Continental Patterns of Electrical Conductivity and Soil Aggregates in European Wheat Agroecosystems

Organic manure is beneficial for macro-aggregate formation and soil organic carbon (SOC), but how SOC change in aggregate fractions in time-series is still uncertain. Moreover, greenhouse systems converted from cereal fields quickly faced soil degradation. Thus, the role of organic manure here should be discussed. The main objectives of this study were to determine the change of SOC fractions in bulk soil and aggregation level affected by long-term organic manure application. Using 13C solid-state nuclear magnetic resonance (NMR) spectroscopy, we investigated the SOC and its fraction changes within bulk soil and aggregate fractions under 1-year, 9-year, and 14-year organic greenhouse vegetable cultivation, and we also analysed the soil properties of rice-wheat rotation (RWR) fields as the control. Soil aggregate samples were wet sieved into large macro-aggregates (> 2 mm), small macro-aggregates (2–0.25 mm), micro-aggregates (0.053–0.25 mm), and silt and clay particles (<0.053 mm). The proportion of large macro-aggregates increased significantly (P ≤ 0.05) from 1.68 to 7.76% during the 14-year organic cultivation period. Similar trends could also be found in SOC and its fractions. Specifically, the O-alkyl C increased fastest by 14.5 g kg−1 over these years, but its proportion decreased. The change in aggregate associated C was concentrated on large macro-aggregates and micro-aggregates. Pearson’s correlation suggested that there was a non-significant relation between SOC and soil aggregation, while the soil aggregate associated C had a significantly positive relationship with SOC and its fraction amounts. However, the proportion of O-alkyl C was less; the aggregation associated C was higher. This study has shown the different effects of SOC fractions on soil aggregation and aggregate associated C in organic greenhouse vegetable fields. The stable C fractions might show contribution in soil aggregate associated C than active C fractions. It might improve our knowledge about how organic manure may influence soil aggregation by increasing SOC after a long-term greenhouse vegetable plantation.

Soil pH and electrical conductivity (EC) are two major chemical properties affecting nutrient availability and rice grain yield. Therefore, this study was conducted to investigate the variation of pH and EC in the topsoil layer (0-15 cm) of rice fields as affected by major water source used for rice cultivation, rice-based cropping system adopted and rice growing soil orders in different agro-climatic zones (ACZs) in Sri Lanka. A total of 998 soil samples were collected from lowland rice fields. Both pH and EC were measured in 1:5 soil: water extracts. The pH of soil samples was in the range of 3.0-7.7 with a mean value of 5.0. Moreover, 75% of the soil samples had pH values below the optimum range for rice cultivation (5.5-7.0). Values of pH observed in Dry Zone soils were higher (5.2) than those in Wet Zone (4.4). Soil EC values ranged between 1.0 - 3,100 μScm−1 with a mean value of 148.5 μScm−1. Soil EC was similar among climatic zones (P&gt;0.05). Upcountry Intermediate zone recorded the highest soil EC than that in other ACZs (P&lt;0.05). Moreover, 73%, 22%, 3%, 2% and 0.1% of soil samples recorded EC values in the ranges of less than 150 (non-saline), 150-400 (slightly saline), 400-800 (moderately saline), 800-2000 (highly saline) and more than 2000 (very highly saline) μScm−1, respectively. Considering micro (e.g. paddy track) and macro (e.g. ACZ) scale spatial heterogeneity in soil pH and EC, appropriate site-specific strategies need to be adopted to improve soil pH and EC to suit sustainable rice crop production.

The long-term use of fertilizers and pesticides in conventional cultivation has resulted in a decrease in soil productivity and vegetable yields in greenhouses. However, there is little research exploring the changes in soil organic carbon and the microbial community mediated by soil aggregates, or their impacts on soil productivity. This study investigated the properties of soil aggregates, including the levels of organic carbon fractions, microbial community, and enzyme activity with the three aggregate classes: microaggregates (&lt;0.25 mm), small macroaggregates (2–0.25 mm) and large macroaggregates (&gt;2 mm) under conventional cultivation (CC), integrated cultivation (IC), and organic cultivation (OC) in greenhouses. The results showed that (1) OC and IC promoted the formation of small macroaggregates and enhanced aggregate stability compared to CC; (2) SOC in the three size fractions of OC increased by 92.06–98.99% compared to CC; EOC increased by 98.47–117.59%; POC increased by 138.59–208.70%; MBC increased by 104.71–230.61%; and DOC increased by 21.93–40.90%, respectively; (3) organic cultivation significantly increased enzyme activity in all three particle-size aggregates and increased the relative abundance of bacteria in microaggregates as well as the relative abundance of fungi in small macroaggregates. Structural equation model (SEM) analysis revealed that organic farming practices fostered the development of smaller macroaggregates, elevated microbial and enzyme activities within soil aggregates, and facilitated the conversion of soil nutrients and carbon sequestration. Therefore, long-term organic cultivation increases soil carbon content and vegetable yield in greenhouses by increasing the proportion of small aggregates. In conclusion, long-term organic cultivation in greenhouses improves soil structure, increase soil fertility and vegetable yield, and has a positive impact on the environment. Organic cultivation increases soil fertility and contributes to maintaining ecological balance and protecting the environment in greenhouses.

