Employing Nitrogen Budgets for Assessment of Nitrogen Loss From Agricultural Systems: A Florida Case Study On N Management in Sandy Soils.

Agriculture is a multi-billion-dollar industry in Florida ranking second nationally in value of vegetable production and 7^th in all crops with 47,500 commercial farms using a total of 3.74 million ha. Water quality issues of high nitrate–N concentrations and increasing incidents of algal blooms in springs have raised concerns in Florida over the past several years. Agriculture is considered the most prominent non-point source of nitrogen (N). Management of N is critical, especially in sandy soils which have low water and nutrient holding capacities. Thus there is a need for quantifying the sources and sinks of N for agricultural operations. Quantification of inputs and outputs for a production system will give a better insight on the probable pathways leading to N losses to the environment and to solutions to reverse N loss. The objective of this study was to quantify the inputs and outputs of N associated with potato and sweet corn cultivation on a diversified farm in northern Florida with sandy soils and center-pivot irrigation for a period of three years. Nitrogen budgets were prepared by quantifying the inputs and outputs of N associated with the production systems. The budgets indicated average total N recoveries of 67%, 45%, and 59% in potato for 2010, 2011, and 2012 respectively and 58%, 77%, and 56% in sweet corn for 2010, 2011, and 2012 respectively. The average unaccounted-for N losses to the environment were 88, 157 and 105 kg ha^-1 N for potato production and 115, 51 and 129 kg ha^-1 N for sweet corn production in years 2010, 2011, and 2012 respectively. The primary pathways associated with these unaccounted N losses were hypothesized to be leaching and volatilization.