Extending results from agricultural fields with intensively monitored data to surrounding areas for water quality management

Authors: Heilman, Philip - Phil; Malone, Robert - Rob; Ma, Liwang; Hatfield, Jerry; Ahuja, Lajpat; BOYLE, K. - Retired Non ARS Employee; KANWAR, R. - Iowa State University

Submitted to: Agricultural Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2011
Publication Date: 3/1/2012
Citation: Heilman, P., Malone, R.W., Ma, L., Hatfield, J.L., Ahuja, L.R., Boyle, K., Kanwar, R. 2012. Extending results from agricultural fields with intensively monitored data to surrounding areas for water quality management. Agricultural Systems. 106:59-71. https://doi.org/10.1016/j.agsy.2011.10.010.
DOI: https://doi.org/10.1016/j.agsy.2011.10.010

Interpretive Summary: This paper addresses the general question of how the understanding of management effects on pollution loads and farm income developed from intensively monitored agricultural study sites can be applied to a larger area. The specific question is how information about the physical and biological processes at Iowa State University’s Northeast Research Farm near Nashua, Iowa, could be applied over a large area to help farmers select management systems to reduce nitrogen loading in tile drained areas. Previous research has documented the parameterization and calibration of the RZWQM model at Nashua to simulate 35 management system effects on corn and soybean yields and N loading in tileflow from 1990 to 2003. As most management systems were studied for a 6 year period and in some cases weather had substantial impacts, a set of 30 alternative management systems were also simulated using a common 1974-2003 input climate dataset. To integrate an understanding of the economics of N management, we calculated net returns for all management systems using the DevTreks social budgeting tool. We ranked the 35 observed systems in the Facilitator decision support tool using N loading and net returns and found that rankings from simulated results were very similar to those from the observed results from both an onsite and offsite perspective. We analyzed the effects of tillage, crop rotation, cover crops, and N application method, timing, and amount for the 30 long term simulations on net returns and N loading. Our approach is an example of a proposed framework to create a quality assured database to systematically extend the intensively studied results to the larger area it represents. Currently used approaches to quantifying management effects are either not specific to tile drained agriculture, not site-specific, or focused on reducing N application without quantifying N loading.

Technical Abstract: A 45% reduction in riverine total nitrogen 'ux from the 1980–1996 time period is needed to meet water quality goals in the Mississippi Basin and Gulf of Mexico. This paper addresses the goal of reducing nitrogen in the Mississippi River through three objectives. First, the paper outlines an approach to the site-speci'c quanti'cation of management effects on nitrogen loading from tile drained agriculture using a simulation model and expert review. Second, information about the net returns to farmers is integrated with the nitrogen loading information to assess the incentives to adopt alternative management systems. Third, the results are presented in a decision support framework that compares the rankings of manage- ment systems based on observed and simulated values for net returns and nitrogen loading. The speci'c question addressed is how information about the physical and biological processes at Iowa State University’s Northeast Research Farm near Nashua, Iowa, could be applied over a large area to help farmers select management systems to reduce nitrogen loading in tile drained areas. Previous research has documented the parameterization and calibration of the RZWQM model at Nashua to simulate 35 man- agement system effects on corn and soybean yields and N loading in tile'ow from 1990 to 2003. As most management systems were studied for a 6 year period and in some cases weather had substantial impacts, a set of 30 alternative management systems were also simulated using a common 1974–2003 input climate dataset. To integrate an understanding of the economics of N management, we calculated net returns for all management systems using the DevTreks social budgeting tool. We ranked the 35 observed systems in the Facilitator decision support tool using N loading and net returns and found that rankings from simulated results were very similar to those from the observed results from both an onsite and offsite perspective. We analyzed the effects of tillage, crop rotation, cover crops, and N application method, timing, and amount for the 30 long term simulations on net returns and N loading. The primary contribution of this paper is an approach to creating a quality assured database of management effects on nitrogen loading and net returns for tile drained agriculture in the Mississippi Basin. Such a database would systematically extend data from intensively monitored agricultural 'elds to the larger area those 'elds represent.