A New Soil Sampling Design in Coastal Saline Region Using EM38 and VQT Method

Spatial sampling design based on the variability and distribution of soil properties is an important issue with the progress in precision agriculture and soil ecology. Electromagnetic induction (type EM38) and variance quad-tree (VQT) method were both applied to optimize the sampling scheme of soil salinity in a coastal reclamation field in north Jiangsu Province, China. Apparent soil electrical conductivity (ECa) measured with EM38 was used as an ancillary variable and the spatial distribution of ECa was used as priori information. The process and result of VQT algorithm analysis was illustrated and the obtained sampling strategy was validated using observed soil salinity. Then the spatial precision and sampling efficiency were evaluated. The result indicated that the spatial distribution of soil salinity produced with the VQT scheme was quite similar to that produced with total sampling sites, while sampling quantity of the former was reduced to approximately 1/2 of the latter. The spatial precision of VQT scheme was considerably higher than that of traditional grid method with respect to the same sampling number, and fewer samples were required for VQT scheme to obtain the same precision level. A 17.3% increase in sampling efficiency was achieved by VQT over grid method at the precision level of 90%. The VQT method was proved to be more efficient and economical because it can sample intensively or sparsely according to variation status in local areas. The associated application of EM38 and VQT method provides efficient tools and theoretical basis for saving sampling cost and improving sampling efficiency in coastal saline region and enriching soil ecology

Quantitative evaluation of soil salinity and its spatial distribution using electromagnetic induction method

In the Lower Yellow River Delta, soil salinity is a problem due to the presence of a shallow, saline water table and marine sediments. Spatial information on soil salinity at the field level is increasingly needed, particularly for better soil management and crop allocation in this area. In this paper, a mobile electromagnetic induction (EMI) system including EM38 and EM31 is employed to perform field electromagnetic (EM) survey, and fast determination and quantitative evaluation of the spatial pattern of soil salinity is discussed using the field EM survey data. Optimal operation modes of EM38 and EM31 are determined to establish multiple linear regression models for estimating salinity from apparent soil electrical conductivity (ECa). Spatial trend and semivariogram are illustrated and spatial distribution of field salinity status is further visualized and quantitatified. The results suggest that ECa (EM38 and EM31) data is highly correlated with salinity, and that the interpretation precision of soil salinity at various layers can be improved using EM38h and EM31h (where h represents the horizontal mode of EM measurement). Both EM38h and EM31h exhibit significant geographic trend. Nested spherical models fit the semivariance of EM38h and EM31h better than single spherical models. Spatial autocorrelation of EM31h is stronger than that of EM38h, and short-range variation is the chief constitute of spatial heterogeneity for both EM38h and EM31h. Quantitative classification shows that soil salinity exhibits the trend of accumulation in the root zone. In 0-1.0 m solum, heavy salinized and saline soils are the predominant soil types, accounting for 54% and 41% of total survey area, respectively. The area of light and moderate salinized soils is comparatively small, which accounts for only 0.4% and 4.6%, respectively.Quantitative evaluation Soil salinity Spatial distribution Electromagnetic induction Yellow River Delta

Effect of Biochar Application on Soil Fertility, Nitrogen Use Efficiency and Balance in Coastal Salt-Affected Soil under Barley–Maize Rotation

