Evaluation of groundwater quality in agricultural areas

The quality of irrigation water in agricultural areas should generally be suitable for the normal growth requirements of crops, to ensure the quality of agricultural products, as well as to protect the soil and groundwater sources from pollution. To evaluate the water quality of agricultural irrigation water, it is generally necessary to consider the water temperature, pH value, salt content, salt composition, the relative proportion of sodium ions and other anions, boron and other toxic elements, such as the concentration of indicators.

Referring to China's "Agricultural Irrigation Water Quality Standards" (GB5084-92) and domestic and foreign standards for agricultural irrigation water quality, in addition to the above wide range of evaluation methods, should also be selected in the agricultural area of practical methods: sodium adsorption ratio (SAR), irrigation coefficient (Ka), total mineralization (M) and other methods (Hydrogeology Manual. 1978).

(I) Sodium Adsorption Ratio (SAR) method

Sodium Adsorption Ratio (SAR) is the relative ratio of sodium ions to calcium and magnesium ions in the water, and its calculation formula is

Regional Groundwater Functions Sustainability Evaluation Theory and Methods

(II) Irrigation Coefficient Ka method

The irrigation coefficient refers to the amount of water that has evaporated after a certain thickness of water layer. A certain thickness of water layer all evaporation of salts left behind, can make 1.2m soil layer salt accumulation, so that most of the crops can not grow, the thickness of this water layer (m) that is, the irrigation coefficient, which is based on the salts of 40 kinds of crops on the maximum harm and sodium salt relative harm to the experiment, the specific method of calculation is shown in Table 4-7.

Table 4-7 Calculation method of irrigation coefficient Ka

Note: 288 is a constant; rCl-, rNa+, respectively, for its ionic concentration (molar).

Through the calculation of sodium adsorption ratio (A), irrigation coefficient (Ka), combined with the total mineralization (M) to evaluate the grading of farmland irrigation water, the grading standards are shown in Table 4-8.

Table 4-8 Agricultural irrigation water quality grading table

Note: the unit of mineralization is g/L.

(C) Salinity, alkalinity and mineralization index method

This evaluation method is shown in Table 4-9, and the evaluation indexes are shown in Table 4-10.

Table 4-9 Evaluation method of salinity, alkalinity, and mineralization of agricultural water

Table 4 -10 Salinity, alkalinity, mineralization evaluation of farmland water quality indicators

(D) Comprehensive Hazard Coefficient Method

Comprehensive Hazard Coefficient (K) is calculated as

K=12.4M+SAR (4-62)

In the formula: K is the comprehensive hazard coefficient, reflecting the degree of comprehensive hazards; M is the degree of mineralization of irrigation or groundwater (g/L), reflecting salt hazards; SAR is the degree of salinity; and SAR is the degree of salinity. ), reflecting salt damage; SAR is the sodium adsorption ratio, reflecting alkali damage.

Comprehensive hazard coefficient evaluation of water quality standards are shown in Table 4-11.

Table 4-11 Comprehensive Hazard Coefficient Evaluation of Irrigation Water Quality Table