Percentage Of Water-stable Aggregates Research Articles

Long-term effects of biochar one-off application on soil physicochemical properties, salt concentration, nutrient availability, enzyme activity, and rice yield of highly saline-alkali paddy soils: based on a 6-year field experiment

Biochar application can alleviate the adverse effects of saline-alkali stress on crops. However, the long-term effects of one-off biochar application on soil physicochemical properties, salt concentration, nutrient availability, soil enzyme activities, and rice yield under highly saline-alkali paddy soils remain unclear. Here, a 6-year paddy field study was conducted in a saline-alkali paddy field using two nitrogen application levels (0 and 225 kg ha−1) and four biochar application rates [0 (T0), 1.5% (T1.5), 3.0% (T3.0), and 4.5% (T4.5) biochar, w/w]. The results showed that compared with T0, the bulk density (BD) under T1.5, T3.0, and T4.5 treatments significantly decreased by 11.21%, 16.33%, and 25.57%, while total porosity (Tp) and saturated hydraulic conductivity (Ks) increased by 19.15–27.34% and 3217.78–5539.83%, respectively. Biochar consistently improved soil macro-aggregates, mean weight diameter (MWD), and the percentage of water-stable aggregates (PWSA) over the years. Additionally, one-off application of biochar continuously reduced the soil Na+ concentration, Na+/K+ ratio, Na+/Ca2+ ratio, saturated paste extract (ECe), exchangeable sodium percentage (ESP), and sodium adsorption ratio (SARe). However, it reduced the pH in 2021 and 2022 only. It enhanced the concentration of K+, Ca2+, Mg2+, and cation exchange capacity (CEC) over the 6-year study, indicating its longer-term positive impact. Furthermore, the one-off biochar application, especially under high application rate treatments (T3.0 and T4.5), significantly and continuously improved nutrient availability and soil enzyme activities. However, alkali-hydrolysable nitrogen (AN) decreased in the initial year of biochar application. The grain yield of T1.5, T3.0, and T4.5 surpassed that of T0 by 116.38%, 141.24%, and 145.20%, respectively. Notably, the rice yield reached its peak with the treatment of 3.0% (w/w) in all 6 years of study period. These findings offered new perspectives on repairing and improving soil quality and production ability of highly saline-alkali paddy soils.Graphical

Evaluating the Soil Quality Indicators in Various Yield Zones of Pulses in Tamil Nadu, India

Background: In recent years, there is growing demand for pulses in Tamil Nadu and the government has implemented various schemes and programmes to promote cultivation. However, the evaluation and categorization of soils for pulse production is crucial in determining the suitability of land for pulse cultivation and offer improvement through the adoption of improved crop management practices. Methods: A systematic soil quality assessment survey was taken up during 2020-2022 in the major pulse growing blocks of Virudhunagar district viz., Sattur, Aruppukottai and Thiruchuli based on past ten years yield data and it was classified into three categories viz., low yielding ( less than 400 kg ha-1), medium (400 to 700 kg ha-1) and high yielding ( greater than 700 kg ha-1) categories. Three hundred samples were collected from these zones. Results: The positive effects of soil physical, chemical, and biological qualities on the yield of pulse crops were justified through the yield data of the high yielding zone which ranged from 769 to 989 kg ha-1 with an average pulse yield of 880 kg ha-1. This may be attributed to more favourable soil physical environment in terms of soil texture (sandy clay loam), higher mean percentage of water stable aggregates (51%) and a favourable pH of 7.52. These parameters coupled with lower bulk density (1.23 Mgm-3), optimum infiltration rate (1.76 cm hr-1) and maximum mean organic carbon status (1.38 mg kg-1) contributed to higher range of soil cation exchange capacity (28.7 to 47.2 cmol p+ kg-1). In addition, the presence of avilable nitrogen and phosphorus, potassium, sulphur and availability of mean micronutrient contents viz., DTPA iron and DTPA zinc resulted in better quality of these soils contributing to maximum pulse productivity in this zone. Soil respiration rate with mean respiration rate of 4.48 mg CO2 kg-1 d-1 in high yield category compared to that of 2.34 mg CO2 kg-1 d-1 in low yield category, which is well correlated with better soil organic matter content in the former than the latter group of soil. Therefore, this study formulates a clear understanding of the variations in soil quality parameters for adopting efficient nutrient management practices towards obtaining maximum productivity of pulse crops.

