Effects of irrigation with HCH-contaminated water on crop performance and HCH accumulation in plant and soil

Lindane production is very ineffective since, for each ton of lindane obtained, between 6 and 10 tons of hexachlorocyclohexane (HCH) isomers and other toxic compounds are produced. Due to the disposal of these residues, contaminated zones still exist, and many dumpsites are close to rivers and water reservoirs. The current study examines the consequences of irrigating pea, maize, and alfalfa, with water containing different HCH concentrations on the accumulation of HCH in plant material and soils. The experiments were conducted on pots under controlled conditions using drinking water (as reference) and water with several HCH concentrations: 0.5 μg L^-1 (the maximum threshold allowed for human consumption), 2.5 μg L^-1, 5 μg L^-1, and 20 μg L^-1. Results showed that both surface and overhead irrigation with these HCH concentrations did not cause any toxicity effects on the considered crops. However, under overhead irrigation with HCH concentrations higher than 5 μgL^-1 HCH is absorbed by maize leaves and its concentration in plant biomass surpassed the EU maximum residue level of 10 μg kg^-1. In the case of fodder maize, an HCH concentration of 0.84 μg L^-1 in irrigation water produced an HCH concentration in plant above 20 μg kg^-1 dry matter, the upper threshold established in the Spanish legislation, that limits the use for animal feeding. In the case of alfalfa, HCH was detected in treatments with the highest HCH concentration (13 μg L^-1) under surface irrigation, but concentration was below the EU maximum residue level. In conclusion, in overhead irrigated systems, water with HCH concentrations below 5 μg L^-1 does not produce HCH accumulation in pea and maize grain above the maximum residue levels; however, for fodder maize, the HCH concentration in irrigation water should be controlled to avoid HCH accumulation in plants above the limit for animal feeding.

Coupled DSSAT-SWAT models to reduce off-site N pollution in Mediterranean irrigated watershed

In any agricultural watershed, best management practices (BMPs) are a conservational way to reduce non-point source pollution and, soil and water resources sustainability. The objectives of this study were to calibrate and validate the modified Soil and Water Assessment Tool (SWAT) in the Violada Watershed (VW), Spain and assess the BMPs scenarios, already tested at field scale, using the Decision Support System for Agro Technology Transfer model (DSSAT), and finally, to access the BMPs impact on water quality off-site. To this end, daily streamflow discharge and NO₃^- concentration were measured at VW outlet from October 2015 to September 2017 for model evaluation. The SWAT-CUP was used for sensitivity analysis, calibration and validation for both measured variables after manual calibration of the main crops yield. Three management scenarios were compared to the current conditions (baseline): (i) recommended N fertilization, (ii) optimum irrigation and; (iii) combined recommended N fertilization and optimum irrigation (combined BMPs). The SWAT crop growth model calibration demonstrated that the annual average of crop yield and actual evapotranspiration estimations were satisfactory. Monthly calibration and validation results were satisfactory for streamflow discharge and NO₃-N load, with Nash-Sutcliffe efficiency (NSE) according to the criteria reported in the literature. The two individual scenarios results showed difference in their environmental impact and therefore combined BMPs scenario was considered more efficient in reducing NO₃-N load (51%) than the recommended N fertilization (36%) and the optimum irrigation (12%), while including all additional environment and farmers' benefits of both individual scenarios. Under this combined scenarios, all crops yields were maintained or increased, and the total irrigation water and N mineral fertilizers application reduction were about 5% and 27%, respectively. However, further work is still needed to consider additional BMPs to limit the soil N residual losses during the non-cropped period. The applied methodology can be a good alternative for improving water quality in similar irrigated watersheds.

Risk of phosphorus desorption from Canadian agricultural land: 25-year temporal trend

Phosphorus (P) use in excess of crop needs may impact surface water quality and contribute to eutrophication. However, P loss from agricultural land to water has never been estimated at the Canadian national scale. In this paper, the risk of P desorption from Canadian agricultural land is assessed by the source component of the indicator of risk of water contamination by P (IROWC-P). The IROWC-P source component (P_source) characterized the mobilization potential of soluble P and integrated four models of P desorption by water for dominant agricultural soil series of Canada on the soil landscape of Canada polygon scale (1:1,000,000). The objective of our study was to describe and evaluate a standardized method for deriving the P_source component. The P_source was assessed over 5-yr intervals from 1981 to 2006 for scientifically based knowledge by relating annual P balance values, soil test P (STP) analyses, soil P saturation index, and Self-Davis water extractable P extraction values. Results show trends of soil P enrichment for most Canadian provinces over the 25-yr period but also an increased percentage of farmland classified above the water extractable soil P environmental threshold of 4 mg P kg. The Canadian Prairies and Ontario showed small P_source values and almost no farmland above the environmental threshold. Quebec and the Atlantic Provinces had P_source values that exceeded the environmental threshold in 2006; more than 33% of farmland is classified above the environmental threshold value.

Indicator of risk of water contamination by phosphorus from Canadian agricultural land

The indicator of risk of water contamination by phosphorus (IROWC_P) is designed to estimate where the risk of water P contamination by agriculture is high, and how this risk is changing over time based on the five-year period of data Census frequency. Firstly developed for the province of Quebec (2000), this paper presents an improved version of IROWC_P (intended to be released in 2008), which will be extended to all watersheds and Soil Landscape of Canada (SLC) polygons (scale 1:1, 000, 000) with more than 5% of agriculture. There are three objectives: (i) create a soil phosphorus saturation database for dominant and subdominant soil series of SLC polygons--the soil P saturation values are estimated by the ratio of soil test P to soil P sorption capacity; (ii) calculate an annual P balance considering crop residue P, manure P, and inorganic fertilizer P--agricultural and manure management practices will also be considered; and (iii) develop a transport-hydrology component including P transport estimation by runoff mechanisms (water balance factor, topographic index) and soil erosion, and the area connectivity to water (artificial drainage, soil macropores, and surface water bodies).