Site-specific management of salt affected soils: A case study from Egypt

Matching N supply for yield maximization in salt-affected wheat agri-food systems: On-farm participatory assessment and validation

Driven by the UN-SDGs of achieving food security and agricultural sustainability, it remains more challenging in degraded ecosystems to simultaneously improve the crop performance without creating unintended favour for excessive fertilization and associated environmental consequences. We assessed the N-use pattern of 105 wheat-growers in sodicity affected Ghaghar Basin of Haryana, India, and then experimented upon to optimize and identify indicators of efficient N use in contrasting wheat cultivars for sustainable production. The survey results revealed that majority of farmers (88%) have increased their reliance on N nutrition (∼18 % extra N), and even extended their duration of N scheduling (12-15 days) for better plant adaptation and yield insurance in sodicity stressed wheat; albeit to a greater extent in moderately sodic soils applying 192 kg N ha^-1 in 62 days. The participatory trials validated the farmers' perception of using more than the recommended N in sodic lands. This could realize the transformative improvements in plant physiological [higher photosynthetic rate (Pn; 5 %) and transpiration rate (E; 9 %)] and yield [more tillers (ET; 3 %), grains spike^-1 (GS; 6 %) and healthier grains (TGW; 3 %)] traits culminating in ∼20 % higher yield at 200 kg N ha^-1 (N₂₀₀). However, further incremental N application had no apparent yield advantage or monetary benefits. At N₂₀₀, every additional kilogram of N captured by the crop beyond the recommended N improved grain yields by 36.1 kg ha^-1 in KRL 210 and 33.7 kg ha^-1 in HD 2967. Further, the varietal differences for N requirements, with 173 kg ha^-1 in KRL 210 and 188 kg ha^-1 in HD 2967, warrants the need of applying balanced fertilizer dose and advocate revision of existing N recommendations to cope up the sodicity induced agricultural vulnerability. Principal Component Analysis (PCA) and correlation matrix showed N uptake efficiency (N_UpE) and total N uptake (TNUP) as the highly weighted variables illustrating strong positive association with grain yield, and potentially deciding the fate of proper N utilization in sodicity stressed wheat. Key insights suggested that combining participatory research with farmers' knowledge and local perspective could be decisive in better integration of technologies, and serving to adapt the real-time soil sodicity stress and sustaining wheat yields with economized farm profits.

Delineating reclamation zones for site-specific reclamation of saline-sodic soils in Dushak, Turkmenistan

Soil salinization is the widespread problem seriously affecting the agricultural sustainability and causing income losses in arid regions. The major objective of the study was to quantify and map the spatial variability of soil salinity and sodicity. Determining salinity and sodicity variability in different soil layers was the second objective. Finally, proposing an approach for delineating different salinity and sodicity zones was the third objective. The study was carried out in 871.1 ha farmland in Southeast of Dushak town of Ahal Province, Turkmenistan. Soil properties, including electrical conductivity (EC), soil reaction (pH), sodium adsorption ratio (SAR), calcium carbonate and particle size distribution (clay, silt and sand fractions) in 0-30, 30-60, 60-90 and 90-120 cm soil layers were recorded. The EC values in different soil layers indicated serious soil salinization problem in the study area. The mean EC values in 0-90 cm depth were high (8 dS m-1), classifying the soils as moderate to strongly saline. Spatial dependence calculated by the nugget to sill ratio indicated a strong spatial autocorrelation. The elevation was the primary factor affecting spatial variation of soil salinity in the study area. The reclamation of the field can be planned based on three distinct areas, i.e., high (≥12 dS m-1), moderate (12-8 dS m-1) and low (<8 dS m-1) EC values. The spatial trend analyses of SAR values revealed similar patterns for EC and pH; both of which gradually decreased from north to the south-west. The amount of water needed to leach down the salts from 60 cm of soil profile is between 56.4-150.0 ton ha-1 and the average leaching water was 89.8 tons ha-1. The application of leaching water based on the amount of average leaching water will result in higher or lower leaching water application to most locations and the efficiency of the reclamation efforts will be low. Similar results were recorded for sulfur, sulfuric acid and gypsum requirements to remediate sodicity. The results concluded that the best management strategy in planning land development and reclamation schemes for saline and sodic soils require accurate information about the spatial distribution of salinity and sodicity across the target area.

A combined geostatistical approach of data fusion and stochastic simulation for probabilistic assessment of shallow water table depth risk

In general, water table depth risks are estimated from monitoring networks that mostly provide scarce and irregular data. When jointly analysed, environmental, agricultural and geotechnical variables, treated as stochastic spatial variables, can better describe and interpret the states of a certain system subject to estimation uncertainty. Risk assessment consists essentially in calculating the frequency (probability) with which specified criteria are exceeded or fail to be met by creating multiple stochastic realizations. The aim of this paper is to propose a novel geostatistical methodology, based on the integration into one approach of multi-source data fusion and stochastic simulation, to estimate the risk of extreme (shallow) water table depth, and illustrate a demonstrative example of application of the approach to a case study in a Cerrado conservation area in Brazil. The risk of shallow water table depth was determined by using critical thresholds for water table level and a binary transformation into an indicator variable depending on whether the conditions expressed by the threshold values are met or not. Firstly, auxiliary variables were jointly, analysed to provide a delineation of the study area into homogeneous zones. Secondly, sequential indicator simulation provided a-posteriori probabilities taking into account spatial proximity. The final maps show the most probable risk category for the whole area and spatial entropy as a measure of local uncertainty. Areas nearby watershed divisors and in the north part of the region have a high risk of shallow groundwater. Informed decision-making supported by probabilistic maps and uncertainty evaluation is essential for the success of the projects of Cerrado restoration.

Soil Properties Spatial Variability and Delineation of Site-Specific Management Zones Based on Soil Fertility Using Fuzzy Clustering in a Hilly Field in Jianyang, Sichuan, China

Avoiding soil degradation and improving crop productivity could be achieved by performing sustainable soil nutrient management with an appropriate understanding of soil properties’ spatial variability. The present fertilizer recommendations for the region where the study area is located are typically symmetric for large regions. This leads to the under-application of fertilizers in zones with low nutrient contents and over-application in zones with high nutrient contents. Therefore, this study was conducted to assess soil management zones (MZs) in the study area for effective soil nutrient management and to evaluate soil properties’ spatial variability. A total of 100 geo-referenced soil samples were collected at a depth of 0–20 cm, processed and analyzed for pH, available nitrogen (AN), available phosphorus (AP), available potassium (AK), soil organic carbon (SOC), total nitrogen (TN) and total phosphorous (TP), while C:N, C:P and N:P ratios were calculated. Soil properties’ coefficients of variation (CVs) widely varied from low (1.132%) to moderate (45.748%). Ordinary kriging and semi-variogram analysis showed differed spatial variability patterns for the studied soil properties with spatial dependence ranged from weak to strong. MZs were delineated by performing principal component analysis (PCA) and fuzzy K-means clustering. Four PCs with eigen values more than 1 dominated 84.44% of the total variance, so they were retained for clustering analysis. Three MZs were delineated based on the two criteria modified partition entropy (MPE) and fuzzy performance index (FPI). The studied soil properties differed significantly among MZs. Thus, the methodology used for MZ delineation could be used effectively for soil site-specific nutrient management for avoiding soil degradation concurrently with maximizing crop production in the study area.