Optimum crop production depends on inputs of commercial fertilizer and herbicides. Technology-based practices have increased food production across the prairies. While the economic benefits of increased production have been generally very positive, the ecological impacts have not always been as positive.
"Commercial fertilizers and animal manure are used to increase crop yields and to replace soil nutrients removed with harvested crops," says Dr. Ross McKenzie, research scientist - agronomy with Alberta Agriculture and Rural Development, Lethbridge. "Both have been valuable in reversing the trend of declining soil productivity and soil nutrients. Research across Western Canada has clearly shown that added fertilizer not only increases crop yields but also builds soil organic matter when more crop residue and root matter is returned to the soil."
Managing and using inputs
Management and use of fertilizers, manure and pesticides vary widely across Alberta due to the wide range of soil and climatic conditions. For example, in the Brown Soil Zone, located in south eastern Alberta, the average growing season precipitation is about 125 to150 mm, and the area has a high evapotranspiration potential and longer growing season. In the Dark Brown Soil Zone, the average growing season precipitation is about 175 to 200 mm with moderately high evapotranspiration potential. In the Black Soil Zone, located in central Alberta, the average annual precipitation is approximately 250 mm with moderately low evapotranspiration potential. In the Gray Wooded Soil Zone, located primarily in north central and northern Alberta, the average annual precipitation is approximately 150 to 200 mm with a lower evapotranspiration potential and shorter growing season.
"With the use of fertilizers, livestock manure and herbicides comes the increasing environmental concern over potential contamination of soils, surface water and groundwater," says McKenzie. "A number of new and on-going research studies that address some of these concerns are being conducted across Alberta by Alberta Agriculture and Rural Development, and Agriculture and Agri-Food Canada.
"A number of important lessons have been learned from previous and on-going research across Alberta. With practical knowledge, farmers can take a very pro-active approach now to minimize the potential negative effects when utilizing fertilizers, various manure types and pesticides on their farms."
Nitrogen in various fertilizers and manure are converted by soil microbes to nitrate-nitrogen (NO3-N), the form that plants take up. Nitrate is negatively charged and is not held by soil particles. Therefore, higher levels of nitrate in soil, combined with excess rainfall or irrigation, can result in leaching through the soil root zone into groundwater. High nitrates in soil occur when manure or commercial fertilizers are applied in spring before significant crop uptake has occurred during the growing season or when these are applied at rates greater than crops require. Some of the suggested 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 nitrogen fertilizer and/or manure application rates
- select a realistic target crop yield and apply the nitrogen to meet crop requirements
- take all sources of nitrogen into account, including nitrogen from previous manure applications, N in crop residue, and previous pulse crop or legume plowdown
- areas of each field that have uniquely different soil types or management history may require different fertilizer management, so they should also be soil sampled separately from the rest of the field and also managed separately
Optimize nitrogen application method and timing by:
- band or side-band N fertilizer instead of broadcast-incorporation to maximize crop efficiency of uptake and minimize N fertilizer losses
- 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
- when manure or N fertilizer is applied in fall, wait until late fall when surface soil temperature is less than 7ºC
- consider the use of new slow release N fertilizer products to minimize the amount of nitrate-nitrogen in the soil
Direct seeding protects soil surface
"The shift to direct seeding can help minimize soil disturbance and maintain significant crop residue cover," says McKenzie. "Maintaining residue cover for as long as possible on the soil surface has a number of sustainable benefits to farmers and the environment, one being that the reduced soil disturbance results in less rapid soil organic matter breakdown, resulting in increased soil organic matter levels and improved soil structure, which lead to improved soil quality."
Improved soil organic matter levels and improved soil structure result in reduced soil moisture loss and increased water infiltration rate, therefore reducing surface runoff of water. These improved soil moisture conditions can reduce the need for land to be summerfallowed. Summerfallowed land has a higher risk of nitrate leaching, 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 the annual weed problems, and potentially will reduce the need for herbicides," says McKenzie. "Continual soil cover protects soil from wind and water erosion. This management practice greatly reduces the risk of soil and nutrient movement into surface waters. Also, less fuel is needed for field operations, which reduce greenhouse gas emissions and is a cost saving for the farmer."
