Weeds, Nitrogen, and Yield: Measuring the Effectiveness of an Organic No-Till System

2013 Annual Report for GS13-126

Project Type: Graduate Student
Funds awarded in 2013: $10,927.00
Projected End Date: 12/31/2015
Grant Recipient: Clemson University
Region: Southern
State: South Carolina
Graduate Student:
Major Professor:
Dr. Geoff Zehnder
Clemson University

Weeds, Nitrogen, and Yield: Measuring the Effectiveness of an Organic No-Till System


The experiment site was selected, prepared and seeded with a winter cover crop mix of cereal rye (Secale cereale) and crimson clover (Trifolium incarnatum) in October 2013. Prior to seeding, the experiment site was limed to increase soil pH and a composite soil sample of the field was taken. The field has since been fertilized and subplots have been marked out in accordance with the 2×3 factorial randomized complete block design.

Objectives/Performance Targets

The objectives of our experiment are: 1. To assess two tillage treatments (no-till and tilled) of a rye and crimson clover cover crop for organic tomato and summer squash production; 2. To determine the interactions between two tillage treatments and three fertilization treatments (no nitrogen fertilizer, half the recommended rate of nitrogen fertilizer, and full recommended rate of nitrogen fertilizer) as they correspond to tomato and squash yields; and 3. To evaluate the management costs of a no-till system compared to that of a tilled system.


In September 2013, part of a 2,000m2 field at the 5-acre Student Organic Farm (certified USDA Organic) located at the Clemson University Calhoun Field Research Area was selected as the site for the two-year study. All marketable vegetables grown in the research plot for this study will be sold at the Student Organic Farm summer Community Supported Agriculture (CSA) market.

A composite soil sample of the field was taken on 02 October 2013, and the field was subsequently limed and disked to prepare the seedbed for cover crop planting. The field was planted to a cover crop of cereal rye (Secale cereale, VNS) and crimson clover (Trifolium incarnatum, VNS) on 04 October at a rate of 112 kg/ha (100lbs/ac) and 39kg/ha (35lbs/ac), respectively. The cover crop was planted with a Kasco Vari-Slice overseeder (Kasco Manufacturing Co. Inc., Shelbyville, IN) with a 1.8 m (6 ft) planting width and 10 cm (4 in) disk blade spacing. Initially, we had planned to use rye and vetch cover crop treatments, but after some difficulties with incomplete vetch dieback during some informal no-till trials in summer 2013, we decided that rye and crimson clover, both of which had been grown on the farm in previous years, might produce more usable results than rye with vetch. The cover crop was fertilized in February 2014 with a fast acting, all-purpose 0-5-5 liquid fertilizer (Organic Biolink®) at a rate of 9.3 liters/ha (1 gal/ac) to correct a phosphorous deficiency that began to appear in the rye cover crop. (The analysis from the composite soil test from October showed phosphorous in the “medium” range, and we had planned to fertilize the cover crop after it over-wintered — the moderate deficiency was not surprising.) The field was then fertilized again in March with a slower release 0-10-0 phosphorous fertilizer (Hi-Yield Bone Meal®) at a rate of 448 kg/ha (400 lbs/ac) to further correct the phosphorous deficiency and prepare the field for the tomatoes and squash. 

Three blocks, each comprising four 3-row subplots, were staked out in February 2014. The subplots represent the four tillage x crop treatments: no-till squash, no-till tomatoes, tilled squash and tilled tomatoes. Each subplot will be divided into three rows prior to transplanting with each row receiving a different level of nitrogen fertilizer: no nitrogen fertilizer, half the recommended rate of nitrogen fertilizer, and full recommended rate of nitrogen fertilizer. We felt using a fertilizer treatment — specifically a nitrogen-only fertilizer — would test the cover crop’s ability to feed the vegetable crop throughout the season and would make for an interesting no-till vs. tilled comparison. Tomato seedlings, (‘Celebrity’) were started in March; summer squash (‘Success’) will be started in late April. All plants will receive starter fertilization in the greenhouse as seedlings. Transplanting will be done by hand.

Prior to cover crop termination, samples will be taken of the research plot to estimate biomass produced by the cover crop. No-till termination will be accomplished by a 2.4 m (8 ft) roller/crimper (I & J Manufacturing, Gap, PA). Tilled termination will be done by first mowing the cover crop with a 1.5 m (59 in) flail mower (Caroni SPA, Cuneo, Italy); the finely chopped residue will then be incorporated into the soil with a rototiller. The data-intensive portion of the experiment will really get underway after transplanting: soil sampling, percent cover crop dieback estimation, weed-management inputs, irrigation scheduling, and, of course, vegetable yield. 

Impacts and Contributions/Outcomes

This research is about identifying practices that will promote resource conservation and enhance small-farm vegetable production. We are hoping to demonstrate that organic no-till can be used to as a viable agricultural practice to raise marketable vegetables while reducing both on- and off-farm inputs.


Dr. Robin Kloot

[email protected]
Research Associate Professor
University of South Carolina Earth Sciences and Resources Institute
1233 Washington Street
Suite 300
Columbia, SC 29208
Dr. Dara Park

[email protected]
Assistant Professor
Clemson University College of Agriculture, Forestry and Life Sciences
E143 Poole Bldg
Clemson, SC 29634
Shawn Jadrnicek

[email protected]
Farm Manager
Clemson University Student Organic Farm
E143 Poole Bldg
Clemson, SC 29634