How much soil is moving, what can it cost farmers? – AgFax

Two ongoing studies measure how much soil is spread in different fields and how much nutrients lost by wind erosion can cost farmers.

Wind erosion

Sometimes you can see the soil coming out of your field, being washed away in the spring into ditches or blowing across roads and falling through the windows of houses. Other times it’s more subtle and slow. Most hilly fields have inflorescences with lighter soil due to prolonged wind, water and tillage erosion.

In addition to nutrient losses on the farm, sludge destroyed by wind can cause traffic accidents, increase breathing problems and change the movement of water through the landscape. When snow covers mix with dust, they absorb more sunlight and melt earlier.

Technically wind erosion is defined as the transfer of soil particles from one place to another, and this easily occurs where the soil is bare, loose and dry. It is difficult to measure where the soil comes from and where it is deposited. Many different factors, such as soil moisture, organic matter, resilience of aggregates, topography, surface cover and so on, cause wind erosion to behave erratically from one field to another and even in one field.

Depending on the size of the particles (sand, silt or clay), wind speed and power, the transport of the particles changes as the soil rises from ground level to atmospheric level. Small soil particles removed from the soil surface by wind can travel hundreds of miles.

For example, each year the dust removed from the Sahara Desert in North Africa travels more than 6,000 miles across the Atlantic Ocean and reaches the United States. Long-distance transport of dust is estimated using models, but ground-level wind erosion measurements are required to construct and test models.

Measurement methods

Dust collectors or traps such as the Big Spring Number Eight (BSNE) and the Modified Wilson and Cooke (WMAC) catch wind-borne precipitation with masts located at different heights to get a sense of the vertical distribution of sludge carried by the wind. Network mats located on the ground, assess the movement of sediments by wind or water on the soil surface. Both mats and dust collectors measure the movement of sludge in a given medium, but cannot confirm sludge loss.

At the boundary of field monitoring, a runoff can be recorded that actually leaves the farm field (although part of it could have been displaced from other locations). Sampling in ditches also provides an estimate of losses, but cannot confirm the origin of the deposits.

Two ongoing research projects

The first project: In 2021, we began considering the movement of spring sediments in Murray County in southwestern Minnesota. A corn / soybean farmer received a grant from the Minnesota Department of Agriculture to evaluate different tillage methods for yield, economy, and erosion. We used erosion mats to measure the sludge moving across the field surface between the corn planting and the first application of the herbicide.

Treatments (strip processing versus field processing) were applied in 60-foot repetitive strips, and five mats were used in each of the three locations across the field. Our first data showed that more sludge moves in strips cultivated in fields, with significant levels of nutrients in mobile sludge.

Strip-till Field
Precipitation movement (pounds / acre) 449 (± 328) 1074 (± 1148)
Nitrates (mg / kg) * 51.59 51.59
Phosphorus (mg / kg) * 36.2 36.2
Potassium (mg / kg) * 182.4 182.4

* Note that the samples were too small to estimate the nutrient content separately for each treatment. Phosphorus was measured by the Bray method.

Project two: During the winter of 2020-2021, wind-blown sludge was collected in small boxes (BSNE samplers) mounted on one foot above the ground. We housed two collectors on each of four 40-acre fields in Walsh County in northeastern North Dakota, a demonstration of conservation funded by General Mills. The fields differed in tillage (anti-unemployment treatment) and crop rotations (after edible beans against wheat).

In this case, tillage did not affect the amount of sediment movement, but the previous culture had a huge effect. Edible beans leave minimal sediment on the ground, and much more sediment moves through these fields. If you extrapolate the measured sediments along a one-mile stretch of road, one foot off the ground, we assume that these systems can move up to 160 pounds of sediment per day per mile.

Again, the sludge blows with a high content of nutrients and organic matter. When all this nitrogen (N), phosphorus (P) and potassium (K) left the field between November and April, this sediment cost up to $ 40 (December 2021 price: $ 0.951 / lb N, $ 0.918 / lb P, $ 0.665 / lb) K).

loss of wheat sludge against edible beans

Click Image to enlarge

Edible beans Wheat
Organic matter 5.2% 6.9%
Total nitrogen 0.23% 0.29%
Phosphorus (mg / kg) * 28.5 31.5
Potassium (mg / kg) 500 351
The value of nutrients (exhalation in miles 1 foot high, November-April) $ 40 $ 8

* Phosphorus was measured by the Bray method.

Overall, these preliminary data show that management makes a difference: leaving residues in the field or planting cover crops, as well as less aggressive tillage can slow down soil movement, saving more nutrients for the next crop. One thing we know from the edge is field monitoring, by Discovery Farms programs in Minnesota and Wisconsin and Root River Field to Stream Partnership in southeastern Minnesota is that erosion is bright – several events can have a big impact on overall soil movement.

Therefore, these preliminary data should not be taken as national averages. We will continue to collect data on these sites and add more reliable data on wind erosion in sugar beet fields, which are particularly vulnerable to winter erosion due to low residual cover and intensive tillage after beet harvesting.

We will use BSNE masts to measure rainfall movement at different altitudes, comparing fields with cover crops sown after beet harvesting, with fields without cover crops. After harvesting beets in cover crops there is a short time to grow, so we will see if they provide enough residue to slow down the loss of sludge and nutrients. How much soil is moving, what can it cost farmers? – AgFax

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