Mass Nutrient Balances

Nutrient management regulations in the United Sates have, through implementation of NRCS 590 standard for nutrient management, focused on keeping clean water clean, reducing over-application of fertilizer and manure, and preventing direct manure losses to streams and lakes. However, ongoing work on several NY farms indicates that 60-80% of the N imported through feed, fertilizer, biological N fixation, etc. does not leave the farm through the sale of products (meat, milk, animals, crops, etc.). While current nutrient management efforts are essential for limiting losses from farmsteads and fields, reducing the load of N entering the farm gate and/or increasing the export of N will be critical for longer-term agricultural environmental management.

A mass nutrient balances is a simple estimate of nutrient loading on a farm. Using farm records, producers and farm consultants account for the nutrients (N, P, and K) imported through legume N fixation and purchased feeds, fertilizers, animals, etc. and exported through managed pathways, such as the sale of milk, meat, crops, and manure. The difference between the nutrients imported and exported on an annual basis represents the farm’s mass nutrient balance. The mass nutrient balance is not directly connected to nutrient losses to water or air, but it provides a simple measurement for assessing current and future changes on the farm relative to whole farm nutrient loading.

The table, below, displays mass nitrogen balances for range of dairy farm sizes based on a study of four New York dairies by Klausner (1997).

	Number of dairy cows per farm
	45	320	500	1300
	-- tons of N/year --
Input
Purchased Fertilizer	1.0	13.5	26.1	9.8
Purchased Feed	3.8	43.8	78.5	205.0
N Fixation by Legumes	1.3	14.6	13.9	21.3
Purchased Animals	0.0	0.1	0.0	0.0
	6.1	72.0	118.5	236.1
Output
Milk	2.0	18.6	26.4	72.8
Animals Sold	0.1	1.9	1.9	3.2
Crops Sold	0.1	0.0	0.0	0.0
	2.2	20.5	28.3	76.0
Remainder	3.9	51.5	90.2	160.1
% Remaining on the Farm	64%	71%	76%	68%

Regardless of farm size, the mass nutrient balance approach is a simple way for farmers and agricultural consultants to take stock of annual nutrient imports and exports, and subsequently identify the main causes of nutrient imbalances. Development and evaluation of alternatives to reduce imbalances could lead to improved profitability and reduced nutrient losses to water and air.