Implement Nutrient Management Techniques An easy way to improve nutrient management techniques practices is by ensuring you are applying the fertilizer in the right amount, at the right time of the year, using the correct method and in the right spot.
Control Livestock Access to Waterways Installing fences along any streams, rivers or lakes to keep livestock out of them can help restore the stream banks. Minimize Tillage Using a more conservative tillage schedule can help reduce erosion, runoff and soil compaction, which helps reduce the chances of nutrients reaching waterways or non-owned land. Have a Manure Management Plan Along with having an accurate nutrient management technique, having a manure management plan is important to preventing agricultural pollution.
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In USA, agricultural non-point source pollution is considered the dominant source of nutrients in lakes and streams [ 13 ]. Appropriate management of agricultural runoff and animal waste is a large concern for the U. Its main sources of excess water are from irrigation and rainfall [ 14 ]. Agricultural runoff has complex pollutant compositions including nitrates, ammonium, phosphorus compounds, heavy metals, and persistent organic pollutants. N and P, being essential elements in amino acids and genetic material, respectively, are vital to the growth of aquatic plants as the key limiting nutrients during eutrophication [ 15 ].
Anthropogenic eutrophication has become the primary problem as it is often recognized to have strong potentials to affect the health and security of aquatic ecosystems in the world. At the same time, continuous input of heavy metals and persistent organic pollutants POPs from agricultural runoffs can easily accumulate in organisms to pose various health risks e.
Therefore, it is of considerable interest to adequately decrease agricultural non-point source pollution to control eutrophication in lakes and rivers, to protect the water environment, and to secure drinking water quality. There are three main control strategies for agricultural runoff pollution: source control, process control, and end treatment. Source control works to reduce the application of N and P as well as leaching, such as conservation tillage, fertilization management, and water-saving irrigation [ 18 , 19 , 20 ].
Process control aims to eliminate the pollutants by using the space and time of agricultural runoffs from the field to the receiving water, such as ecological ditches [ 21 ]. They are usually set in the agricultural ditches. End treatment is the last choice to avoid the damage of the receiving water, if the pollutants does not fall below the safe value [ 22 ]. The large storage capacity provides more time for the treatment of agricultural runoffs. Although each approach is based on different principles, they serve to control agricultural runoff pollution to varying degrees.
It is difficult to find efforts to integrate the diverse treatment options from source to end. In this review, we highlight current mainstream technologies along with some promising alternatives. A scenario analysis based on the reference data was also made to provide a comprehensive understanding of the current control techniques for agricultural runoff and their roles in effective control of agricultural runoff.
Agriculture supports the construction and development of a national economy. It is of particular importance to the most populated countries, such as China, India, and Indonesia [ 23 ]. Due to the great demand for food, the use of chemical fertilizers and pesticides has become indispensable over the past decades [ 24 ].
The N and P fertilizers have been used most widely in the world. The USA is still increasing their use of fertilizers. Moreover, China is the largest producer and consumer of fertilizers. Overuse of chemical fertilizers leads to various environmental problems including surface water eutrophication, N-related greenhouse gas emissions, and groundwater pollution [ 25 , 26 , 27 ].
Although the application of fertilizer is made to the farmland, the transport of excess N and P takes place by surface water runoff after rainfall and irrigation events. As shown in Fig. As the main component of an agricultural irrigation system, ditches can act as the major pathway of farmland surface runoff.
Since agricultural runoff undergoes a certain amount of migration time before discharging to the receiving water, ditches can be an ideal place for controlling on N and P [ 28 ]. The diffusivity of N and P differs greatly in soils.
Cookson et al. In this case, the N and P discharge rates were estimated as Although the loss load of nutrients varies little from year to year, it varies greatly from month to month. For instance, the highest N and P loss concentrations took place over April, June, July, and August in China, which correspond to the high-risk eutrophication period [ 32 ]. The unevenness of time distribution of loss load greatly increases the difficulty of controlling nutrient loss from agricultural runoff.
As a major form of non-point source agricultural pollution, continuous N and P input leads to their accumulation in the receiving water. Excessive N and P accumulation causes various problems such as algal blooms, water degradation, fish kills, and loss of biodiversity [ 33 ].
Due to the lack of effective control on agricultural non-point pollution, N and P pollution has become a global problem. In China, over half of the major lakes are eutrophic while nearly three quarters are continuously deteriorating [ 35 ]. Even in Canada, the deterioration of lake Winnipeg is also attributed to excessive N and P nutrient enrichment [ 36 ].
Therefore, controlling N and P from agricultural runoff is urgent. Dissolved pesticides, nutrients, and sediments in agricultural runoff cause various problems, including persistent organic translocation, nutrient loss, and soil erosion [ 37 ]. Reasonable tillage practices can significantly improve surface roughness and reduce surface runoff, thus reducing runoff emissions and pollution load at the source.
