Building Soils for Better Crops, Third Edition

Making Adjustments to Fertilizer Application Rates


If information about cropping history, cover crops, and manure use is not provided to the soil testing laboratory, the report containing the fertilizer recommendation cannot take those factors into account. Below is an example of how you can modify the report’s recommendations:

Past crop = corn

Cover crop = crimson clover, but small to medium amount of growth

Manure = 10 tons of dairy manure that tested at 10 lbs of N, 3 lbs of P2O5, and 9 lbs of K2O per ton. (A decision to apply manure was made after the soil sample was sent, so the recommendation could not take those nutrients into account.)

Worksheet for Adjusting Fertilizer Recommendations
Soil test recommendation (lbs/acre)12040140
Accounts for contributions from the soil.Accounts for nutrients contributed from manure and previous crop only if information is included on form sent with soil sample   
(Use only if not taken into account in recommendation received from lab.)   
Previous crop (already taken into account)-0  
Manure (10 tons @ 6 lbs N, 2.4 lbs P2O5, 9 lbs K2O per ton, assuming that 60% of the nitrogen, 80% of the phosphorus,  and 100% of the potassium in the manure will be available this year)-60-24-90
Cover crop (medium-growth crimson clover)-50  
Total nutrients needed from fertilizer101650
Table 21.4: Soil Test Categories for Nitrogen Tests
A. Pre-Sidedress Nitrate Test (PSNT)*
B. Deep (4-ft) Nitrate Test (Nebraska)
CategoryVery LowLowOptimumHighExcessiveCategoryVery LowLowOptimumHighExcessive
Probability of response to added nutrientVery HighHighLowVery Low Probability of response to added nutrientVery HighHighLowVery Low 
Nitrate-N (ppm)0-1011-2223-2829-35>35Nitrate-N (ppm)0-67-1515-1819-25>25
*Soil sample taken to 1 foot when corn is 6-12 inches tall. 
Table 21.5: Amounts of Available Nutrients from Manures and Legume Cover Crops
Legume cover crops*N lbs/acre  
Hairy vetch70-140  
Crimson clover40-90  
Red and white clovers40-90  
Manures**NP2O5 lbs per ton manureK20
*Amount of available N varies with amount of growth.
**Amount of nutrients varies with diet, storage, and application method.

Note: Quantities given in this table are somewhat less than for the total amounts given in table 12.1.

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