tailieunhanh - Applications of Environmental Aquatic Chemistry: A Practical Guide - Chapter 10 (end)

Hầu hết chất lượng nước liên quan đến vấn đề nông nghiệp tưới tiêu trong mùa thu vào loại lò nướng thông thường: 1. Độ mặn cao: hòa tan muối (Tổng số hòa tan muối [TDS]) trong nước các tháng Giảm nguồn nước cho các nhà máy đến Mức độ đó sản lượng cây trồng bị ảnh hưởng IS. Hiệu ứng này gây ra bởi một IS Giảm áp suất thẩm thấu của các nhà máy đó có thể exertions của họ qua màng gốc cho hấp thụ nước. Vấn đề độ mặn thường có thể được giảm nhẹ bằng. | 10 Selected Topics in Environmental Chemistry AGRICULTURAL WATER QUALITY Most water quality-related problems in irrigated agriculture fall into four general types 1. High salinity Dissolved salts total dissolved salts TDS in the water may reduce water availability to the plants to the extent that crop yield is affected. The effect is caused by a lowering of the osmotic pressure that the plants can exert across their root membranes for absorbing water. Salinity problems can often be mitigated by proper irrigation practices. 2. Low water infiltration rate Relatively high sodium or low calcium and magnesium content of the water may reduce the water permeability of the soil to the extent where sufficient water cannot flow through the root zone at an adequate rate for optimal plant growth. The effect is caused when an excess of sodium ions adsorbed on clay particles causes the soils to swell thereby reducing pore size and water permeability. An empirical indicator the sodium absorption ratio SAR measures the excess of sodium over calcium and magnesium and provides a guide to potential soil permeability problems see Section . 3. Specific ion toxicity Certain ions can accumulate in the leaves of sensitive crops to concentrations high enough to cause crop damage and reduce yields. Ion toxicity arises mainly from sodium chloride and boron. Other trace elements are also toxic to plants in low concentrations but generally are present in groundwater in such low concentrations that they seldom are a problem. In general concentrations of concern for specific ion toxicity are lower for sprinkler irrigation than for surface irrigation because toxic ions can be absorbed directly into the plant through leaves wetted by the sprinkler water. Direct leaf absorption speeds the rate of accumulation of toxic ions. 4. Nutrient imbalance Nitrogen ion concentrations can be too high resulting in excessive vegetative growth weak supporting stalks delayed plant maturity and poor crop