Managing nutrients in cold climates
Opportunities to avoid manure application during winter months can minimize losses and improve nutrient uptake. by Eric Young
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rop production in Northern regions is characterized by short growing seasons and seasonally high runoff potential. Soils warm slowly in the spring with extended periods of wetness, posing crop production and environmental risks. Nutrient use efficiency (NUE) is the relative amount of applied nutrient that ends up in a crop. It varies widely by crop, weather, fertilization methods, and others factors. Applying manure to actively growing crops (after hay cuttings or to cover crops, for example) or immediately prior to planting annual crops like corn can improve NUE and reduce losses. Methods of application also impact manure NUE. From an NUE standpoint, applying manure in late fall, winter, and early spring (often termed the nongrowing season) is not ideal. Soils are generally wetter with higher runoff potential and depressed soil biological activity. In addition, freeze-thaw transitions have a major impact on runoff potential and nutrient movement. Frozen soils allow minimal infiltration and can elevate dissolved phosphorus (P) mobility to surface water with rapid snow melting. Surface runoff and erosion processes drive both topsoil and P loss in many places. Mitigating surface runoff from field nutrient source areas is critical to maintain soil organic matter and crop productivity and for reducing nutrient runoff risk, particularly for farms
Control
8% solids
15.4% solids
Figure 1. Dairy manure applied at the same rate (2,852 gallons per acre) and source but at differing solids content spanning the range of liquid to semisolid manure. Small plots were used to isolate and measure snowmelt runoff. Pictures by Eric Young and Jessica Sherman. adhering to water quality regulations. Snowmelt accounts for a substantial amount of the annual water budget and surface runoff in cold climates. While manure application to frozen, saturated, or snow-covered soils is discouraged in general for agronomic and environmental reasons, manure is still routinely applied under a wide range of weather conditions, including close to the onset and during the nongrowing season. Many dairy operations have a limited number of fields that can reasonably receive manure and often have a need to fall-apply manure to fields with or without a cover crop. Fall-applied manure remains close to the soil surface where it is exposed to freezing temperatures followed by variable melting events as spring approaches. Manure nutrients in surface soil interact with melting snow, releasing nitrogen (N) and P. Applying manure to a growing crop (hayfield or cover crop) using low-distur-
16 | Journal of Nutrient Management | February 2020
F3 16-17 Q1 2020 Cold Climate.indd 2
5% solids
bance methods can reduce both soilbound and soluble nutrients. However, some level of nutrient runoff is inevitable, depending on the amount of runoff and soil N and P concentrations. Large storm events during the growing season can contribute to annual runoff losses, but losses during the nongrowing season are important to recognize in cold climates. Available surface area for sorption and other nutrient attenuation mechanisms are compromised in frozen or partially frozen soils. The how (what method, rate, and incorporation level) and when of manure application in relation to weather and soil conditions is a critical aspect of trying to better predict runoff nutrient loss risk from manure.
The manure matters, too While multiple field-related factors (soil type and drainage, hydrology, manure application method, crop system, and tillage intensity) affect jofnm.com
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