Leopold Center played key role supporting basic soil tests

The Leopold Center has funded hundreds of competitive research grants over the last 30 years. Many of the research projects were the beginning of something that became common practice or a discovery of a new way to farm that was beneficial for the soil, water and a farmer's bottom line. The mission of the Center is to identify and develop new ways to farm profitably while conserving natural resources. This article from the Summer 2007 Leopold Letter is one example of how a research project grew into a common practice. 

Leopold Center played key role supporting basic soil tests

By Anne Larson, Special to the Leopold Center

Soil testing has become an integral part of today's agriculture. Whether done by a farmer or a crop advisor, the economic and environmental importance of soil tests has been linked with public policy that requires careful management of nitrogen (N) and phosphorus (P). 

Most recently, the Center has supported efforts to educate farmers regarding the P-Index, a tool developed by scientists from ISU, the United States Department of Agriculture (USDA) National Soil Tilth Laboratory, and the USDA Natural Resources Conservation Service (NRCS). The Leopold Center funded research by ISU agronomy professor Antonio Mallarino and the now-retired James Baker (ISU Agricultural and Biosystems Engineering) for the development of the P-Index and explored soil P thresholds.

Iowa's N-management programs have been in place since 1982, with initiation of the Big Spring Basin, Integrated Crop Management, and Model Farm demonstration projects. The Iowa Groundwater Protection Act of 1987 created the Leopold Center and as well as other initiatives to protect water resources.

Through the years, the Leopold Center has been a key player in development and implementation of improved soil tests for various nutrients, following its legislative charge to "identify and reduce the negative environmental and socio-economic impacts of agriculture" and "research and assist in developing emerging alternative practices that are consistent with a sustainable agriculture."

The N and P management tools have markedly different histories but both have the potential to reduce costs and off-site environmental effects of fertilization while maximizing crop benefits.

N test effective, use grows slowly

Groundwater testing in the early 1980s showed alarming rates of nitrate in Iowa. Nitrogen moves easily in the soil profile and is water soluble so careful and timely application of the nutrient is crucial. Acknowledging the public health consequences of such elevated concentrations, efforts were initiated to encourage reduced rates of fertilization.

An important focus of these efforts was to move farmers away from simple goal-based recommendations to a system that accounts for influences such as weather, and the form or timing of N fertilizer application, all of which figure heavily into losses and availability of N to the crop.

Among the Center's early efforts was development of the late-spring soil test for nitrogen, developed at Iowa State University by the late Alfred Blackmer and based on prior work done by the University of Vermont's Fred Magdoff. Throughout the early 1990s, the Center supported a variety of work by Blackmer and others evaluating the effectiveness of the test and exploring producer attitudes about the test. 

The N-Trak soil test kit developed by Blackmer was marketed by Hach Company to test soil nitrate when corn reached six to 12 inches tall. Research showed that this time frame was optimal for achieving corn response from N application.

Blackmer's work also confirmed that losses of N fertilizer soon after application were important, that the yield goal has little or no impact on the optimum N fertilization rate, and that carryover N was less important than generally believed. That research and other projects resulted in current ISU guidelines for N fertilization that to not consider yield goals.

Although the late-spring soil test was introduced in 1990, it was not readily adopted by Iowa farmers. A Leopold Center-sponsored study showed that less than one-half of 1 percent of farmers had purchased the text kit, and many of those didn't use the kit even though they owned it.

By 2002, Paul Lasley's Iowa Rural Life Poll showed that 12 percent of farmers were testing at a moderate to heavy rate. There are no recent surveys available on the use of the test, but it appears that some inroads have been made in changing producer attitudes about testing for the amount of N needed at a time when response will be most dramatic.

One of the barriers that kept farmers from testing soil samples in late spring was the time it took to get results back from a lab. They need a quick turnaround to permit timely sidedressing. The Hach Chemical kit allowed growers or consultants to analyze their own samples in a matter of minutes. Now most commercial labs provide the analysis in 48 hours or less, thus eliminating the need for individual test kits. Many different types of kits are also commercially available and used by crop consultants. In recent years, government programs such as EQIP and CSP have begun to provide incentives to growers who use this test.

To date, no other method of making N fertilizer recommendations has shown as high an accuracy as the late-spring nitrate test in Iowa. The development of this test has helped increase growers' profitability, but at the same time it often has reduced the total amount of N applied. The biggest benefit is that it has provided a data-based system for N management and evaluation.

A review of Leopold Center grants shows that since 1992, the Center has invested about $260,000 in projects aimed at developing, fine-tuning, and assessing adoption of the late-spring soil nitrate test.