Potassium management and soil testing in high tunnel tomato production

Project Overview

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

Annual Reports


  • Vegetables: tomatoes


  • Crop Production: organic fertilizers, tissue analysis
  • Education and Training: extension
  • Production Systems: integrated crop and livestock systems, organic agriculture
  • Soil Management: soil analysis

    Proposal abstract:

    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. To be able 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, 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 Potassium 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.

    Project objectives from proposal:

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


    A range of levels of K (0 through 900 lbs./acre) will be applied in a randomized and replicated design in five high tunnels (three in Maine, two in New Hampshire). Other macronutrients will be provided to meet commercial vegetable production guidelines. Throughout the growing season, soil K levels, plant tissue K levels status, plant growth characteristics, yield and fruit quality will be measured.


    The proposed budget will be used to fund data collection and plant tissue testing during year two of the experiment (Summer 2015) for the tunnel located at UNH.


    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.


    Accurate soil test recommendations are based on the critical soil test level, which is the level above which there is no additional response to additional applications of specific elements. These levels are determined by measuring yield response within a particular production system. Critical levels for potassium using M3 and MM systems are known for field tomato production, but not for high tunnels. Critical levels for SME were first proposed by Witwer and Honma (1979) for in-ground tomato production, but these have not been verified, either in field or tunnel soils. We hypothesize that the critical soil test levels for K will be higher in tunnel production conditions than those that have been documented under field conditions.


    The proposed budget will be used to fund pre- and post-season soil testing using all three methods during year two of the experiment (Summer 2015) for the tunnel located at UNH.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.