We discussed two methods to calculate displacement ratio of the soil tilled by rotary tillage in our first report. The present report is concerned with the results of application for the estimation of displacement ratio of the soil tilled by down-cut and up-cut rotary tillages. This paper also deals with the distribution of electrical conductivity on the soils in various upland fields.The results are as follows.1) The electrical conductivity of soil at the upland fields under the natural condition showed the value of 74.6-399.0μS/cm and the each field differed remarkably in electrical conductivity. This result was caused by the remaining rate of electolyte produced by chemical fertilizer.2) From the comparison of electrical conductivity before tillage with one after tillage, the soil displacement in the backward and forward by rotary tillage was confirmed.3) The large variation of displace-ment ratio of the tilled soil was observed between mesuring points [b2-b4 points to stabilize originally] in up-cut rotary experiment. The variation was also remarkably larger than one of down-cut rotary tillage, because of the variation of electrical conductivity of soil mixing KCI.4) In case of the method by conditional inequality, the ratio of soil displacement is calculated with a certain range. According to the results of this experiment, its range was the value within ±1.1%. This degree of ranges are practically negligible.5) The difference of soil displace-ment ratio between the method by simultaneous equations of three unknowns and conditional inequa-lity was 0.5% at the most except one case. Therefore, we think that validity of the both methods was proved.6) Synthesizing the various experiment results of this parper, the electrical conductivity method used the mixture soil of KCI is effective as method to estimate the displacement ratio of soil tilled by rotary tillage.

PURPOSE: Soil organic carbon (SOC) content and stability, which are regulated by microbial communities, vary depending on aggregate size. The objectives of this study were to investigate the distribution of the SOC fraction and microbial community composition within soil aggregates when subjected to different fertilization treatments. MATERIALS AND METHODS: This study used high-throughput sequencing technology to analyze the soil microbial community distribution in different-sized aggregate fractions [> 2 mm (large macro-aggregates), 2–0.25 mm (small macro-aggregates), and < 0.25 mm (microaggregates)] when they were subjected to different fertilization treatments in a 16-year greenhouse experiment. The three treatments were chemical fertilizer (CF), 50% organic fertilizer + 50% chemical fertilizer (MF), and organic fertilizer (OF). RESULTS AND DISCUSSION: The results showed that the application of organic fertilizer significantly increased the soil organic carbon (SOC), dissolvable organic carbon (DOC), and microbial biomass carbon (MBC) contents and changed microbial community composition in all the different-sized soil aggregates. We observed that OF significantly reduced the relative abundance of bacterial communities in all aggregates and significantly increased the relative abundances of fungal communities in small macro-aggregates. The larger fungal communities in small macro-aggregates could promote soil aggregation and C sequestration. CONCLUSIONS: Organic fertilization increased the substrate contents in soil aggregates and enhanced soil aggregation and microbial activity in macro-aggregates, which are critical factors that facilitate C transformation and sequestration. These improvements resulted in significantly improved soil fertility and increased vegetable yield in the greenhouses.

Organic farming, which is growing in popularity, has been proposed as a sustainable alternative to conventional farming practices. However, it is not known how organic farming systems affect soil erosion risk and sediment-bound nutrient transport. Our objectives were to compare soil erosion risk and sediment bound nutrient transport potential for grain-based conventional and organic cropping systems by determining selected soil physical properties and distributions of carbon (C), nitrogen (N), and phosphorus (P) in soil aggregates of the 0-5 cm depth of a Christiana-Matapeake-Keyport soil association. We measured soil bulk density, aggregate stability, aggregate size distributions, and total C, N, and P associated with five soil aggregate size classes in no-till (NT) and chisel till (CT) systems and in an organic system (ORG). No-till soils had lesser bulk density and greater aggregate stability than did CT and ORG soils. Carbon, N, and P concentrations were greater in large (g2.00 mm) and small macroaggregates (0.21 to 2.00 mm) than in microaggregates (l0.21 mm) regardless of cropping system. When nutrient concentrations were combined with aggregate distribution data, the quantity of aggregate associated nutrients was greatest in microaggregates in ORG and CT soils but greatest in macroaggregates in NT soils. These results indicate an increased risk of sediment associated nutrient transport from ORG and CT soils compared with NT soils, since microaggregates in these soils are preferentially lost through sediment transport. The NT cropping system promoted macroaggregate formation and reduced the risk of particulate nutrient transport in this warm, humid region soil.

