The concept of nutrient management is not new, as agricultural producers have always gone through some version of logically deciding the amount, source, placement, form and timing for nutrients delivered to their crops. It is to the farmer’s advantage to think this through and make good crop nutrition and soil fertility decisions, as crop productivity and farm profitability are impacted.
Through the 1990s to present, agricultural producers have been asked to formally document nutrient management plans to show that they are:
1. Matching crop nutrient need with soil nutrient content and the best combination of on-farm nutrient sources (rotated legume crops and livestock manure) and/or commercial fertilizer;
2. Correctly managing crop nutrition, soil fertility and nutrient applications so that productive, profitable crops receive and utilize nutrients and that excess nutrients are not applied to be lost from the root zone toward groundwater or from the top layers of the soil in surface water runoff.
What is involved?
Nutrient management plans typically contain six key things: soil test results, cropping information, manure spreader calibration information, nutrient crediting, a detailed manure application plan and a soil conservation plan.
Soil tests are possibly the most important part of a nutrient management plan. They can help you measure the current level of soil fertility, determine crop nutrient needs, and monitor changes in fields’ nutrient status over time. Soil tests should be current within the last four years to reflect changes in fertility over that time period.
One soil sample should be collected per five acres, and each sample sent to the lab should be a mixture of at least 10 soil cores from within the five-acre sampling area. A soil probe or auger should be used to sample at least six inches into the soil profile.
Crop strips should be sampled individually even when they are less than five acres in size, unless each strip has the same crop and management history. Soil samples collected should be representative of the entire field and avoid fencelines, low spots and fertilizer bands, which could lead to inaccurate recommendations.
Each sample should be labeled with your name, the field it came from and the sample number, and marking the location corresponding to each sample number on a map is also helpful.
Cropping information in a nutrient management plan includes a field’s history of rotations, fertilizer and manure applications, yield goals and tillage practices. One easy way to warehouse all of this information is through the use of a computer software program, called SNAP-Plus.
Once you enter your rotations, fertilizer and manure applications, yield goals and tillage practices, SNAP-Plus will supply the user with crop nutrient recommendations, soil erosion assessments, field phosphorus index values, and a rotational phosphorus balance.
Once you enter this information, it can be relatively easily changed to answer “what if” questions or reflect crop rotation or nutrient application changes, and has valuable potential in its recordkeeping capability.
Good recordkeeping has many advantages for a farm enterprise and the nutrient management planning process can give you those records for your soil fertility management – no matter what plan-writing tool you use.
Nutrient crediting means considering the nitrogen legumes have put into the soil, along with taking into account the nitrogen, phosphorus, potassium and sulfur in manure applications.
When taking legume credits, the amount of credits taken depends on soil texture (sands vs. others), harvest management (how tall was crop when plowed or killed) and stand density.
In the case of alfalfa, you can take 90 pounds of nitrogen credit for next year’s crop on even the poorest stands (unless the soil is sandy, then consider taking 40 pounds of nitrogen credit for next year’s crop).
When taking manure credits, you should know how much you spread through a manure spreader calibration, and it should be spread as evenly as possible across the entire field, even if it is spread a little bit at a time.
Manure spreader calibration is important so you know how many tons or gallons per acre you are spreading. This allows you to take credit for the amount of nutrients applied to the field and adjust fertilizer applications according to yield goals.
There are a number of methods to determine a manure spreader’s application rate. For liquid manure tankers, if you know the tank volume (3,000 gallons, for instance) and the number of tanker loads per acre (three) – the application rate is 9,000 gallons per acre.
For solid manure spreaders, the methodology is similar – though it is usually more accurate to use portable weigh scales and a measuring wheel to determine the spreader’s capacity.
County extension and land conservation offices often have resources (scales and measuring wheels) and other helpful methods to help you determine this critical fertility management number.
A manure spreading plan helps pinpoint fields that need the nutrients for next year’s crop. It also helps a farmer designate the right time for applying manure onto each field. Discovery Farms data shows that runoff is more likely in February and March than in early winter.
Whether spreading liquid or solid manure, the shorter the time between an application and a runoff event, the greater potential for nutrient losses.
Frozen and snow-covered ground can contribute a significant amount of nutrient losses if not managed carefully. Soils with high moisture content, such as after precipitation or snowmelt, should also be managed carefully to avoid losses.
Important considerations for manure applications when the soil is in this condition are the amount of water in the manure to be applied and the weather forecast. A detailed spreading plan can help you outline which fields are at a high, medium and low risk for runoff and when those time periods are for each field.
Another component of the spreading plan is identification of alternatives to spreading during high-risk periods, including temporary stacking areas.
A soil conservation plan has six parts and can be completed in cooperation with your local land conservation department. The components of the soil conservation include: actual versus tolerable soil loss for each field, crop rotation, percentage of slope for each field, the percentage of residue on a field and the tillage actions, soil maps, and aerial photos of fields.
Contact your county land conservation or extension office to find further information on nutrient management planning for your operation. PD
References omitted due to space but are available upon request.
—Excerpts from University of Wisconsin Pioneering Discoveries newsletter, Vol. 2, Issue 4, winter 2010 – 2011
Dennis Frame
Professor
University of Wisconsin – Extension
drframe@wisc.edu