Use of diverse crop rotations can be beneficial to combat some weeds, crop diseases and insects. Growing a range of cereal, oilseed, pulse and forage crops will result in use of a wide range of herbicides from different groups which will reduce to potential for herbicide resistant weeds to develop. Diverse rotations with different crops can disrupt weed populations to assist in keeping weed populations in check. Some diseases and insect pests can be kept in check with diverse crop rotations. Always avoid growing the same crop two years in a row to minimize pest problems and reduce the need for crop protection chemicals (herbicides, fungicides, insecticides).
The inclusion of legumes in the crop rotation will reduce the need for nitrogen fertilizer application. The nitrogen fixing ability of legumes generally means that no N fertilizer is needed for crops such as alfalfa, sweet clover, pea, chickpea and lentil. In the year following a pulse crop (annual grain legume crop), plant-available nitrogen is added to the soil as legume residues breakdown, reducing or even eliminating the need of N fertilizer. The N from the legume residue is released slowly over the next growing season, therefore there is less risk that nitrate will accumulate, which can reduce the risk of nitrate leaching. Reduced N fertilizer requirements will reduce the amount of energy needed to manufacture and transport the fertilizer to the farm, thereby reducing greenhouse gases and conserve energy.
Managing the manure resource
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 good nutrient management planning," says Dr. Ross McKenzie, research scientist - agronomy with Alberta Agriculture and Rural Development, Lethbridge. "Once nutrient levels in soil are determined, nutrient levels in manure can be matched and balanced with crop nutrient requirements. This will lead to reduced problems of nutrients entering surface and groundwater."
When applying manure, always stay a safe distance from surface water bodies and use conservative rates of manure application to avoid leaching and runoff problems.
"There is increasing concern about phosphorus (P) from agricultural lands causing problems with water contamination," says McKenzie. "Phosphate leaching into groundwater is rarely a problem as P is normally not mobile in soil and does not leach. Generally, P is attached to soil particles and other soil elements such as calcium, iron and aluminum. However, P can be carried to surface water with sediments into surface water."
Ensuring that water and wind erosion do not occur on farms will go a long way to minimize contamination of surface waters in Alberta. The shift to direct seeding has played a strong role in minimizing soil erosion and movement of sediments into surface waters in Alberta.
"Pesticides in surface waters in Alberta are also of increasing concern and routine monitoring of surface waters over the past 15 years for pesticides has indicated that there are problems," says McKenzie. "Fortunately, most detected herbicides have been below the current water quality guidelines for aquatic life and drinking water."
It is thought that the primary means of herbicide transport into surface waters is by wind and water movement of sediments from fields. Soil conservation efforts, such as reduced tillage and direct seeding can go a long way to minimize this transport mechanism. When using soil applied herbicides in the fall, keep a good trash cover to minimize soil erosion and water runoff from fields.
Leaching of herbicides into shallow groundwater has been identified as a concern 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 are soluble and have a longer half life (resist breakdown).
To minimize herbicide leaching, farmers should pay particular attention to herbicide solubility and rate of breakdown. When selecting herbicides:
To avoid pesticide contamination of water at point source, the use of a nurse tank to fill a sprayer is strongly advised. Using a nurse tank will avoid 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 at a distance from the water source.
- consult the Alberta Agriculture Crop Protection book (Agdex 606-1, commonly called the Blue Book) to select herbicides with lower solubilities and more rapid breakdown
- select herbicides with lower solubility when farming on sandier soils with higher leaching potential, on irrigated land or soils in higher rainfall areas
Crop Protection 2008, the Blue Book is available from Alberta Agriculture's Publication Office, 7000 - 113 Street, Edmonton, AB T6H 5T6, by calling toll-free 1-800-292-5697 or calling toll-free in Alberta 310-FARM (3276). The guide can also be ordered online at www.agriculture.alberta.ca/publications. The cost of the Blue Book is $12, plus GST, plus shipping and handling.
"These tips are intended to stimulate thought and discussion concerning how agricultural cropping practices using commercial fertilizers, livestock manure and pesticides can be made more sustainable for food production and protect the environment for many generations," says McKenzie. "With continued research and development of practical knowledge, Alberta farmers can continue to take a very pro-active approach to minimize the potential negative effects when utilizing fertilizers, various types of manure and pesticides on their farms.
"While runoff from agricultural lands can be a serious potential problem, it must be remembered that contamination of surface water from urban waste and runoff is also a very serious concern. It is critically important that all Alberta's, both urban and rural, work together to maintain healthy productive ecosystems that are essential to human well-being."