Soil Physico-Chemical Properties Change Across an Urbanity Gradient in Berlin

In this study the impacts of urbanity on physical soil properties were explored by measuring water stable aggregates, combined particle size, infiltration rate and hydrophobicity across an urban gradient. The use of a gradient allowed for the relative importance of different environmental drivers to be assessed. We sampled 54 sites across Berlin and used a pre-existing database of environmental variables to extract three main axes of variation relating to urbanity, soil nutrient content, and heavy metal content. These axes, along with site age, were used to explore the drivers of changes in physical properties across an urban landscape. The percentage of water stable aggregates was found to decrease with urbanity, whilst infiltration rate was found to increase. Hydrophobicity did not appear to be influenced by urbanity but interacted with both infiltration rate and water stable aggregates. Combined particle sizes in the soil were found to increase with urbanity. Our findings provide evidence for urbanity being an important driver of variation in physico-chemical soil properties, which has implications for the provision of ecosystem services by these soils.

50 years of continuous no-tillage, stubble retention and nitrogen fertilization enhanced macro-aggregate formation and stabilisation in a Vertisol

Farm management practices such as no-tillage, stubble retention, and nitrogen (N) application have a substantial potential to enhance soil aggregation in agricultural soils. This is especially important for Vertisols, which may experience extended waterlogging due to low infiltration rates and low hydraulic conductivity. We evaluated the long-term impacts of the tillage method (no tillage, NT, and conventional tillage, CT), stubble management practices (stubble retention, SR, or stubble burning, SB) and N-fertilization on aggregate size distribution, and distribution of total C and N within different aggregate-size fractions in a Vertisol. Soil samples were collected from 0–0.1 m depth at the Hermitage Research Station in Queensland, Australia, after 50 years of management. We found that the soil under NT with SR and 90 kg N fertilizer application (NTSRN90) contained the highest proportion of large macro-aggregates (31.0 %), the greatest mean weight diameter (MWD) (1.79 mm), and the highest percentage of water stable aggregates (WSA, 90.2 %), whilst the lowest values (3.15 %, 0.71 mm and 72.7 %, respectively) were found in the CTSBN0 treatment. Therefore, reducing soil disturbance by primary tillage operations (NT) and the retention of crop residues (SR) and fertilizer application stimulated the formation of soil macro-aggregates from micro-aggregates. Retention of higher amounts of residues to the system in the SR and N fertilized treatments increased the macro-aggregate occluded particulate organic C (POC) and N (PON), which likely provided loci for aggregate formation and binding agents for stabilisation. Larger aggregates stored more organic C and N, and had lower water retention at saturation (−10 kPa), than smaller aggregates or the silt + clay fraction, thus having the potential to reduce the frequency of waterlogging in the soil under NT, SR, and N fertilization. Therefore, long-term practice of no-tillage along with stubble retention and N fertilisation could significantly enhance the macro-aggregation of fine-textured Vertisols, with this then ensuring the sustainability of the agricultural production system by creating favourable water retention and movement, and porosity for better management for crop production.

Combined organic amendments and mineral fertilizer application increase rice yield by improving soil structure, P availability and root growth in saline-alkaline soil

In saline-alkaline soil, soil structural stability and phosphorus (P) availability are the limiting factors for crop yield. Organic amendments are proved to play a key role in soil quality, P availability and plant growth. A field experiment was carried out with different organic amendments level in the Yellow River Delta, five treatments were designed: (i) Control (no fertilization), (ii) NK (255 kg N ha−1 year−1 and 229 kg K ha−1 year−1), (iii) NPK (128 kg P2O5 ha−1 year−1 plus NK), (iv) NPKC1 (450 kg C ha−1 year−1 plus NPK) and (v) NPKC2 (900 kg C ha−1 year−1 plus NPK). The main results showed that: compared with NPK treatment, the mean weight diameter (MWD) of soil aggregates was increased by 33.8 % and 47.1 % in NPKC1 and NPKC2 treatments, respectively. And the percentage of water-stable aggregate (WSA) was also improved by 30.5 % and 40.16 % in NPKC1 and NPKC2 treatments, respectively. This was due to the increase of soil exchangeable Ca, soil organic carbon (SOC) and particulate organic carbon (POC) content, and the decrease in soil bulk density and exchangeable Na content, as well. Meanwhile, soil available P (AP), total P (TP), dicalcium P (Ca2-P) and octacalcium P (Ca8-P) contents were significantly increased with organic amendments addition. Based on the increase of soil structural stability and P availability, especially the accumulation of inorganic P (Pi) in soil macro-aggregates, root surface area and plant P use efficiency (PUE) were improved, which resulted in the grain yield increased by 12.2 % and 16.6 % in NPKC1 and NPKC2 treatments, respectively. Consequently, combined organic amendments and mineral fertilizer application were better in improving the soil structural stability, P availability and plant growth in saline-alkaline area.