Brazilian Atlantic Forest hotspots play an important role in global carbon stock and sequestration. Despite this biome is currently under progressive degradation with direct impacts on soils, little information is available on the dynamics of SOC within aggregates under different land uses in patches of this Atlantic Forest hotspot in Brazilian semi-arid. Three typical land uses (woodland, agroforestry system (AFS), and pasture) and different soil layers (0.0–0.2 and 0.2–0.4 m) were evaluated in the humid highlands of northeastern Brazil. Soil aggregate stability and the OC stock and iron oxides (Fed) in large macroaggregates (LA: > 2 mm), small macroaggregates (SA: 0.25–2 mm), and microaggregates (MA: 0.25–0.053 mm) were evaluated. Land use affects soil aggregation and distribution of size fractions by altering aggregate-associated OC. OC content was significantly higher in large macroaggregates of woodland and the agroforestry system. Large and macroaggregates-associated OC stocks had a dominant effect on aggregate-associated OC stocks in woodland and the agroforestry system, respectively. The OC stock in the bulk soil of AFS is directly related to the proportions and microaggregate-associated OC stock. Iron oxides also strongly influence the formation of large macroaggregates and microaggregates in the agroforestry system. Thus, AFS stabilizes soil carbon in small macroaggregates and microaggregates (associations with soil minerals), constituting an important aspect of carbon cycling in fragile patches of humid Atlantic Forest in Brazilian semi-arid.

The influence of biochar on the soil structure and aggregate stability has been debated in previous studies. To probe the action of biochar on soil aggregates, a 5-year field experiment was implemented in the brown earth soil of northeastern China. We determined the aggregate distribution (> 2000μm, 250-2000μm, 53-250μm, and < 53μm) and organic carbon (OC) and organo-mineral complex contents both in the topsoil (0-20cm) and within the soil aggregates. Three treatments were studied as follows: control (basal application of mineral NPK fertilizer), biochar (biochar applied at a rate of 2.625tha-1), and stover (maize stover applied at a rate of 7.5tha-1), and all treatments received the same fertilization. The biochar and stover applications decreased the soil bulk and particle densities significantly (p < 0.05) and enhanced the soil total porosity. Both amendments significantly (p < 0.05) enhanced the total OC, heavy OC fractions, and organo-mineral complex quantities in the bulk soil as well as in all the studied aggregate fractions. Biochar and stover applications promoted the formation of small macroaggregates. A greater amount of organic matter was contained in the macroaggregates, which led to the formation of more organo-mineral complexes, thereby improving soil aggregate stability. However, the different mechanisms underlying the effect of biochar and stover on organo-mineral complexes need further research. Biochar and stover applications are both effective methods of improving the soil structure in Northeast China.

A farm's soil moisture and soil electrical conductivity (EC)readings are extremely valuable for a farmer. They can help her reduce water use and improve productivity. However, the high cost of commercial soil moisture sensors and the inaccuracy of sub-1000 dollar EC sensors have limited their adoption. In this paper, we present the design and implementation of a system, called Strobe, that senses soil moisture and soil EC using RF propagation in existing Wi-Fi bands. Strobe overcomes the key challenge of limited bandwidth availability in the 2.4 GHz unlicensed spectrum using a novel multi-antenna technique. It maps the propagation time and amplitude of Wi-Fi signals received by different antennas to the soil permittivity and EC, which in turn depend on soil moisture and salinity. Our experiments with USRP, WARP, and commodity Wi-Fi cards show that Strobe can accurately estimate soil moisture and EC using Wi-Fi, thereby showing the potential of a future where a farmer can sense soil in their farm without investing 1000s of dollars in sensing tools.