Coastal lands are often affected by salinization, which leads to a deterioration of soil structure and a decrease in land productivity. As a widely used soil amendment, biochar has been proven to improve poor soil properties and promote crop growth and N adsorption and utilization. However, the effects of biochar on soil fertility, N use efficiency (NUE) and balance in coastal salt-affected soil have rarely been reported. Therefore, we conducted a field micro-plot experiment to study the improvement effects of different biochar rates (0, 13.5, 20.25 and 27 t/ha, corresponding to CK, B1, B2 and B3 treatments, respectively) on coastal salt-affected soil. The results showed that biochar application increased soil water content (SWC) in seasons with abundant rainfall but decreased SWC in seasons with strong evaporation, and the increase or decrease in SWC was greater with the increase in biochar rates. Biochar application increased soil salinity and decreased soil pH, although high rates of biochar increased soil salinity to a lesser extent, while low rates of biochar decreased soil pH most. Biochar application was able to reduce soil bulk density, while B1and B2 treatments decreased it to a higher degree. Moreover, biochar application increased soil macro-aggregates (>0.25 mm) and organic matter, while B2 and B3 treatments increased it to a higher degree. Biochar application improved soil fertility to an extent that crop grain increased yield by 2.84~19.88% in barley season and 12.27~16.74% in maize season. Meanwhile, biochar application also increased NUE because it promoted the increase of yield. In particular, the calculation of N balance between soil and plant systems suggested that biochar application could reduce the apparent N loss during crop planting, and B1 treatment was better at reducing apparent N loss. Overall, our study indicates that biochar application has great potential to improve poor physicochemical properties and N nutrient utilization in coastal salt-affected soil. More importantly, we suggest that biochar application rates should be controlled in coastal salt-affected soil

Manure plus Plastic Film Mulch Reduces Soil Salinity and Improves Barley-Maize Growth and Yield in Newly Reclaimed Coastal Land, Eastern China

In newly reclaimed coastal soil, saline conditions and nutrient deficiency are the restraining factors for crop yield. Manure and plastic film mulch are proved to play a vital role in reducing soil salt, increasing soil water, and improving soil nutrients and plant growth. A field experiment was carried out with plastic film mulch, manure, and their combinations in the Tiaozini reclamation area; four treatments were set up as (1) control treatment (CK), (2) plastic film mulch (PM), (3) farmyard manure (FM), and (4) combined application of plastic film mulch and farmyard manure (PM+FM). The main results showed that, compared with CK treatment, the average soil water content under the FM+PM treatment was increased by 5.8% and 3.6%, and the average soil salt content was reduced by 20.2% and 10.0% at 0–20 cm and 20–40 cm soil layers, respectively. This was because of the decrease in soil bulk density and increase in saturated hydraulic conductivity and saturated water content. Meanwhile, soil organic matter, total nitrogen, available nitrogen, and available phosphorus were significantly increased under the PM+FM treatment, except that for AN, which was significantly decreased at the 0–10 cm soil layer owing to plant uptake. Based on the decrease in soil salt, there was an improvement in soil hydraulic properties and soil nutrients, which resulted in summer maize biomass and yield being increased by 106% and 137%, respectively, and barley biomass and yield were increased by 133% and 106%, respectively, under FM+PM treatment. Consequently, combined manure and plastic film mulch application was better at reducing soil salt; increasing soil water content; and improving soil nutrients, plant growth, and yield production in newly reclaimed salt-affected soils

The Effect and Influence Mechanism of Soil Salinity on Phosphorus Availability in Coastal Salt-Affected Soils

Soil salinization is a problem that arouses the world’s attention. Soil salinity is an important limitation for agriculture production in coastal area. Phosphorus is a very important nutrient element in the process of plant growth, and its effectiveness affects plant growth to a great extent. In this study, soil available phosphorus and its component in Hedley phosphorus classification were found to be affected by soil salinity in coastal areas of Jiangsu Province. Several key environmental factors changed under the saline environment of the coastal areas, such as soil salinity, soil pH, and soil alkaline phosphatase activity. These environmental factors were significantly correlated with soil available phosphorus. Results showed that there were significant correlations between soil salinity and other environmental factors, and soil salinity and alkaline phosphatase activity were the main influencing factors of soil available phosphorus in this study. Significant positive correlation was found between alkaline phosphatase activity and soil salt content, and soil salinity was considered as the most important impact factor for soil available phosphorus as it affected the surrounding environment, and the soil alkaline phosphatase could be considered as the direct influencing factor for soil available phosphorus. Analysis between the soil alkaline phosphatase activity and phosphorus component showed that soil alkaline phosphatase activity could increase the proportion of active inorganic phosphorus and medium active inorganic phosphorus in soil phosphorus pool, which explained the effect of soil alkaline phosphatase activity on soil available phosphorus