黄土高原天然次生林植被演替过程中土壤团聚体有机碳动态变化

土壤团聚体物理保护是促进有机碳积累主要机制之一。以黄土高原子午岭林区天然次生林植被演替群落为对象，研究从农田、草地（白羊草，Bothriochloa ischaemum）、灌木林（沙棘，Hippophae rhamnoides）、先锋林（山杨，Populus davidiana）到顶级林（辽东栎，Quercus liaotungensis）5个植被演替阶段0-20 cm土壤团聚体稳定性和团聚体有机碳的动态变化，并分析团聚体有机碳的影响因素。结果表明：土壤团聚体稳定性随着植被演替显著提高（P<0.05），顶级林的团聚体稳定性最高；土壤有机碳含量和各粒径土壤团聚体（> 2 mm、2-0.25 mm、0.25-0.053 mm、<0.053 mm）有机碳含量均随着植被演替而增加。除草地0.25-0.053 mm团聚体有机碳含量最高外，其他演替阶段均为0.25-2 mm粒径最高。根系生物量、凋落物生物量、微生物生物量碳、团聚体稳定性均与团聚体有机碳含量呈显著正相关关系（P<0.05）。总体而言，长期植被演替有助于团聚体稳定性和团聚体有机碳累积。;Vegetation restoration plays an important role in soil structure and nutrients. The effects of vegetation restoration on the aggregate stability and soil carbon storage have been widely studied, but the distribution of aggregate associated organic carbon and the effects of plants on aggregate associated organic carbon in the secondary forest succession are still unclear. This paper studied the stability of soil aggregates and the changes of soil aggregate-associated organic carbon under the succession sequence of the secondary forests in Ziwuling forest region of the Loess Plateau, China. We discussed the dynamics of aggregate-associated organic carbon and its influencing factors following the secondary forest succession. In the field investigation, five vegetation succession stages were selected:farmland (CL), grassland (GL), shrub (S), pioneer forest (PF), and climax forest (CF). Soil samples in 0-20 cm were collected and the aggregates were separated by wet sieving. The stability of aggregates was characterized by mean weight diameter (MWD), geometric mean diameter (GMD), and percentage of water stable aggregates (WAS). The organic carbon, root biomass, litter biomass and microbial biomass carbon (MBC) of soil and aggregates were measured. The dynamics of soil aggregate-associated organic carbon and its influencing factors were analyzed. The results showed that soil organic carbon contents increased with vegetation succession, which showed that CF>PF>S>CL, and the organic carbon contents of aggregates increased more significantly from grassland to pioneer arbor stage. The succession of vegetation communities significantly increased the content of soil organic carbon. The stability of soil aggregate increased significantly with vegetation succession (P<0.05). The stability of soil aggregate in climax forest was the highest, and the contents of macroaggregate>0.25 mm in pioneer forest and climax forest were higher than that in farmland. The organic carbon contents of soil aggregates with different particle sizes increased with vegetation succession, and the organic carbon content of 2-0.25 mm was the highest in each succession stage. The stability of aggregates was positively correlated with the soil organic carbon. Root biomass, litter biomass and the MBC were significantly positively correlated with aggregate-associated organic carbon content. The main factors affecting soil organic carbon contents of aggregates were different in different particle sizes. Except the stages of vegetation succession, soil total organic carbon, litter biomass and soil aggregate stability were the main factors affecting the organic carbon content in the macroaggregates (> 0.25 mm), middle aggregates (0.25-0.053 mm), and microaggregates (<0.053 mm). The study suggests that vegetation succession plays an important role in the stability of aggregates and the fixation of organic carbon in aggregates.

Do roots bind soil? Comparing the physical and biological role of plant roots in fluvial streambank erosion: A mini-JET study

The roots of riparian vegetation can reduce fluvial streambank erosion by increasing soil resistance to erosion or by altering the applied hydrodynamic force of flowing water; however, the relative importance of these mechanisms is unknown. To assess the physical and biological effects of plant roots on streambank fluvial erosion, laboratory-scale testing was conducted using a mini Jet Erosion Testing (JET) device. Data analysis was conducted on three treatment groupings: (1) no roots (NR, n = 24); (2) synthetic roots (SR, n = 24); and (3) live roots (LR, switchgrass [Panicum virgatum], n = 12). Soil erosion was quantified by measuring the final volume of soil loss and calculating critical shear stress (τc) and the soil erodibility coefficient (kd). Potential explanatory soil and root properties, including percent water stable aggregates, root length density, and extracellular polymeric substances, were also measured. Kd was lower in rooted soil samples compared to NR when root length density was 2 cm cm−3 or higher, indicating that soil with densely packed fibers (either live and synthetic) have an impact on the applied hydrodynamic forces. However, τc was significantly higher in LR compared to both NR and SR, suggesting that only living roots provide additional soil protection by increasing soil resistance to fluvial erosion. The results of this study further emphasize that plant roots protect streambank soils from fluvial erosion through multiple mechanisms; nevertheless, further research is needed to determine which mechanism(s) plays a dominant role.

