Quantification of nitrogen inputs from biological nitrogen fixation to whole farm nutrient budgets of two dairy farms in Atlantic Canada.

Nimmo, J., Lynch, D.H., and Owen, J. (2013). "Quantification of nitrogen inputs from biological nitrogen fixation to whole farm nutrient budgets of two dairy farms in Atlantic Canada.", Nutrient Cycling in Agroecosystems, 96(1), pp. 93-105. doi : 10.1007/s10705-013-9579-4  Access to full text

Abstract

Legume biological N fixation (BNF) is a large source of uncertainty in farm N budgets. This study sought to quantify the BNF-N input to two whole farm nitrogen budgets and establish a simple and accurate method for incorporating BNF values as inputs in whole farm N budgets. Nitrogen inputs and outputs as well as flows of N between animal and crop production components were determined for a dairy farm in New Brunswick (NB) and Prince Edward Island (PE) over a two year period. The 15N natural abundance method was used to determine the %N derived from the atmosphere (%Ndfa) through BNF at both sites. Red clover (Trifolium pratense) at the PE site derived 77 % of its N from BNF and alfalfa (Medicago sativa) collected at both the PE and NB farms derived 72 % of its N from BNF. Total BNF-N present in legume biomass from mixed forage fields measured with the 15N natural abundance method ranged from 39 to 116 kg N ha−1 year−1. A legume dry matter conversion model adjusted with %Ndfa and %N of red clover and alfalfa samples from both farm sites was selected to estimate BNF-N inputs from mixed forage fields on the farms. Averaged across the entire cropland area at each farm site, the BNF-N inputs ranged from 27 to 52 kg N ha−1 year−1. The farmgate BNF-N inputs are low in comparison to other studies, possibly due to low legume contents in forage fields. BNF accounted for 18–29 % of farmgate N inputs at the farms. Surpluses of N found at both farm sites ranged from 98 to 135 kg N ha−1 year−1, typical to the whole farm N budgets of similar dairy farms.

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