultivation with maize on the Kairanga silty clay loam for up to 11 years decreased the total C content in the top 20 cm of soil by 21%, microbial C by 49% and water-stable aggregates (greater than 2 mm) by 54% compared with the levels under long-term permanent pasture. Losses on cultivation of pastures were greater on Manawatu silt loam with decreases of 49% in organic C, 60% in microbial C and 98% of the greater than 2 mm aggregates. Changes were much less pronounced on the Moutoa soil with a greater initial organic matter content, and the soil rapidly established new, only slightly lower, equilibria. Cultivation for barley or wheat had a less detrimental effect than cultivation for maize on the total organic and microbial C contents and aggregate stability of Kairanga silty clay loam. There was a strong linear relationship between the decline in the proportion of stable aggregates and the loss of microbial C and organic C in the top 10 cm of cultivated Kairanga soil. The relationship was stronger between microbial C and aggregate stability ( R 2 = 77.8%) than total organic C and aggregate stability ( R 2 = 64%), but was only valid when soil organic C was declining, and was not significant in the soil at the 10–20 cm depth. Re-establishment of pasture caused a more rapid recovery in microbial biomass C than total C, and increased the proportion of organic C comprised of microbial C. However, recovery of the total organic and microbial C pools and aggregate stability was very variable, and after 4 years of pasture none of the sites had re-established the levels found under permanent pasture. The previous cropping history of these soils before being returned to pasture, rather than the organic or microbial C content, appeared to be of greater importance in controlling the aggregate stability characteristics.