Existence of water repellency and its relation to structural stability of soils in a tropical Eucalyptus plantation forest

Water repellency is a globally well-known phenomenon in soils that is found to have direct or indirect impacts on vast majority of soil characteristics and dynamics. In this study, we aimed to examine the influence of soil water repellency on the structural stability of soils considering water stability of aggregates at the depths of 0–5, 5–10, 10–15, 15–20, and 20–25 cm. A Eucalyptus plantation forest characterized by steep slopes was selected for the study and the land was separated into three blocks (B1, B2, B3) considering the slope. The percentage of water stable aggregate (%WSA) was determined using a wet sieving apparatus. Water repellency in soils was examined using the water drop penetration time (WDPT) test and the sessile drop contact angle method. The water repellency and the organic matter content were highest in the topsoil (0–5 cm) and decreased with increasing soil depth showing strong negative exponential relationships. The clay content of B1 and B2 soils increased, and that of B3 decreased with increasing depth. The %WSA of the soils was very high showing >85% on the topsoil layer (0–5 cm), and >70% throughout the profile. Below 15 cm, B3 soils showed significantly higher water repellency compared with B1 and B2, however, showed no significant difference in %WSA compared with B1 and B2 soils. Although the primary cause of the reduction in the water repellency and %WSA with increasing soil depth seems to be the decrease in organic matter content, clay content can also be considered to have a pronounced influence. Despite the fact that the %WSA was very high on the surface, topsoil evidenced severe erosion corroborating that the improved stability of aggregate governed by water repellency does not necessarily lower the erosion. The %WSA might not be an effective indicator of the susceptibility to topsoil erosion in lands with steep slopes (>10°). Severe erosion in these sloped lands can be considered as resulted by the detachment of aggregates without disintegration, due to low cohesiveness and ease of detachment of aggregates as instigated by water-repellent conditions.

Soil organic carbon fractions and aggregation of a tropical Alfisol as affected by plant residues

Incorporation of plant residues into soil plays vital role in enhancing quality of fragile tropical soils. This study evaluated short-term effect of plant residues of different quality on organic carbon (OC) fractions, carbon management indices and stability of a sandy loam soil with low (&lt; 2%) initial OC content. The residues are Banana clippings (BC), Chromolaena odorata (CO), Leucaena leucocephala (LL), Maize Stover (MS), Neem clippings (NC), and Panicum maximum (PM) applied at 0 t ha-1 (control), 10 t ha-1 and 20 t ha-1 . These treatments were arranged in a randomized complete block design and replicated three times. Undisturbed soil samples were collected at 0-20 cm depth for determination of percent water stable aggregates (%WSA), aggregate ratio (AR) and Mean Weight Diameter (MWD). Pre-sieved (2 mm) soil samples from same depth were collected to determine structural index (SI), microaggregate stability, total OC (CT), labile OC (CL) and non-labile OC (CNL). Carbon indices, i.e. lability index (LI), carbon management index (CMI) and carbon pool index (CPI) were computed from the OC fractions to evaluate the best management practice. The OC fractions were significantly (p≤ 0.05) higher with LL applied at 20 t ha-1 (19.29 g kg-1 for CT, 1.20 g kg-1 for CL and 18.09 g kg-1 for CNL) than other treatments. This was followed by PM 10 t ha-1 , with 17.16 g kg-1 for CT and 16.44 g kg-1 for CNL. The LI (1.29) was highest with MS 10 t ha-1 , while CMI (166.6) and CPI (1.85) were highest with LL 10 t ha-1 and 20 t ha-1 respectively. Significant increase in %WSA of &gt; 0.25 mm size over &lt; 0.25 mm was observed with addition of residues which indicates binding of smaller aggregates into large fractions; while AR (11.97) was highest with CO 10 t ha-1 . Aggregate stability showed MWD (2.02 mm) was highest in soils treated with CO followed by PM (MWD = 1.86 mm) both at 20 t ha-1 ; but SI trend was higher with addition of LL and PM. Computed micro-aggregate stability indices were generally similar for all treatments. High positive correlations were obtained between MWD and CL (r = 0.634), LI (r = 0.686) and CMI (r = 0.641) with addition of Leucaena leucocephala. In conclusion, L. leucocephala, followed by P. maximum and C. odorata provided shortterm improvement in physical quality of this soil over other plant residues

Predicting soil aggregate stability using readily available soil properties and machine learning techniques

