Estimation of Soil N Availability for Tomato Production in High Tunnel vs. Open Field under Organic and Conventional Management

View the project final report

• 2014 annual report

Commodities

• Vegetables: tomatoes

Practices

• Crop Production: organic fertilizers
• Education and Training: extension, workshop
• Production Systems: organic agriculture
• Soil Management: nutrient mineralization, organic matter, soil analysis, soil quality/health
• Sustainable Communities: sustainability measures

There are many challenges to predict the soil available nitrogen (N) for vegetable growers in a timely manner. Soil testing and yield are used routinely to guide agricultural applications of N. Under or over fertilization is apt to occur in any given growing season.
Insufficient application of N can have serious economic consequences for the growers, whereas excessive fertilization increases the risk of environmental pollution. This is true for both conventional and sustainable farmers using organic sources of nitrogen such as cover crops or compost. The organic sources mineralize at different rates under various temperature and moisture conditions, so it is are harder to predict how much N is available and when.
The objective of this study is to estimate the soil N availability for tomato production in high tunnel vs. field under organic and conventional system using the Illinois Soil Nitrogen Test (ISNT). The ISNT estimates the potentially mineralizable fraction of soil organic N, specifically it measures the amino sugar N. Another objective is to determine if there is any relationship between N mineralization from incubation as potentially mineralized nitrogen (PMN) and the ISNT.
This approach has a potential advantage over the other testing techniques and has value for improving N-fertilizer use efficiency. We will develop fertility recommendations based on the results. If adopted, this could increase the profitability of tomato production and reduce the adverse environmental effects of excessive N and phosphorus P fertilization, especially for sustainable specialty crop producers using organic soil fertility amendments.

Introduction:

Limited soil N availability is a common problem in organic vegetable production that often necessitates in-season fertilization. Growing legume cover crops is generally the most economical way to provide plant available N in organic systems through crop rotation. However, the actual N contribution can vary widely depending on field specific conditions. Another practice in organic culture is application of composted manure. However the slow rate of N mineralization from composts makes it difficult to predict the effective N contribution. Pre- season mineral nitrogen (nitrate and ammonia) tests do not measure the amount of nitrogen that will be available later in the season.
Estimation of plant available N is complicated enormously by the dynamic nature of soil N owing largely to the effects of temperature and moisture supply on the N cycle processes. Soil tests for N that would estimate the labile organic fraction that supplies the plant through mineralization would be of great value to specialty crop growers. One test that shows much promise for organic farmers is the ISNT which analyzes the soil for amino sugar N, a fraction of soil that is easily mineralizble and that may become available for the crop during the growing season (Khan et al., 2001). This test has been shown to predict N responsive sites where liquid or composted dairy manure is applied to corn agroecosystems (Klapwyk et al., 2006). Because of its ability to predict readily mineralizable N, it may have great utility for organic fields which have received compost or manure for several years to decades, such as our research center in Olathe, KS which has been managed under these conditions for the last 10 years. The ISNT is offered commercially in some states, but the interpretation provided for the test is limited to corn growers in the region.
A second test that has been used historically is potentially mineralizeable N (PMN). In this test, soil is incubated at a controlled temperature and moisture level for a period of time, and repeatedly sampled for the mineral N fraction that is released during the incubation. Unfortunately, this test is time consuming and is not commercially available to growers. However, we will use in our trials to compare the ISNT to the PMN test on the same soil samples. Results will be compared to previously published literature on PMN and compost applications to specialty crops.

The objective of this study is 1. to estimate the soil N availability for tomato production in high tunnel vs. field under organic and conventional system using the Illinois Soil Nitrogen Test (ISNT) 2. to explore the relationship between N mineralization from incubation as potentially mineralized nitrogen (PMN) and the ISNT 3. to determine the impact of long term fertility management practices of organic and conventional on soil amino sugar-N 4. to explore the relationship between ISNT and organic matter, total carbon and total nitrogen.