Potassium management and soil testing in high tunnel tomato production

2014 Annual Report for GNE14-077

Project Type: Graduate Student
Funds awarded in 2014: $11,526.00
Projected End Date: 12/31/2016
Grant Recipient: University of New Hampshire
Region: Northeast
State: New Hampshire
Faculty Advisor:
Dr. Rebecca Sideman
UNH Cooperative Extension

Potassium management and soil testing in high tunnel tomato production


High tunnels are inexpensive, greenhouse-like structures used to extend the growing season and increase crop quality and yields without increasing cultivated land area. High tunnels experience reduced leaching from precipitation and higher fertilization rates, but also much higher crop yields than are seen in the field. As a result, high tunnel soils typically show high macronutrient and soluble salt levels when subjected to field soil testing methods. Over- and under-fertilization of high tunnel crops is commonly seen in New England, despite regular soil testing and fertility monitoring programs.


In order to use soil testing tools accurately in high tunnel soils, testing methods need to be calibrated under high tunnel systems. We propose to begin the process of calibrating the field soil tests commonly used in New England (Mehlich-3 and Modified Morgan) as well as the Saturated Media Extract (SME) test in high tunnel soils. For these experiments, we propose to focus on Potassium (K), an important macronutrient in tomato yield and quality.


We will identify soil test critical levels for high tunnel soils, as well as tomato yield and quality response with varying K  levels. We will also test the hypothesis that the SME test can be used to improve our ability to predict soil nutrient availability for high tunnel tomatoes. The project will provide a framework for better understanding soil fertility in high tunnel tomatoes agroecosystems.

Objectives/Performance Targets

Objective 1. Characterize the yield response relationship to potassium for high tunnel tomatoes.


A range of levels of K (0 through 900 lbs./acre) and two levels of N (300 and 500 lbs./acre) were applied in a randomized and replicated design in five high tunnels (three in Maine, two in New Hampshire). Throughout the growing season, soil K levels, plant tissue K and N levels, plant growth characteristics, yield and fruit quality were measured. After the first season of data collection and analysis, there has not been clear correlations between K levels and yield, nor has there been significant differences between treatments. However, this objective will be repeated in the 2015 growing season to better understand the relationship between K inputs and yield response.


Objective 2. Determine the critical soil test levels for potassium corresponding to maximum tomato yield and fruit quality, using Mehlich 3, Modified Morgan, and SME soil testing systems.


Throughout the growing season, multiple soil tests were taken per site to be analyzed with the Mehlich 3, Modified Morgan, and SME methods. This objective has not been assessed because the majority of the season’s soil samples are expecting analysis at the University of Maine’s Soil Analytical Lab (UMSAL) in mid January. Upon receiving soil sample analysis for all sites and sampling dates, critical K levels will be determined for each soil test and the objective will be repeated in 2015 to better understand these levels.


The first year of this two year project has been completed. In summary, tomatoes were grown in replicated designs in five high tunnels throughout New Hampshire and Maine. All experimental sites were managed independently by project collaborators, and all sites received identical treatments, soil sampling and fruit yield and quality data collection. All sites were visited multiple times throughout the season by the project manager, and additional petiole sap nutrient level data was collected and analyzed by the manager using LAQUA Twin Potassium and Nitrate meters, and by the UMSAL. Except for the data from the soil samples awaiting analysis at UMSAL in mid-January, all of the data has been collected and analyzed to meet the objectives of the first year of the two year project. At this point, conclusions cannot be made from the data and further analysis and sampling is necessary to better understand the objectives.

In January, all of the project collaborators will meet to discuss the completion of the first year of the project, discuss results, flaws, and potential improvements on experimental design. The lack of statistical significance and correlations between the treatments will be on the agenda for discussion and potential improvement.

Impacts and Contributions/Outcomes

While the first year of this two year project is nearly complete, no clear conclusions can be made yet from the data. While the majority of the data from this season has been analyzed, the overall lack of correlations and significant differences between the trials prevent a confident understanding of our objectives. Further analysis, discussion, and sampling is needed to determine whether experimental design and variability error play a role in our inconclusive results, or if there really is no clear correlation or significance between K treatments and high tunnel tomato yield.


While no conclusions can be made yet, our project is one step closer to understanding our objectives regarding high tunnel tomato management. Our first objective is to assess the interactions between amounts of K fertility and high tunnel tomato yield. This objective has the potential to affect our agricultural industry in two ways: 1. Our results may indicate that our current K recommendations for high tunnel tomatoes are too low, thus limiting the potential yields for growers, or 2. Our results may indicate that our current K recommendations for high tunnel tomatoes are too high, thus increasing production costs without increasing yields for growers.

Our second objective is to assess the soil test critical levels for K in relation to maximum high tunnel tomato yield for the common Mehlich 3, Modified Morgan, and SME soil testing methods. This objective has the potential to potentially increase our ability to evaluate and utilize high tunnel soils. Our results may indicate that the three common high tunnel soil testing methods may vary in their ability to predict accurate soil test critical K levels for maximum high tunnel tomato yield. If so, growers to better manage and likely increase yields through an increased understanding their soil nutrient profile.


Connor Eaton

Graduate Student
38 College Rd.
Durham, NH 03824
Office Phone: 2038148364
Becky Sideman

Associate Professor / Extension Specialist
38 College Rd.
Durham, NH 03824
Office Phone: 6038623203