Aggregate stability is a measurement of soil quality, as the presence of stable aggregates relates to a wide range of soil ecosystem services. However, aggregates stability is not reported in most soil surveys, so predictive models have been focus of increasing attention as an alternative method in the absence of direct measurements. Therefore, the objective of this study was to develop a new model for predicting aggregate stability, using two machine learning techniques: An Artificial Neural Network (ANN) model and Generalized Linear Model (GLM). These techniques were applied to a soil dataset described in terms of soil texture, organic matter content, pH, and water-stable aggregates. This dataset included 109 soil samples obtained at 0–17 cm soil depth from hyperarid, arid, semiarid, and humid regions in Chile, including agricultural soils, shrubland, and forestland. Most soil textures in this dataset were sandy loam, loam, and clay loam, and each soil property had a large range of values. Aggregate stability was measured and computed as the percentage of water-stable aggregates using a wet sieving apparatus, and the ANN and GLM models were constructed and evaluated by repeated cross-validation (80% and 20% of dataset for training and testing, respectively). The ANN and GLM models were compared by computing the modified r2 (radj2), Root Mean Square Error (RMSE), and Mean Absolute Error (MAE). The results demonstrated a positive gradient of aggregate stability from arid (40% in average) to humid (87% in average) regions, which is related to the increase in organic matter content and decrease in pH. Organic matter content and pH exhibited a significant correlation to the aggregate stability, with r = 0.56 and r = −0.73, respectively. Moreover, among the fractions used to compute the soil texture, the clay content exhibited the highest correlation with aggregate stability (r = 0.30). These variables were used for training and testing the ANN and GLM models. The ANN model achieved superior performance in terms of the RMSE, radj2 and MAE in the cross-validation procedure, and showed r2 = 0.80 for training and r2 = 0.82 for testing. The GLM yielded r2 = 0.59 and r2 = 0.63 for training and testing, respectively. Therefore, despite the limitations observed when implementing ANN, its use is recommended instead of GLM as a reference model. Considering the small number of easily measured variables, this study provides two models that can be coupled with other existing soil routines or can be used directly to complete soil surveys where the aggregate stability was not measured.

Crop production kept stable and sustainable with the decrease of nitrogen rate in North China Plain: An economic and environmental assessment over 8 years

In pursuit of maximum grain yield farmers in the North China Plain usually apply excessive N fertilizer, resulting in wasted resources and environmental pollution. To assess the economic and environmental performances of different nitrogen rates will be conductive to sustain cleaner crop production. An 8-year field experiment was carried out with four treatments, N0 (0 kg ha−1 for winter wheat and summer maize), N1 (168 kg ha−1 for winter wheat and 129 kg ha−1 for summer maize), N2 (240 kg ha−1 for winter wheat and 185 kg ha−1 for summer maize) and N3 (300 kg ha−1 for winter wheat and summer maize), on the double cropping at Dawenkou research field (36°11’N, 117°06’E), Shandong Province, China. The crop production, soil physical-chemical parameters, and greenhouse gas emission are measured and the economic and environmental performances are assessed. The optimal nitrogen rate obtained the highest grain yield of summer maize in 4 of 8 year and was equivalent to conventional N rate in the other years. The nitrogen partial factor productivity and agronomic efficiency of optimal nitrogen rate was 63% and 58% higher than that of conventional nitrogen rate. The optimal nitrogen rate effectively decreased soil bulk density and increased weight percentage of water-stable aggregate and activities of urease and invertase compared to conventional nitrogen rate, which improved soil productivity. The fertilizer nitrogen loss and global warming potential of optimal nitrogen rate reduced by 76% and 35% compared to conventional nitrogen rate. The annual greenhouse gas intensity of optimal nitrogen rate decreased by 14–35% compared to others. The net ecosystem economic budget under optimal nitrogen rate is 252–604 $ ha−1 yr.−1 higher than other addition levels. The optimal nitrogen rate produces more grains and obtains higher economic and environmental benefits.

Increasing Temperature and Microplastic Fibers Jointly Influence Soil Aggregation by Saprobic Fungi.

Microplastic pollution and increasing temperature have potential to influence soil quality; yet little is known about their effects on soil aggregation, a key determinant of soil quality. Given the importance of fungi for soil aggregation, we investigated the impacts of increasing temperature and microplastic fibers on aggregation by carrying out a soil incubation experiment in which we inoculated soil individually with 5 specific strains of soil saprobic fungi. Our treatments were temperature (ambient temperature of 25°C or temperature increased by 3°C, abruptly versus gradually) and microplastic fibers (control and 0.4% w/w). We evaluated the percentage of water stable aggregates (WSA) and hydrolysis of fluorescein diacetate (FDA) as an indicator of fungal biomass. Microplastic fiber addition was the main factor influencing the WSA, decreasing the percentage of WSA except in soil incubated with strain RLCS 01, and mitigated the effects of temperature or even caused more pronounced decrease in WSA under increasing temperature. We also observed clear differences between temperature change patterns. Our study shows that the interactive effects of warming and microplastic fibers are important to consider when evaluating effects of global change on soil aggregation and potentially other soil processes.

