Inputs for sustainable crop management
By Ross H. McKenzie PhD P.Ag.
Direct seeding has contributed to sustainable crop production. Photo by Bruce Barker.
Optimum crop production depends on inputs of commercial fertilizer, livestock manure, herbicides, fungicides and insecticides. The economic benefits of increased crop production have been very positive; however, we must also recognize potential negative ecological effects of fertilizers and pesticides.
Commercial fertilizers and livestock manure are used to increase crop yields and to replace soil nutrients removed by harvested crops. Fertilizer and manure have been essential in reversing the trend of declining soil productivity and declining soil nutrient reserves. Research across Western Canada has clearly shown that added fertilizer not only increases crop yields, but also leads to increased soil organic matter when more crop residue and root matter are returned to the soil.
With the use of fertilizers, manure and pesticides comes the increasing environmental concern over potential contamination of soils, surface water and groundwater, and even air quality. A number of new and ongoing research studies by provincial agriculture departments, universities and Agriculture and Agri-Food Canada are being conducted across Western Canada to better understand various concerns.
A number of important lessons have already been learned from research. With practical knowledge, producers can take a very proactive approach to ensure agricultural practices minimize negative effects when utilizing input products on their farms.
Nitrogen and nitrates
Nitrogen (N) in various fertilizers and livestock manure is converted by soil microbes to nitrate-nitrogen (NO3-N), the primary form of N that plants take up. Nitrate is negatively charged and is not held by negatively charged soil particles. Therefore, higher levels of nitrate in soil coupled with excess rainfall or irrigation can result in leaching of nitrate through the soil root zone and into groundwater.
Some ways to minimize the potential for nitrate leaching include:
- Soil test to determine soil nitrate-nitrogen levels; then, use the information to determine the optimum N fertilizer and/or manure application rates. Select a realistic target crop yield and apply the N to meet (similar to average) crop requirements.
- Take all sources of N into account, including N from previous manure applications, N in crop residue, N mineralization potential of your soil, and previous pulse or legume crops.
- Areas in a field that have uniquely different soil types may require different fertilizer management practices or application rates. These unique areas should also be soil sampled separately from the rest of the field and managed separately.
- Optimize N fertilizer application method and timing:
- Band or side-band N fertilizer instead of broadcast incorporation to maximize crop efficiency of uptake and minimize N fertilizer losses for annual crops.
- Apply split N fertilizer applications on hay and pasture land.
- Apply split N fertilizer applications for longer-season irrigated crops grown on sandy soils using fertigation (fertilizing through the irrigation system).
- When manure or N fertilizer is applied in fall, wait until late fall when surface soil temperature is less than 7 C to slow the release of N to the mobile nitrate form.
- Consider the use of new, slow release N fertilizer products to minimize the amount of nitrate-nitrogen in the soil and minimize N leaching potential.
Shift to direct seeding
The shift to direct seeding to minimize soil disturbance and maintain as much crop residue cover as possible on the soil surface has a number of sustainable benefits to producers and the environment:
- Reduced soil disturbance results in less rapid soil organic matter breakdown, resulting in increased soil organic matter levels and improved soil structure, leading to improved soil quality.
- Placing fertilizer with the seed and in a band at seeding puts the fertilizer well below the soil surface, which greatly minimizes potential nutrient runoff from fields into surface water.
- Improved soil organic matter levels and improved soil structure result in reduced soil moisture loss and increased water infiltration rate, which reduced water runoff into surface water.
- Improved soil moisture conditions will reduce the need for land to be summerfallowed. Summerfallowed land has a higher risk of nitrate leaching, a higher occurrence of soil salinity and a greater risk of soil erosion.
- Weed seeds are less likely to germinate and grow on the undisturbed soil surface, reducing annual weed problems and potentially reducing the need for some herbicides.
- Less fuel is needed for field operations with direct seeding, which reduces greenhouse gas emissions and is cost saving for the producer.
- Continual soil cover protects soil from wind and water erosion, which greatly reduces the risk of soil and nutrient movement into surface waters.
Effective use of sustainable crop rotations
The use of diverse crop rotations can be beneficial to combat some weeds, crop diseases and insects. Growing a range of cereal, oilseed, pulse and/or forage crops will result in the use of a wider range of herbicides from different groups, which will reduce the potential development of herbicide-resistant weeds.
