**10. Management strategies for phosphorus to protect the environment**

#### **10.1 Phosphorus in the soil**

Apatite and other primary minerals are the principal sources of P in the environment (calcium phosphate). Many rocks and soils include phosphate-bearing minerals. It takes time for these minerals to break down and release phosphorus into the soil. P is a highly reactive substance in the environment. This orthophosphate exists in a variety of different phosphate forms in solution, depending on the acidity. In the absence of rapid uptake by plants or soil micro-organisms, orthophosphate is likely to recombine with other soil chemicals (e.g., calcium, iron, aluminum, and manganese). As a result, P has long been regarded as the most important agricultural nutrient.

#### **10.2 Phosphorus in the agriculture**

Commercial, inorganic, phosphate fertilizers have been used to correct soil P-deficiency over the past 50 years. Plants can benefit from phosphate fertilizers because they are made by removing P from phosphate-rich rocks and making them more accessible. P has built up in agricultural soils due to massive volumes of these fertilizers over many decades. Crop yields are not adversely affected by soils with high P-reserves, except for the availability of micronutrients such as zinc. Before the 1970s, the practice of using high-phosphate fertilizers to increase soil phosphorus reserves was encouraged, and it was equated to "saving money in the bank." According to conventional belief, having high soil P-levels was equivalent to having significant cash in the bank. As a result of growing worries about the association between high soil P levels and the harm to water quality posed by P-rich soil particles entering the water through runoff, this concept has come under scrutiny in recent years.

#### **10.3 Controlling runoff in case of agricultural phosphorus**

Phosphate fertilizers, plant waste, manure, and agricultural effluent should not be directly applied to surface waters to prevent point source P-contamination. Pollution caused by nonpoint P-sources such as agricultural fields can be reduced by regulating the amount and kind of runoff. To avoid P pollution from surface waters, areas with steep slope and highly erodible soils close to surface waters should be avoided. A site's risk of becoming a prospective polluter can be considerably affected by management approaches. Sediment can be reduced significantly with the use of cover crops and buffer strips. Another factor that can enhance the risk of contamination is a lack of soil cover or barriers between a farm and its water.

Generally, water erosion happens on slopes, and the intensity of the decline increases with the slope's degree. Using no-till farming can reduce soil erosion. Additionally, crop residues can be left on the soil surface after harvest, and winter cover crops can be planted in the fall. Reduced water erosion can be achieved through the use of contoured tillage. Rather than going up and down the slope, plows are used to plow across it. The geometry of some fields makes this technique ineffective. To decrease water erosion, terraces can also be built. Soil erosion can be reduced by leaving agricultural remains on the field after harvesting. Leaving corn stalks on the field after harvest is one example of how crop residues can protect the soil from eroding throughout the winter. The residues protect the soil surface until the land is plowed, reducing the time it is exposed to the weather.

Protecting the soil from erosion during noncrop months is done by planting cover crops, such as grasses, legumes, or small grains. Once the main crop is planted, they remain in the field. Phosphorus levels in rivers and streams are reduced by cover crops, which reduce erosion. Cover crops can also take up P and other nutrients while other crops are not growing. Wildlife can also benefit from cover crops, which give food and shelter.

#### **10.4 Management of fertilizer phosphorus sources**

In agricultural runoff, the most prevalent sources of P are manure and compost, as well as mineral fertilizers [111]. Practices that can reduce the risk of agricultural land contamination with P include limiting the amount, timing, and method of application of P-fertilizer sources. There is a strong correlation between soil test P-levels