Effects of arbuscular mycorrhizal fungi on inoculated seedling growth and rhizosphere soil aggregates

Arbuscular mycorrhizal fungi (AMF) inoculation have been shown to enhance host plant growth and rhizosphere soil aggregates largely due to the combined effect of extraradical hyphae and glomalin-related soil proteins but their effects on rocky desertified soils remain unknown. Extensive karst area of southwest China has undergone rocky desertification because of soil erosion and vegetation degradation. Karst soils in this area are mainly composed of silty clay loam developed from carbonate rock erosion under subtropical humid monsoon climate. We tested the hypothesis that AMF colonization of tree seedlings would improve water stable aggregates of degraded karst soil and enhance seedling growth. Seedlings of two tree species, Toona sinensis and Delavaya toxocarpa suitable for afforestation in karst area, were inoculated separately with three AMF, Funneliformis mosseae, Glomus versiforme and Rhizophagus intraradices in pots containing rocky desertified soil. Non-inoculated seedlings were used as control. After 12 months we found that the percentage of water stable aggregates (diameter >0.25 mm; WSA>0.25) in the rhizosphere soil of the inoculated seedlings was increased by 15.6–20.5% compared to control. AMF colonization significantly increased the quantity of aggregates with diameter > 2 mm compared to control but soil aggregates of size class 0.25 – 0.5 mm decreased significantly in inoculated seedlings, regardless of tree species. Shoot biomass of inoculated T. sinensis and D. toxocarpa seedling was increased by 15.7–21.2% and 8.5–20.4%, respectively compared to non-inoculated seedlings. In contrast, AMF inoculation minimally influenced the root biomass of the two tree species. The easily extractable glomalin (EEG) content and mean weight diameter (MWD) of rhizospheric soil of the inoculated seedlings increased by 28.9–75.1% and 31.7–48.1%, respectively compared to control. The AMF colonization was highly correlated with WSA>0.25, EEG and MWD. Overall results support our hypothesis that AMF colonization enhance the quantity of rhizospheric soil aggregates and improve the growth of host seedlings. We conclude that planting tree species inoculated with AMF has a potential for restoration of degraded karst ecosystem. In future research other locally adapted tree and shrub species should be tested following AMF inoculation to prepare a wider planting stocks to be used in restoration of degraded karsts.

Conservation agriculture effects on soil properties and crop productivity in a semiarid region of India

Conservation agriculture (CA) including reduced or no-tillage and crop residue retention, is known to be a self–sustainable system as well as an alternative to residue burning. The present study evaluated the effect of reduced tillage coupled with residue retention under different cropping systems on soil properties and crop yields in a Vertisol of a semiarid region of central India. Two tillage systems – conventional tillage (CT) with residue removed, and reduced tillage (RT) with residue retained – and six major cropping systems of this region were examined after 3 years of experimentation. Results demonstrated that soil moisture content, mean weight diameter, percent water stable aggregates (&amp;gt;0.25mm) for the 0–15cm soil layer were significantly (P&amp;lt;0.05) affected by tillage practices. Soil penetration resistance was significantly higher for RT than CT. Irrespective of soil depth, there was higher soil organic carbon (SOC) for RT than CT. The SOC fractions followed in the order: non-labile&amp;gt;moderately labile&amp;gt;less labile. At the 0–15cm depth, the contributions of moderately labile, less labile and non-labile C fractions to total organic C were 39.3%, 10.3% and 50.4% respectively in RT and corresponding values for CT were 38.9%, 11.7% and 49.4%. Significant differences in different C fractions were observed between RT and CT. Soil microbial biomass C concentration was significantly higher in RT than CT at 0–15cm depth. The maize–chickpea cropping system had significantly (P&amp;lt;0.05) higher soybean grain equivalent yield of 4.65 t ha–1 followed by soybean+pigeon pea (2:1) intercropping (3.50 t ha–1) and soybean–wheat cropping systems (2.97 t ha–1). Thus, CA practices could be sustainable management practices for improving soil health and crop yields of rainfed Vertisols in these semiarid regions.

Corrigendum to: Conservation agriculture effects on soil properties and crop productivity in a semiarid region of India

Conservation agriculture (CA) including reduced or no-tillage and crop residue retention, is known to be a self–sustainable system as well as an alternative to residue burning. The present study evaluated the effect of reduced tillage coupled with residue retention under different cropping systems on soil properties and crop yields in a Vertisol of a semiarid region of central India. Two tillage systems – conventional tillage (CT) with residue removed, and reduced tillage (RT) with residue retained – and six major cropping systems of this region were examined after 3 years of experimentation. Results demonstrated that soil moisture content, mean weight diameter, percent water stable aggregates (&amp;gt;0.25mm) for the 0–15cm soil layer were significantly (Pmoderately labile&amp;gt;less labile. At the 0–15cm depth, the contributions of moderately labile, less labile and non-labile C fractions to total organic C were 39.3%, 10.3% and 50.4% respectively in RT and corresponding values for CT were 38.9%, 11.7% and 49.4%. Significant differences in different C fractions were observed between RT and CT. Soil microbial biomass C concentration was significantly higher in RT than CT at 0–15cm depth. The maize–chickpea cropping system had significantly (P–1 followed by soybean+pigeon pea (2:1) intercropping (3.50 t ha–1) and soybean–wheat cropping systems (2.97 t ha–1). Thus, CA practices could be sustainable management practices for improving soil health and crop yields of rainfed Vertisols in these semiarid regions.

