September 16, 2016

Applying Lime and Fertilizer in the Fall​

 

Key Points

  • Analysis of soil samples taken after harvest or the previous spring should guide your fall fertilizer applications.
  • Fall is the best time to apply any lime needed to neutralize soil acidity and improve nutrient availability.  
  • Review and follow local guidelines for fertilizer and manure applications to facilitate nutrient availability to the crop and to avoid fertilizer loss.

Soil Sampling Timing

The best time to collect soil samples for determining lime application is after harvest in the fall. However, it can be a challenge to collect soil samples at that time and have the results available for fall fertilizer applications. As an alternative, university Extension or soil testing laboratories can make fall fertilizer recommendations from soil samples collected the previous spring as long the recently harvested crop's nutrient removal is considered. Soil samples should be taken at least every four years, while following good sampling techniques recommended by your local university Extension office.

Applying Lime

A soil pH between 6.0 and 7.0 is generally the recommended range where plant nutrients are most available. Lime neutralizes soil acidity and adds calcium, a micronutrient essential to plant growth. Lime takes time to dissolve in the soil and neutralize acidity; therefore it should be applied about 3 to 6 months before planting crops. Applying in the fall provides plenty of time for the lime to dissolve in the soil profile before the next growing season. Lime should be applied and incorporated a month or more before adding fertilizers, since it can interfere with the availability of other nutrients, especially phosphorus. You should pay particular attention to the different sources of liming material. Differences among products in their neutralizing efficiency (calcium carbonate equivalent and particle size) will influence optimum application rates.

 

Phosphorus and Potassium Application

Reduced workload, dry soils, fertilizer availability, and the opportunity to spread fertilizer before tillage make fall an opportune time to apply phosphorus (P) and potassium (K). There are also good environmental reasons to apply P in the fall, since there is generally a lower risk of P runoff with typical fall weather and soil conditions. However, P and K fertilizer should not be applied on frozen ground, because applications made to fields with any slope can result in significant runoff and fertilizer loss.

Follow soil test recommendations to maintain P and K above their critical levels in the soil which can help supply adequate quantities of nutrients and support healthy plant growth. Allowing low soil test levels of P and K can result in lost yield potential, especially with K. If soil tests show P and K to be above the critical levels, you can save money by making no additional fertilizer applications for the next crop. Many farmers apply sufficient P and K to supply the necessary nutrients for two years of crop production. In a corn-soybean rotation, all of the K can be applied in the fall after soybean harvest, ahead of corn. Enough K will be returned to the soil from the corn residue for the following soybean crop. However, recommended fertilizer rates should be applied annually to soils that have low levels of P and K. These annual applications include P and K soil build-up and crop removal needs.

 

Applying Nitrogen

Reduced soil compaction, spreading out the workload, and potentially lower fertilizer costs are several advantages you may gain from applying nitrogen (N) in the fall. Potential disadvantages include the loss of N between application and crop use and potential environmental concerns from nitrates leaching into streams, lakes, and groundwater.

Fertilizers comprised predominantly of ammonium-N are preferred for fall application. N sources containing urea and/or nitrates have greater potential to be lost via leaching, volatilization, or runoff. Nitrate-N is subject to loss via leaching and denitrification while ammonium-N is relatively stable as it attaches to soil particles. Due to these concerns, anhydrous ammonia is a good source for fall-applied N.

Anhydrous ammonia should be applied in late fall, after soils cool to 50 °F, and continued cool weather is in the forecast (Figure 1). It is best to avoid sandy soils and poorly drained soils. Fall applications of N are generally feasible only in areas where low winter soil temperatures hinder nitrification of ammonium. It should not be applied in areas where soils seldom or never freeze or where there is a long period between the time they reach 50 °F and when they freeze. Nitrifying organisms (convert ammonium to nitrates) continue to function down to 32 °F, but at a slower rate. Long periods of time at low soil temperatures above 32 °F can still result in nitrification of a large percentage of fall-applied N. A nitrification inhibitor should be considered to slow the conversion of ammonium to nitrates and help improve the effectiveness of fall-applied N.

 
Figure 1. Anhydrous ammonia should be applied in late fall after soils cool to 50 °F.

 

 

Consideration should also be given to splitting N applications between fall and spring, rather than applying it all in the fall. A spring application can allow for increased N utilization, particularly when the soil is wet and cool.

 

Manure Application

Manure can be a good multiple nutrient source of N, P, K, and micronutrients. However, one application rate will not necessarily be optimal for all nutrients. Nutrient content of manure varies depending on the type of livestock, ration being fed, and storage and handling of the manure. You should have the manure analyzed for nutrient content before application in order to plan an efficient fertilization and management program.

To receive the most benefit from manure applied for N, you should apply manure sources that have high inorganic ammonium content, like liquid swine manure, in the fall after soils cool. Fall application can also give manure that is mixed with considerable bedding a longer time-period for microbial mineralization of inorganic N, which can increase N availability to the crop. Since N in manure is subject to volatilization, injection or immediate incorporation can reduce potential losses associated with surface application. Manure applications should be managed to reduce the chances of P loss with runoff. Injection or incorporation of fertilizer products into the soil, avoiding application to frozen or sloping soils, and managing soil residue cover can help to reduce P loss in runoff, and reduce N loss.

 

Nutrient Removal

Fall fertilizer rate recommendations should also account for nutrient uptake and nutrient removal by the crops in your rotation. Corn and soybean nutrient removal can vary based on soil conditions, yields, product differences, and fertilizer rates (Table 1). Soil tests can give an estimate of how much fertilizer is needed based on crop yield.

Table 1. Nutrient removal (lbs/bu) in harvested corn and soybean grain.*
Nutrient 
Corn  
Soybean
Nitrogen
0.67 
      3.30**   
Phosphorus (P2O5
0.35 
0.73
Potassium (K2O) 
0.25 
1.20
*Nutrient removal refers to the quantity of nutrient removal from the field at harvest. Reported nutrient removal coefficients may vary regionally depending on growing conditions. Use locally available data whenever possible.
**Most N harvested comes from the atmosphere.
Source: International Plant Nutrition Institute. 2014

 

Download PDF​​​​

By: |

Sources:

Sources:
1 Nutrient removal by selected crops. Table 4.5. 2014. International Plant Nutrition Institute. http://www.ipni.net/article/IPNI-3296.  2 Hoeft, R.G., Nafziger, E.D., Johnson, R.R., et al. 2000. Modern corn and soybean production. Chapter 6. Nutrient management for top profit. pp. 107-171. MCSP Publications, Champaign, IL.  3 Sawyer, J. and Mallarino, A. 2009. Getting ready for fall fertilization. Integrated crop management. Iowa State University. http://crops.extension.iastate.edu/cropnews/2009/09/getting-ready-fall-fertilization. 
Web sources verified 09/12/16. 130717060322