Nutrient Management Issues for 2019 March 29, 2019
The impact on soil nutrient availability of the March snowmelt/heavy rainfall event is highly variable. The following describes what to consider in areas of little, moderate, and severe harmful effects.
Minimal Harmful Effect
There was little harmful effect on soil nutrient availability for most cropland and grassland. There may have been more sheet and rill erosion and movement of crop residue than normal. Following are considerations for areas with little harmful effect.
- To prevent soil compaction, avoid traffic in the field while the soil is still wet. In many areas growers were not able to make fall N applications and may be feeling some urgency to make spring applications; however, delay applications until the soil dries to minimize compaction. Applying N after planting is an option.
- Some application of fertilizer or manure P and lime on frozen soil occurred in January and February. These certainly are not good agronomic practices! It is likely that much of this was lost in runoff with significant water contamination. If you are concerned about applied P runoff, sample the 0-8 inch soil depth and base fertilizer use decisions on the soil test results. (See Guidelines for Soil Sampling, NebGuide G1740).
- There will be an urgency to apply fertilizer N to pastures and to winter wheat before jointing. Avoid applications in wet fields where the traffic could cause soil compaction. Consider the potential volatilization loss for urea-based fertilizers applied on wet soils.
- Many feedlot holding ponds need to be pumped, usually with pivot irrigation. If possible, try to delay applications until soil conditions are drier. The effluent may have higher nutrient content than normal and should be tested so nutrients can be properly credited.
- Land application of spoiled grain or forage may be done, with these considerations:
- Credit the likely amount of N available. Assume 35% of grain N will be available (26 lb/t for corn and 130 lb/t for soybean on a dry weight basis); however, it won’t be available until later in the season. Apply 60 lb of fertilizer N near planting and then do an in-season assessment to determine if a side-dress N application is needed such as with a pre-sidedress nitrate test or remote sensing of corn crop canopy greenness.
- The spoiled material may be toxic to livestock and wildlife and needs to be thoroughly incorporated, preferably within 24 hours of application.
- Spoiled grain is likely to be mixed with some that is still viable and will germinate, leading to volunteer growth, often of glyphosate-tolerant corn or soybean.
- Composting spoiled feed and applying it later may be the better option. (See Composting Manure and Other Organic Materials, NebGuide G1315).
Moderate Harmful Effect
Moderate effects occurred with some ephemeral gully formation, especially in unprotected waterways and where there was standing water for a few days. Some low-lying areas have excessive sediment and debris deposition or erosion. It appears most of these areas will be planted this year, although planting may be delayed.
- Extra fertilizer may be needed where gullies are filled. Sample the soil and base application amounts on soil test results.
- Again, avoid traffic on wet soil.
- Fall-applied N should still be in ammonium form if it was applied when the soil temperature was below 50°F and microbial activity was very low. It is not subject to leaching at this time; however, if the soil has thawed enough to allow soil water infiltration and percolation, soil water may be at field capacity. In May there will be much potential for leaching of nitrate-N when the soil becomes warm enough to allow ammonium-N conversion to nitrate-N.
- Residual soil nitrate-N from 2018 is already subject to leaching. On average, approximately 60 lb N/ac of residual soil nitrate-N is available annually in the upper 4-feet of soil.
- The 0-2 foot soil depth should be sampled to determine the amount of nitrate-N in the soil. This N should be credited in determining N application rates.
- At this time N loss to denitrification would not be significant as there is little microbial activity in cold soil. If water-logging occurs in May or June when the soil is warmer, loss of soil nitrate-N to denitrification may be as much as 5% of applied fertilizer N per week of water saturation.
- With very wet fields that can be planted in 2019, split your N application with at least 50% applied in-season based on an N availability assessment. (See No. 5a under Minimal Effect).
- Sediment and debris deposition. How much of the deposition is near soil-like, sand, and crop residue? How uniformly distributed is the sediment? Will leveling or removal be needed? The answers vary by field. In some fields, even trees were deposited.
- If more than 2 inches of soil was lost or deposition was more than 2 inches deep, extra fertilizer will likely be needed. Rates should be based on soil sampling this spring for the 0-8 inch depth.
- With sedimentation of more than 3 inches or erosive cutting of soil of more than 3 inches, or if water stands for more than two weeks, seed for the next soybean crop should be inoculated with bradyrhizobia.
- Fertilizer application in excess of UNL recommendations is not justified for short- or long-term benefits. (See Nutrient Management for Agronomic Crops in Nebraska.)
- Prolonged waterlogging may kill alfalfa. If this happens, plant corn in the field in 2019 if possible. Flood water may have brought contaminants into the field which may make perennial forage unsuitable for feeding.
Severe Harmful Effect
Generally, it is too early to assess the damage, estimate recovery, and suggest nutrient management practices. If a commercial crop is not planted in 2019, plant a cover crop as soon as it is dry enough. A warm-season cover crop might be used if planted before August or a cool-season crop might be planted in August or later. The cover crop may help to revive dormant soil microbes and restore productivity, prevent erosion and leaching, and suppress weeds.