Effect of inorganic fertilisers and organic amendments on soil aggregation and biochemical characteristics in a weathered tropical soil

Highly weathered laterite soils are a characteristic feature of humid tropics with undulating topography and high rainfall. The crop of cashew (Anacardium occidentale L.) has been cultivated in such landscapes, mainly to prevent further degradation due to the drought hardiness of cashew and requirement of very limited soil disturbances for its cultivation. Providing proper nutrient management is important for balancing the nutrient removal by tree crops especially in poor fertile soils. A study was initiated, after 5 years of application of inorganic fertilisers and organic amendments to cashew in a weathered tropical soil, to evaluate the effects of organic and inorganic sources of nutrients on soil aggregation and biochemical characteristics. The experiment consisted of 11 treatments as Farm Yard Manure (FYM) alone; FYM + biofertiliser consortia; FYM, rock phosphate and wood ash; poultry manure; In situ composting using recyclable cashew biomass and weeds; In situ composting using recyclable cashew biomass and weeds + green manuring; vermicomposting of recyclable cashew biomass; FYM + organic cakes + recyclable cashew biomass + biofertiliser consortia; recommended dose of nitrogen, phosphorus and potassium fertiliser (NPK fertiliser); recommended NPK fertiliser + FYM; and control without nutrient application. Soil samples were collected from surface 0–30 cm layer. The soil samples were fractionated into three aggregate sizes, i.e., >2 mm (large macroaggregates), 0.25–2 mm (small macroaggregates), 0.053 to 0.25 mm (microaggregates) and <0.053 mm (silt + clay size fraction) using wet sieving. The results indicated that the organic sources of nutrient application increased the proportion of large and small macroaggregates. The treatments receiving only inorganic nutrients and no nutrients contained significantly higher silt + clay fractions (47.7 and 45.5% respectively). A higher percentage of water stable aggregates (47.4–70.7%) and increased aggregate stability (mean weight diameter) (0.78–1.26 mm) was recorded with the application of organic sources of nutrients. Aggregates in the silt + clay size faction and microaggregates recorded significantly higher carbon compared to small and large macroaggregates. Compared to control, the application of different organic amendments increased the soil organic matter (SOM) by 2.2–12.7% in silt + clay size fraction; 14.6–37.0% in microaggregates; 18.4–51.7% in small macroaggregates and 17.7–50.9% in large macroaggregates. Our findings reinforce that the annual application of manures and amendments to weathered tropical soil is important to improve biological properties of soil in terms of soil enzyme activities, microbial carbon and nitrogen, and to prevent further degradation of soil under such fragile environment.

Impact of monovalent cations on soil structure. Part I. Results of an Iranian soil

AbstractThis study investigated the impact of monovalent cations on clay dispersion, aggregate stability, soil pore size distribution, and saturated hydraulic conductivity on agricultural soil in Iran. The soil was incubated with treatment solutions containing different concentrations (0-54.4 mmol l−1) of potassium and sodium cations. The treatment solutions included two levels of electrical conductivity (EC=3 or 6 dS m−1) and six K:Na ratios per electrical conductivity level. At both electrical conductivity levels, spontaneously dispersible clay increased with increasing K concentration, and with increasing K:Na ratio. A negative linear relationship between percentage of water-stable aggregates and spontaneously dispersible clay was observed. Clay dispersion generally reduced the mean pore size, presumably due to clogging of pores, resulting in increased water retention. At both electrical conductivity levels, hydraulic conductivity increased with increasing exchangeable potassium percentage at low exchangeable potassium percentage values, but decreased with further increases in exchangeable potassium percentage at higher exchangeable potassium percentage. This is in agreement with earlier studies, but seems in conflict with our data showing increasing spontaneously dispersible clay with increasing exchangeable potassium percentage. Our findings show that clay dispersion increased with increasing K concentration and increasing K:Na ratio, demonstrating that K can have negative impacts on soil structure.

