Nutrient Management – Crops

What are nutrients?

Nutrients are naturally occurring elements in soils that support plant growth. Prairie crops require 17 nutrients, but the most important are nitrogen and phosphorus. These two nutrients are often added to the soil through fertilizers and manure in modern crop production. While relatively large amounts of nitrogen and phosphorus are needed to sustain crop production, over-applying these nutrients can have negative consequences for local and regional water supplies.

What is runoff?

Runoff is any excess water which saturated soils can’t absorb. In the prairies, runoff is primarily tied to spring melt, when large amounts of surface water drain off flooded fields. Spring runoff isn’t just water, though; it includes all the materials and nutrients the snow retained through the winter. That means prairie farms can lose key crop-growing nutrients like nitrogen and phosphorus during spring snowmelt events.

Why should I be aware of nutrients and runoff?

Runoff from storms and snowmelt can wash nutrients into water supplies, where they end up fertilizing lakes and wetlands instead of fertilizing your crops. The algae blooms affecting Lake Winnipeg and other prairie lakes, for example, are largely caused by nutrient runoff from farms. This excess of nutrients — called eutrophication — encourages algae blooms, which are unsightly and hazardous. Eutrophication can suffocate fish and trigger toxic effects in the water.

Lakes are incredibly sensitive to fertilizer inputs. Though producers manage fertilizer by the kilogram, lakes can respond to microgram-level increases, akin to drops of water in an Olympic-sized swimming pool. To maintain or improve our water quality, we need to minimize nutrient losses from fields as much as possible. In regions with intensive livestock production, nutrients need to be managed with additional care because repeated manure application can pool nutrients in the soil, creating a long-term source of nutrient loss.

Why is effective nutrient management crucial in the prairies?

  • First, our climate and landscape can make it challenging to keep nutrients on fields. Crop growing season is short in the prairies. When snow accumulates on fields, nutrients can dissolve into the snow and wash away in spring. Snowmelt is a key source of runoff and a critical period of nutrient transport on the prairies. Unfortunately, many beneficial management practices developed for warm conditions or soil erosion control do not work at full capacity with prairie climate and landscape.
  • Second, our lakes are highly vulnerable to nutrients. Prairie lakes are often shallow, with large watersheds encompassing agricultural land. These factors can make prairie lakes even more vulnerable to nutrient pollution and algae blooms.
  • Third, some management practices — such as reduced tillage and bale grazing — can build up nutrients on the soil surface and thus increase nutrient export with snowmelt runoff. As a result, we must act to minimize nutrient transport if we want to help address growing problems in our prairie lakes.

What can I do about nutrients?

Nutrient management is a challenge. Producers need to apply large quantities of phosphorus and nitrogen to support crop growth, but just a small amount in water can cause environmental consequences. Here are some things to consider to protect water quality in the prairies.

Follow 4R principles: Fertilizers and manures should be applied following the 4R principles, i.e., applying nutrients at right rate and right timing, using the right source and right placement method.

Match applications to crop requirements: Over-applying nutrients can increase nutrient loss during runoff. Likewise, surplus nutrients can build up nutrient pools in soils and contribute to long-term nutrient loss. Soil tests are a valuable tool to determine nutrient application rates and recommendations.

Avoid nutrient application in winter and on snow-covered or frozen ground: The majority of runoff in Saskatchewan — and the majority of nutrient loss — is part of winter snowmelt.  If fertilizers are on fields late in the season, key nutrients are likely to wash away in spring. If possible, avoid winter application, or target winter manure to low-risk fields that won’t drain into local streams.

Be aware that nutrient chemistry varies with sources: Fertilizer and manure applications can affect soil pH and eventually alter soil chemistry. In manured cropping systems, nitrogen-based manure applications (i.e. applying manure at rates to meet crop nitrogen requirements) often lead to surplus phosphorus in soil.

Increase fertilizer injection: Phosphorus runoff is tied to interaction with snowmelt. Another option for reducing nutrient runoff, then, is injecting fertilizer and manure into the soil to minimize contact with snow. This must be done before the ground freezes

Avoid nutrient accumulation in surface soils and draw down soil nutrients when they are high:  Continuous use of minimum- or zero-till practices — also known as conservation tillage — can stratify nutrients at the soil surface. This stratification increases when surface fertilizers are applied without tillage. Stratification increases the risk of nutrient loss at the surface and reduces the amount of nutrients available at the root system. If your soil test shows high nutrients, you can draw down those numbers by reducing nutrient inputs while removing crop harvests.

Consider implementing a test strip: Test strips can determine your soil’s nutrient needs. Lower your fertilizer application rate on a designated strip of your field and see if it affects crop growth. If the test strip crop grows the same as everything else, you know that you didn’t need the extra fertilizer that was applied on the rest of the field. This can help you make decisions about future fertilizer rates.

Remember vegetation is also a nutrient source: Forages, cover crops and crop residues contain considerable amounts of nutrients. A large proportion of the nutrients can be released from vegetation during the freeze-thaw cycle, so exercise caution with cover crops on the prairies. Depending on climate and soil conditions, the nutrients released during freezing winters may be re-utilized by crops, or may be washed off the fields by runoff.

Farm/watershed system-level management:

Drainage management: Connecting wetlands to waterways has effects far beyond the farm. Drainage reduces the storage capacity of your land, leading to more nutrient loss across a wider area. If you plan to drain, consider reducing your nutrient inputs to reduce the downstream impact. If possible, maintain or create water storage at low elevations on your land.

Target manure application to low-risk fields: Nutrients are a problem under two conditions: when nutrient levels are high, and when potential for runoff is high. Focus manure application on parts of your land that don’t drain to regional waterways to minimize effects of water quality.

Cycle manure (and nutrients) among area farms: The economics of agriculture creates a nutrient imbalance: crop producers become nutrient-poor as phosphorus and nitrogen are taken up by plants, and livestock producers become nutrient-rich as those plants are consumed by their animals in feed. This creates areas of nutrient deficits and surpluses. If possible, export excess manure to nearby farms with nutrient needs.

The takeaway:

Reducing nutrient loss is environmentally smart and economically sound. Implementing strategies to reduce nutrient loss will benefit water supplies and save on fertilizer expenses. Your local knowledge is vital. You know how water moves on your land, where nutrients might accumulate, and what strategies will work best in the context of your farm. By implementing one or more of these strategies, you can help reduce nutrient runoff and protect drinking water in your area.  Maintaining the lowest input you can, to sustain crop yields, will help water quality.


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