Using nitrogen and phosphorus budgets as effective tools for assessing nitrogen and phosphorus losses from agricultural systems

摘要

Deterioration of water quality in the Suwannee River and springs in northern Florida has raised concerns over non-point sources of nitrogen and phosphorus from agricultural land uses. The Middle Suwanee River Basin (MSRB) is of special concern because of Karst topography, unconfined aquifers, and sandy soils which increase the vulnerability of the groundwater to contamination from agricultural operations. A four year field study was conducted on a commercial farm typical to those in the MSRB, with the objective of quantifying the major sources and sinks of N and P for three major crops grown in the basin --potato, sweet corn, and silage corn. Crop-soil systems N and P budgets were constructed and the components of the budgets were evaluated. Fertilizer N and P were identified as the primary inputs in the budgets. Average crop N removal represented 56, 61, and 65% of the mean total input N, whereas average environmental N loading rates represented 35, 34, and 33% of the mean total input N for potato, sweet corn, and silage corn, respectively. Seasonal P balances indicated positive balance (P accumulation) for potato, and positive and negative balances (P depletion or P mining from soil) for sweet corn and silage corn depending on the amount of total P received. Soil P loss risk Deterioration of water quality in the Suwannee River and springs in northern Florida has raised concerns over non-point sources of nitrogen and phosphorus from agricultural land uses. The Middle Suwanee River Basin (MSRB) is of special concern because of Karst topography, unconfined aquifers, and sandy soils which increase the vulnerability of the groundwater to contamination from agricultural operations. A four year field study was conducted on a commercial farm typical to those in the MSRB, with the objective of quantifying the major sources and sinks of N and P for three major crops grown in the basin --potato, sweet corn, and silage corn. Crop-soil systems N and P budgets were constructed and the components of the budgets were evaluated. Fertilizer N and P were identified as the primary inputs in the budgets. Average crop N removal represented 56, 61, and 65% of the mean total input N, whereas average environmental N loading rates represented 35, 34, and 33% of the mean total input N for potato, sweet corn, and silage corn, respectively. Seasonal P balances indicated positive balance (P accumulation) for potato, and positive and negative balances (P depletion or P mining from soil) for sweet corn and silage corn depending on the amount of total P received. Soil P loss risk.;Nitrogen and P exported away from the field (or farm) in plant part, represented 72, 84, and 89% of total N uptake and 89, 90 and 93% of total P uptake for potato, sweet corn and silage corn, respectively. Nitrogen left in the field in crop residues was greatest for potato and posed potential for N losses due to the fast decomposition of potato residues after vine desiccation. Use of a potato model indicated excess water above the crop ET, higher fertilizer applications than the university recommended rates and poor synchrony between plant N uptake and fertilizer application timing were responsible for leaching loss of N.