Diverse rotations with different crops can disturb weed populations to help keep weed populations in check. Some diseases and insect pests can also be kept in check with more diverse crop rotations.
Always avoid growing the same crop two years in a row on the same land to minimize pest problems and reduce the need for repeated use of the same crop protection chemicals (herbicides, fungicides and insecticides).
The inclusion of legumes in the crop rotation will reduce the need for N fertilizer. The N-fixing ability of legumes generally means that little or no N fertilizer is needed for crops such as alfalfa, sweet clover, pea, chickpea, bean and lentil. In the year following an annual legume, plant-available N is added to the soil as residue breaks down, reducing the need for commercial N fertilizer. Further, N from residue is released slowly over the next growing season; therefore, there may be less risk of nitrate accumulation in soil, which may reduce the risk of nitrate leaching.
Reduced N fertilizer requirements will reduce the amount of energy needed to manufacture and transport N fertilizer to the farm, thereby reducing greenhouse gases and conserving energy.
Use livestock manure wisely
Livestock manure is an excellent fertilizer and must be viewed and managed as a resource rather than a waste:
- Soil testing is critically important to allow for good nutrient management planning. By determining nutrient levels in soil, producers can better match nutrient levels in manure and balance them with crop nutrient requirements. This practice will lead to reduced problems of nutrients entering surface or groundwater.
- When applying manure, always stay a safe distance away from surface water bodies.
There is increasing concern about phosphorus (P) from agricultural lands causing problems with surface water contamination. Phosphate leaching into groundwater is rarely an issue as inorganic soil P is normally not mobile in soil and normally does not leach significantly. However, inorganic and organic P can be carried with sediments into surface water. Water runoff from agricultural lands is a serious environmental problem. Ensuring that water erosion does not occur on farms will go a long way toward minimizing contamination of surface waters. The shift to direct seeding has played a strong role in minimizing soil erosion and movement of sediments into surface waters.
Pesticides in surface waters are of increasing concern, and routine monitoring of surface waters over the past 15 years for pesticides has indicated there are significant problems in Alberta. Fortunately, most detected herbicides have been below the current water quality guidelines for aquatic life and drinking water. But this is an issue of serious concern.
It is thought that the primary means of herbicide transport into surface waters is by water movement of sediments from fields and in some situations transport of soil particles by wind. Soil conservation efforts, such as reduced tillage and direct seeding, can go a long way toward minimizing this transport mechanism. When using soil-applied herbicides, maintain good trash cover to minimize soil erosion and water runoff from fields.
Leaching of herbicides into shallow groundwater has been identified as a potential concern, particularly on sandy soils in higher rainfall areas and on irrigated land. Leaching will occur when excess water moves through the soil before herbicide breakdown has occurred. Herbicides with the greatest risk of leaching have a higher solubility and have a longer half-life (resistant to rapid breakdown).
To minimize herbicide leaching, producers should pay particular attention to herbicide solubility and the rate of breakdown (half-life) of the herbicides they use. Select herbicides with lower solubility when farming on sandier soils with higher leaching potential. To avoid pesticide contamination of water at point source, producers should use a nurse tank to fill a sprayer to avoid the problem of back-siphoning from a sprayer tank into a water source. Herbicide spills during tank fill can also contaminate water sources. To prevent this potential problem, add the concentrated pesticide product to the spray tank at a safe distance away from a water source.
Fungicide and insecticide use have increased dramatically across the Prairies in the past decade. Repeated use will lead to greater pesticide resistant diseases and insects. There are questions and concerns about potential negative effects of fungicides on soil microorganisms. There is increasing concern with the negative effects of insecticides on beneficial insects. When we use crop protection chemicals, we must consider the potential negative effects on our soils and the ecosystem in which we live.
It is critically important that our agricultural cropping systems be complementary to maintain healthy, productive ecosystems, which are also essential to human well-being. This article is intended to stimulate thought and discussion concerning how agricultural cropping practices can be made more sustainable. With continued research and development of practical knowledge, Prairie producers can continue to take a very proactive approach to minimize potential negative effects of our industry when utilizing fertilizers and pesticides on their farms.
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