Manure plus Plastic Film Mulch Reduces Soil Salinity and Improves Barley-Maize Growth and Yield in Newly Reclaimed Coastal Land, Eastern China

In newly reclaimed coastal soil, saline conditions and nutrient deficiency are the restraining factors for crop yield. Manure and plastic film mulch are proved to play a vital role in reducing soil salt, increasing soil water, and improving soil nutrients and plant growth. A field experiment was carried out with plastic film mulch, manure, and their combinations in the Tiaozini reclamation area; four treatments were set up as (1) control treatment (CK), (2) plastic film mulch (PM), (3) farmyard manure (FM), and (4) combined application of plastic film mulch and farmyard manure (PM+FM). The main results showed that, compared with CK treatment, the average soil water content under the FM+PM treatment was increased by 5.8% and 3.6%, and the average soil salt content was reduced by 20.2% and 10.0% at 0–20 cm and 20–40 cm soil layers, respectively. This was because of the decrease in soil bulk density and increase in saturated hydraulic conductivity and saturated water content. Meanwhile, soil organic matter, total nitrogen, available nitrogen, and available phosphorus were significantly increased under the PM+FM treatment, except that for AN, which was significantly decreased at the 0–10 cm soil layer owing to plant uptake. Based on the decrease in soil salt, there was an improvement in soil hydraulic properties and soil nutrients, which resulted in summer maize biomass and yield being increased by 106% and 137%, respectively, and barley biomass and yield were increased by 133% and 106%, respectively, under FM+PM treatment. Consequently, combined manure and plastic film mulch application was better at reducing soil salt; increasing soil water content; and improving soil nutrients, plant growth, and yield production in newly reclaimed salt-affected soils

Effect of Different Fertilization Measures on Soil Salinity and Nutrients in Salt-Affected Soils

Saline soil from the coast is a valuable and readily available resource. It is also a valuable resource for reserving arable land. Adding organic fertilizers to salinized soils is an effective method of enhancement. However, saline soils cannot be improved using a single measure, and the effects of compound measures of organic fertilizers combined with mineral elements, such as humic acid, are significant and worthy of further examination. To explore the effects of various measures on the features of pH, electrical conductivity (EC), and nutrient changes in coastal salinized soils in Yancheng, Jiangsu Province, a ryegrass–alfalfa rotation with organic fertilizer and compound measures was designed. The findings indicated that the total nitrogen (TN) content of the soil increased and that all organic fertilizer composites decreased the electrical conductivity of the surface soil. However, the organic fertilizer with microbial fertilizer and humic acid was especially effective at regulating the pH and electrical conductivity of the surface soil when salts were prone to accumulation. In conclusion, our findings highlight new approaches to lowering salinity and boosting fertility in coastal saline soils: organic fertilizer with microbial fertilizers and humic acid, as well as organic fertilizer with attapulgite clay

Nitrate leaching and NH3 volatilization during soil reclamation in the Yellow River Delta, China

The agricultural ecological system is an important part of the Yellow River Delta (YRD); however, soil reclamation may trigger environmental concerns about nitrate leaching and NH3 volatilization in this area. To assess nitrogen losses during soil reclamation, a two-year field experiment was conducted with plastic film mulch, which is an effective way to alleviate water-salt stress. The Hydrus-2D software package was used to calculate nitrogen transport, transformation and losses. The results showed that nitrogen (N) retention in the soil varied during the two growing seasons, because soil water, salinity and climatic conditions acted together on nitrogen transport and transformation. Soil salinity promoted NH3 volatilization, and the proportions of ammonia volatilization were 22.78 percent and 19.50 percent of the N input in 2018 and 2019, respectively, because urea hydrolysis, nitrification and soil NH4+ - N adsorption capacity were limited by soil salt. NO3- - N leaching was controlled by soil water infiltration, climatic conditions and groundwater level. NO3- N leaching was 43.84 percent and 32.89 percent of the nitrogen input in 2018 and 2019, respectively; the difference was mainly caused by the different distribution of rainfall during the growing season; thus, soil water infiltration increased under heavy rainfall because it broke the barrier formed by the plough pan. This study indicates that there is a risk of nitrogen pollution during soil reclamation. In addition, Hydrus-2D has considerable potential to calculate nitrogen losses under the effect of plastic film mulch in this area

