Estimation of Soil N Availability for Tomato Production in High Tunnel vs. Open Field under Organic and Conventional Management
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 especially true for sustainable farmers using organic sources of nitrogen such as cover crops or compost. 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. We also plan to explore the relationship between N mineralization from incubation as potentially mineralized nitrogen (PMN) and the ISNT. The results will be compared with the tomato yields under different fertility levels in a replicated field experiment that was conducted from 2007-2010. This approach has a major advantage over the other testing techniques and has value for improving N-fertilizer efficiency. We will develop fertility recommendations based on the results. If adopted, this would 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.
For the intermediate term, one of the greatest challenges organic and other growers using organic amendments face, especially during the beginning of organic management, is providing adequate fertility to meet crop need. Having more knowledge about N availability during the growing season will help growers estimate the amount ofN supplement required in the season. This would help to minimize the use of off-farm inputs and increase profitability by reducing the cost of additional fertilizer supplements, which in turn will reduce the amount of nitrate in ground water, reduce the phosphorous loading to fresh water systems and decrease the cost of production. In the short term, this project will provide us with new information on N availability for tomato production in high tunnel vs. open field under organic vs. conventional systems based on the ISNT test compared to PMN incubation. The project results will be published in extension bulletins and in peer reviewed journals.
Up to this point in my project, all the soil tests and PMN have been done. We faced some difficulties running the incubation tests which resulted in repeating these tests for the second time. Final results should be ready by the end of this year.
Impacts and Contributions/Outcomes
The evaluation plan will focus on three levels. At the initial stages of the project progress monitored will include making sure the samples are analyzed during the time period allocated. Quality control/ evaluation indicators will involve looking at the coefficient of variation for each data set in comparison to similar data from other crops/soils.
In the second stage of the project, data analysis and writing will take place in the fall of
2013 and spring of2014. Evaluation indicators will include feedback from graduate committee members and peer reviewed journal editors.
In the third stage of the project, feedback from end users (farmers and extension educators) will be obtained. Draft extension bulletins will be circulated for feedback prior to publication. The project results will also be presented at the Great Plains Veg. Growers conference (Jan. 2015). Feedback forms will be given to attendees to obtain comments on the presentation and the publication. This conference is attended by over 300 fruit and vegetable growers from Iowa, Missouri, Nebraska, Kansas, and beyond, and has been held annually for nearly 20 years.
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