Physicochemical and microbial soil quality indicators as affected by the agricultural management system in strawberry cultivation using straw or black polyethylene mulching

The aim of this study was to understand the differences in physicochemical and microbial soil quality resulting from the use of either wheat straw or black polyethylene, two widely used practices in strawberry cultivation. Soil samples were collected from strawberry crops used during 4 years as mono-cropping system, covered by either straw or black polyethylene (plastic mulching). Soil physicochemical properties included water content, pH, effective cation exchange capacity, elemental analysis of total carbon and nitrogen, dissolved and total organic carbon, and soil stability by percentage of water-stable aggregates (>0.2mm). Soil microbial analysis comprised soil microbial biomass (Cmic and Nmic and DNA concentrations) and estimation of soil eco-physiological conditions Cmic:Corg and Nmic:Ntot. Soil bacteria and a fraction of cultivable fungi were studied respectively by molecular analysis and counting of colony-forming units (CFU values). Mycotoxin concentration in soil (deoxynivalenol) was used as an indirect indicator of fungal stress. The plastic mulching system showed positive effects on soil physicochemical properties as compared to straw mulching: Higher soil carbon content and better aggregate stability were observed in soils under plastic film, and the values for soil microbial biomass were comparable in both systems. Yet, soil eco-physiological conditions under plastic mulching were less appropriate compared to straw, as reflected by a reduced Cmic:Corg ratio (1.3±0.3%), followed by a decline of the number of bacteria (18%), a six-fold reduction of the biomass of soil cultivable fungi, and finally by a two-times higher deoxynivalenol concentration in soil (mean 2.2±2.4μgkg−1). This indicates that the plastic mulching system led to less favourable soil conditions and that the production of mycotoxins can be understood as a stress induced response by fungi. Further information is therefore needed to assess how the quality of soil is restricted by the shift of soil microbial communities and by the production of mycotoxins, especially in intensive agriculture with long-term plastic coverage.

INFLUENCE OF SOME PROPERTIES CONCERNING WATER STABLE AGGREGATES OF SALINE SOILS

According to literature, aggregate stability of soils is influenced by: particle size and soil texture, soil structure, content of Ca2+ and Mg2+, mineral clay type, soil content of organic matter, soil processing degree. This paper aims to investigate the influence of some physical, microbiological and chemical properties of saline soil concerning water-stable aggregate. The hydro system stability of the aggregates appears in the specialized studies as having a positive correlation with microorganisms activity and thus with their behaviour in the soil. Our data support this theory, since according to our research there is a positive correlation between the percentage of stable aggregates and the amount of microorganisms. In samples from cultivated soil (noted in this paper by S), where the amount of microorganisms is higher, the percentage of water-stable aggregate is higher as well. In samples from uncultivated soil (noted in this paper by M), where the amount of microorganisms is lower, the percentage of water-stable aggregate is lower too. According to research studies and to the specialty literature, sodium is an element with a disruptive role on the stability of the aggregates. Our experimental data has shown that in samples from uncultivated soil (M), where sodium values are much higher, compared to samples from the cultivated soil (S), the percentage of water-stable aggregate is lower than the percentage of water-stable aggregate in the samples from the cultivated soil. Also, our results concerning porosity values ranging between 42.27% (the minimal value) to 49.86% the maximal value, show that these soils can be characterized as having low and very low porosity according to specialized literature. However, it must be taken into account the fact that in clay soils the porosity is very variable, depending on how the soil contracts, swells, disperses, compacts or cracks. In addition, the values describing the water permeability of the soil show that this characteristic for the control soil is small, the permeability coefficient k having values between 1.73 10-8 -7.19 10-8. For the cultivated soil, the permeability is medium, k having values between 4.97 10-7 - 7.83 10-8. Our data regarding soil physical properties, as well as the data about soil chemical properties that have been analyzed in this study show a weak quality of these soils, which cannot sustain a healthy crop with good economic yield.

Aggregate stability and size distribution of red soils under different land uses integrally regulated by soil organic matter, and iron and aluminum oxides

The stability and size distribution of soil aggregates is profoundly affected by land use, but the influencing mechanisms of land use are not clear. A study was carried out to investigate and attempted to interpret the effects of land use on soil aggregates from types of land use and soil properties in soil samples and size fractions of soil aggregates. Soil samples were taken from 9 sites under paddy, forest, and upland in southern China. The wet-sieving method was used to obtain 6 size fractions of soil aggregates: >5, 5–2, 2–1, 1–0.5, 0.5–0.25, and <0.25mm. The stability and size distribution of soil aggregates was measured as mean weight diameter (MWD), the percentage of water-stable aggregate (WSA) and the percentage of each size fraction (PSA). The quantities of soil organic carbon (SOC), humic substances, dithionite-citrate-bicarbonate (DCB) and oxalate extractable iron (Fe) and aluminum (Al) oxides were also measured. The results showed that types of land use solely explained 66.6% variation of soil aggregates; SOC, DCB-extractable Fe and Al oxides, and oxalate-extractable Al oxide caused 84.3% variation, in which SOC contributed 29.0%, Fe and Al oxides contributed 33.8%, and their interactions contributed 21.4%. The multiple linear regression and partial correlation analysis showed that soil organic matter and Fe and Al oxides had significant effects but played different roles on the stability and size distribution of soil aggregates. The study suggests that land use affects the stability and size distribution of soil aggregates through the integration of soil organic matter and Fe and Al oxides.