Rice requires a great deal of water, which leads to massive agricultural runoff [ 38 ]. The dissolved N, P and sediments create a huge pollution load on the surrounding waters [ 39 , 40 , 41 ]. Although, tillage inevitably disturbs the soil surface, conservation tillage methods such as reduced tillage and no-tillage play significant roles in protecting soil from erosion [ 42 ].
In addition, conservation tillage improves soil structure and increase organic matter content, which can increase the infiltration to runoff ratio and reduce evaporation [ 43 , 44 ].
Reduced tillage and no-tillage are both effective methods of conservation tillage. For example, Clausen et al. Liang et al. Reduced tillage and no-tillage reduce the intensity of tillage practices as well as the impact of rain by the protection of soil surface using crop residues.
In recent years, land covers and soil amendments such as biochar, which enhance the soil structure and porosity, are used to protect the soil [ 47 , 48 ]. Won et al. Lee et al. Accordingly, the field soils amended with biochar and polyacrylamide reduced soil loss by Biochar is often used in soil remediation, and it also has great potential in agricultural runoff control.
The effects of biochar on soil structure and nutrient fixation are worth further studies [ 52 , 53 ]. Conservation tillage is effective for reducing dissolved N in the runoff [ 54 ]. However, conservation tillage practices will inevitably lead to soil compaction during long-term operation, which will lead to P accumulation on the soil surface, and as a consequence, an increase in the runoff loss of P.
Tiessen et al. Rotation tillage is another choice to control nutrients loss in agricultural runoff. Liu et al. It is because tillage practices would alleviate soil compaction and decrease P accumulation in surface soil.
Crop residues in conservation tillage would capture more water that leads to greater runoff duration time. Therefore, rotation tillage could shorten the contact time between crop residues and surface runoff that reduces the P released from crop residues.
Daverede et al. Therefore, the selection of tillage practice should be based on local climatic conditions, soil conditions, crops, and dominant eutrophication nutrients. Fertilization management is another effective source control method that has been used widely [ 56 , 57 ]. Fertilizers containing N and P are commonly used in the agricultural industry. N-fertilizer efficiency varies from crop to crop.
In order to fully reflect the global nitrogen use efficiency NUE , Table 2 listed the world fertilizer N consumption for cereals, N removal in cereals, and estimated nitrogen use efficiency.
Once surface runoff is formed, excessive N and P would flow to the receiving water. Therefore, it is critical to deliberately manage fertilizer application. One example of fertilization management is deep placement of fertilizers to lower the risk of discharging N into a body of water. Fertilizer band placement and hole placement can reduce total N loss by This is because band placement can reduce contact with soil microorganisms and slow the nitrification process.
Zeng et al. These authors found that a 20 cm fertilization depth reduced TN and TP by Controlled-release of fertilizer is another choice that can lead to slow release of N and P to be adapted to the rate of crop growth while improving nutrient utilization efficiency [ 63 ]. Tan et al. Accordingly, the results indicated that controlled-release N fertilizer performed best in reducing inorganic N concentration in runoff.
Optimization of fertilizer timing and application rate is also important variables to control nutrient loss [ 66 ]. Because the losses show seasonal characteristics, with higher nutrient loading in summer and autumn.
As for rainfall process, nitrate-N loss increased gradually along with ammonia-N loss decreased. Based on these characteristics, model-based analysis has also been proposed for long-term effects of fertilization management [ 67 ].
Heavy precipitation and field drainage systems can drive surface runoff. This is because conventional flooding irrigation CFI keeps a high floodwater level in the fields. Water-saving irrigation WSI techniques could significantly reduce floodwater levels, improving the buffering capacity of the fields to help reduce runoff and nutrient losses.
Alternate Wetting and Drying AWD irrigation has also been employed widely to reduce water inputs and enhance water use efficiency in the rice cropping systems [ 70 , 71 , 72 ].
The AWD irrigation was seen to reduce surface runoff by The concentrations of nutrients, however, do not decrease with the decrease of surface runoff if AWD is applied alone. Because the contact time between water and soils will not decreased. Thus, it is better to integrate irrigation management with tilling practices and fertilization management. All the above source control techniques can effectively reduce surface runoff and nutrient concentrations. Nevertheless, they cannot prevent runoff from flowing into the receiving water.
The concentrations of N and P in agricultural runoff have decreased significantly by source control techniques. However, it is still difficult to achieve the safe discharge concentrations.
Because long-term accumulation of nutrients in receiving waters will also increase the risk of eutrophication. Therefore, complete treatment of agricultural runoff still needs additional process control and end treatment technologies. So, how to you deliver this to the public? Is it possible to produce crops with little to no impact on the environment? And, most importantly, is it sustainable for a business?
Increasingly, consumers are looking toward biopesticide use.
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