Effects of tillage and residue managements on organic C accumulation and soil aggregation in a sandy loam soil of the North China Plain

The accurate monitoring of soil salinization plays a key role in the ecological security and sustainable agricultural development of semiarid regions. The objective of this study was to achieve the best estimation of electrical conductivity variables from salt-affected soils in a south Mediterranean region using Sentinel-2 multispectral imagery. In order to realize this goal, a test was carried out using electrical conductivity (EC) data collected in central Tunisia. Soil electrical conductivity and leaf electrical conductivity were measured in an olive orchard over two growing seasons and under three irrigation treatments. Firstly, selected spectral salinity, chlorophyll, water, and vegetation indices were tested over the experimental area to estimate both soil and leaf EC using Sentinel-2 imagery on the Google Earth Engine platform. Subsequently, estimation models of soil and leaf EC were calibrated by employing machine learning (ML) techniques using 12 spectral bands of Sentinel-2 images. The prediction accuracy of the EC estimation was assessed by using k-fold cross-validation and computing statistical metrics. The results of the study revealed that machine learning algorithms, together with multispectral data, could advance the mapping and monitoring of soil and leaf electrical conductivity.

Smooth vetch covering alters soil aggregate microbial metabolic limitations in citrus orchards

The soil-overturning properties is an important matter in the working results by rotary tillage, but the mesuring method is not still established in Japan. The purpose of this study is to obtain establishment of the mesuring method and the accurate ratio of soil displacement by rotary tillage. This paper deals with two methods calcurating the ratio of soil displacement.In this experiment, we adopted the method to use the soil mixed kalium chloride (KCI), as electrical conductivity and concentration of solution of KCI were in proportion to each other. After the electrical conductivity of the soil which mixed two level's soils differing in electrical conductivity was mesured, we discussed on a hypothetical equation to calculate the electrical conductivity of the mixed soils. The deviation between mesured electrical conductivity and calculated one showed the range of -3.4-2.3%. However it is assumed that this degree of errors are practically admitted.From application of the hypothetical equation, the two methods (simultaneous equations of three unknowns and conditional inequality) to obtain the ratio of soil displacement were derived. Mesuring the electrical conductivity of soils which were picked before and after rotary tillage, we can easily estimate by these methods the each ratio that a soil layer before tillage moved to the three layers after tillage.The method by simultaneous equations of three unknowns must perform the experiment of three plots in which the mixture soil of KCI was put at each layer before rotary tillage. Moreover, this method needs to make the uniform conditions of the three experimental plots.In case of the method by conditional inequality, the ratio of soil displacement is calculated with a certain range. Therefore if this range increases, the estimating inequality become useless. However, increasing the electrical conductivity of mixture soil of KCI, it is possible to decrease the range within 1%.

To clarify the nutrient characteristics of 'salt island' and 'fertile island' effects in saline-alkali soil, the native Tamarix chinensis of the Yellow River Delta (YRD) was selected to measure its soil pH,electrical conductivity (EC), organic carbon (SOC),total nitrogen (N),total phosphorus (P) and their stoichiometry characteristics at different soil depths. The results showed that soil pH and EC increased with the increasing soil depth. Soil EC and P in the 0-20 cm layer decreased and increased from canopied area to interspace,respectively. SOC,N,N/P and C/P in the 20-40 cm soil layer decreased, and C/N increased from the shrub center to interspace. SOC and N contents between island and interspace both decreased but P content decreased firstly and then increased with the increasing soil depth. Soil pH correlated positively with EC. In addition, pH and EC correlated negatively with C,N,P contents and their ecological stoichiometry.

Winter climate change has great potential to affect the functioning of terrestrial ecosystems. In particular, increased soil frost associated with reduced insulating snow cover may impact the soil nitrogen (N) dynamics in cold ecosystems, but little is known about the variability of these effects among the soil aggregates. A snow manipulation experiment was conducted to investigate the effects of snow absence on N cycling within soil aggregates in a spruce forest on the eastern Tibetan Plateau of China. The extractable soil available N (ammonium and nitrate), net N mineralization rate, and N cycling-related enzyme activities (urease, nitrate reductase, and nitrite reductase) were measured in large macroaggregate (>2 mm), small macroaggregate (0.25–2 mm), and microaggregate (<0.25 mm) during the early thawing period in the years of 2016 and 2017. Snow absence increased soil N availabilities and nitrite reductase activity in microaggregate, but did not affect net N mineralization rate, urease or nitrate reductase activities in any of the aggregate fractions. Regardless of snow manipulations, both soil inorganic N and nitrate reductase were higher in small macroaggregate than in the other two fractions. The effect of aggregate size and sampling year was significant on soil mineral N, net N mineralization rate, and nitrite reductase activity. Our results indicated that snow cover change exerts the largest impact on soil N cycling within microaggregate, and its effect is dependent on winter conditions (e.g., snow cover and temperature). Such findings have important implications for soil N cycling in snow-covered subalpine forests experiencing pronounced winter climate change.