Use of Fertilizers, Manures and Pesticides for Sustainable Farm Management

Optimum crop production depends on inputs of commercial fertilizer and herbicides. Today’s technology-based agricultural practices have had a huge effect on increased food production across the prairies. Generally, the economic effects of increased production have been very positive; however, the ecological effects are not always as positive.

Commercial fertilizers and animal manure are used to increase crop yields and to replace soil nutrients removed with harvested crops. 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 are returned to the soil.

The management and use of fertilizers, manure and pesticides vary widely across Alberta due to the wide range of soil and climatic conditions. For example, the Brown soil zone has an average growing season precipitation of about 125 to150 mm, a high evapotranspiration potential and a fairly long 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, the average annual precipitation is approximately 250 mm, with moderately low evapotranspiration potential. In the Gray Wooded soil zone, 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. A number of new and ongoing research studies by Alberta Agriculture and Rural Development, and Agriculture and Agri-Food Canada are being conducted across Alberta to address various concerns.

A number of important lessons have been learned from previous and ongoing research across Alberta. With practical knowledge, producers can take a very proactive approach now to minimize the potential negative effects when utilizing fertilizers, various manure types and pesticides on their farms.

Nitrogen and Nitrates

Nitrogen (N) in various fertilizers and manure is 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 applied at rates greater than crops require. Some of the suggested ways to minimize the potential for nitrate leaching include the following:

• 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 (similar to average) 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. These unique areas should also be soil sampled separately from the rest of the field and managed separately.

• 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 irrigation equipment).
• When manure or N fertilizer is applied in fall, wait until late fall when surface soil temperature is < 7 C.
• Consider the use of new, slow release N fertilizer products to minimize the amount of nitrate-nitrogen in the soil.

• 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.
• 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.
• Improved soil moisture conditions can 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 herbicides.
• Less fuel is needed for field operations with direct seeding, which reduces greenhouse gas emissions and is a 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.

• Soil testing is critically important to allow good nutrient management planning. By determining nutrient levels in soil, producers can match nutrient levels in manure and balance them with crop nutrient requirements. This practice will lead to reduced problems of nutrients entering surface and groundwater.
• Use conservative rates of manure application to avoid leaching and runoff problems.
• When applying manure, always stay a safe distance away from surface water bodies.

• 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.