MULTIVARIATE SIMULATION AND ASSESSMENT OF THREE DIMENSIONAL SPATIAL PATTERNS OF COASTAL SOIL SALINITY USING ANCILLARY VARIABLES

Rapid and reliable spatial estimates of field soil salinity aid farmers and researchers in understanding the development of salinization and identifying areas in the field where special management practices are required to control its speed. Apparent soil electrical conductivity, measured by electromagnetic induction instruments, has been widely used as an auxiliary variable to estimate spatial distribution of field soil salinity owing to the high-efficient and non-invasive nature. Methods used for this purpose are mostly a series of kriging-based algorithms. This study adopted stochastic simulation algorithms, sequential Gaussian simulation (SGS) and sequential Gaussian co-simulation (SGCS), to generate equiprobable realizations of soil salinity patterns, to evaluate the uncertainty associated with those patterns, and to determine which algorithm is more reliable for the local and spatial uncertainty assessment. Results showed that experimental semivariograms were generally isotropic at all directions with the identical nugget, sill and range parameters despite the limited data in X and Z directions. Nugget contributions comprised from 19.5 to 40.1% of model sill values at the horizontal orientation, which negligibly ranged from 2.1 to 6.0% at the vertical orientation. The spatial patterns of soil salinity generated by SGS and SGCS algorithms showed consistency with the actual values. It was found that the distribution of soil salinity was generally normal and there existed the probability of secondary salinization across the spatial domain. The estimation precision of SGS algorithm was superior to that of SGCS algorithm. In addition, accuracy plots and standard deviation maps both indicated that SGS approach performed better in terms of modelling local uncertainty and propagating the spatial uncertainty. Thus, the SGS method was suitable for the spatial estimation of the soil property, distribution type and data arrangement in our study. We concluded that the SGS algorithm with data conversion (converting EM measurements at unsampled sites to soil salinity values) prior to simulation modeled the uncertainty better than the SGCS algorithm (soil salinity as primary variate and EM measurements as covariate)

Chemical Fertilizer Reduction Potential Estimation and Fertilization Optimization Strategy Based on a 10-Year Application Summary and Status Questionnaires in a Typical Yellow River Irrigated Area

The Yellow River Delta is an important grain production base in China, and it is a typical Yellow River irrigated area. Chemical fertilizer overuse has seriously affected grain production safety, and understanding the fertilizer application situation is useful for scientific agronomy management. In this study, we collected the data of the N, P, K fertilizers for crop cultivation in Donging City from 2011 to 2020, and we collected 185 investigating questionnaires to gather information on the fertilizer application rate for small farmers. The results showed that the amount of total fertilizer used has decreased from the year 2015, but the macro element fertilizer rate for crop cultivation exceeded the recommended dosage. The application of compound fertilizer increased during the investigated 10 years, and its proportion in 2020 was 1.65 times higher than in 2011. For obtaining an ideal grain yield, the N and P2O5 had relative reduction rates of 67.8% and 69.6% for wheat planting. Furthermore, the relative reduction rates of N, P2O5, and K2O were 25.9%, 69.6%, and 59.7%, respectively, for maize cultivation when compared to the recommended dosage. During wheat growth, the potassium fertilizer was needed to increase the dosage, although the K element content in the soil was high. Furthermore, the medium and trace elements are all important nutrients for improving crop yield and quality which need to be studied. More scientific measurements should be conducted to match chemical fertilizer reduction to constructing healthy and sustainable agriculture in the Yellow River irrigated area