Living Soil

Accounting for manure nitrogen value

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The application of animal manure in crop-producing agricultural fields is of great importance, especially for maize, wheat and other agronomic crops. It is the right of every modern-day farmer to know this important fact.

Animal manure adds organic carbon to the soil, which consequently improves soil health, fertility and then productivity. The microorganisms that are in the soil feed on organic carbon that is added to soil when we apply animal manure. For this reason, by adding animal manure to the soil, you are supplying food to the microorganisms that improve your soil health, fertility and quality.

Agricultural fields that are low in fertility status and poor productivity potential as a result of poor soil structure, high bulk density, and low nutrient and water holding capacity can potentially benefit from animal manure applications. While animal manure is known to improve soil quality and health (Moshia et al., 2015; Moshia et al., 2016), farmers must ensure that they do not apply manure more than two consecutive seasons in the same field.

When manure is applied to the soil, it continues to react with the soil to release nutrients and feed soil microorganisms for years. One risk of over application of animal manure or repeated application of animal manure on the same agricultural land is a threat of salt accumulation in the soil that can potentially change or break soil structure and limit microbial activities, crop growth and development.

Manure contains all essential plant nutrients, especially nitrogen, which is a chief nutrient in agricultural crop production. There have been uncertainties about how much nutrients in animal manure are available to the crops in the first year following field application where manure is applied to the soil and then mixed or incorporated into the soil. It is recommended that farmers do not exceed 44 tons/ha (17 tons/acre) of manure application per years and must not apply manure for a period exceeding two years on the same field.

Always remember to take a sample of the manure and send the sample to the accredited laboratory for analysis for Total Solids (%), Moisture (%), Organic Matter (%), Ash (%), Ph, Soluble Salts (Ec), Total Nitrogen, Organic Nitrogen, Ammonium Nitrogen, Nitrate Nitrogen, C: N Ratio, P, K, Na, Ca, Mg, Fe, Cu, Mn, Zn, B, And Al.

Let’s assume a farmer is applying 44 tons/ha of feedlot or dairy manure to the soil in 2019. When animal manure is applied to agricultural lands to meet the nitrogen requirement of the crop, 40% of nitrogen from animal manure become available to the crops in the first year of application, and from the same manure applied, 20% N becomes available to the crops in the 2nd year, and 10% N become available in the third year. That’s because animal manure is a slow nutrient release fertilizer through a process of mineralization. Feedlot manure is less moist than dairy manure, so assume a feedlot manure that has 5.94% moisture, and 1.343% nitrogen.

Manure applied = 44 tons/ha

Moisture content = 5.94%

Therefore, dry matter = 44 tons/ha (100 – 5.94%)/100

= 41.39 tons/ha

Nitrogen present in manure on dry basis = 1.343 % (from lab. Manure analysis results)

Therefore, N applied through manure = 41.39 * 1.343%/100

= 0.556 tons/ha

Only 40% of applied N through manure is available for in the 1st year of manure application.

= 0.556 *40/100

= 0.222 tons/ha *1000kg/ton

= 222 Kg N/ha (first year)

To see how many bags of urea would this be equivalent to, use the following formula:(Image)

This is equivalent to = 483 Kg urea (10 bags of urea fertilizer). ¢

M.E. Moshia, Dept. of Agronomy, The University of Fort Hare, and FAO-Intergovernmental Technical Panel on Soils, Rome, Italy, N.M. Mushia, Eastern Cape Dept.: Rural Development and Agrarian Reform, and A. Manyevere, Dept. of Agronomy, The University of Fort Hare



Moshia, M.E., Khosla, R., Davis, J.G., Westfall, D.G. and K. 2015. Precision manure management on site-specific management zones: Topsoil quality and environmental impact. Communications in Soil Science and Plant Analysis, 46(2): 235-258.

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