Reducing nitrate contamination of groundwater using cover crop mixtures and tailoring nitrogen fertilizer

Reducing nitrate contamination of groundwater using cover crop mixtures and tailoring nitrogen fertilizer

Summary

Potato is an important crop in the United States and rates fourth among world crops in terms of production. There are over 2700 potato fields in Northeast United States and potato growers often over apply nitrogen fertilizer to ensure against loss of yield. High mobility of nitrate in the soil profile makes it susceptible to leach to the lower soil levels leading to ground water nitrate contamination and environmental concerns. Regardless of costs of fertilizers, nitrate contaminated water causes serious illness for infants and pregnant woman which could not be tolerated by public. Selecting appropriate type of cover crops as nitrogen scavengers along with supplementary nitrogen management can reduce nitrate leaching and water contamination. Traditionally, farmers plant rye or oat in Massachusetts which might not meet nitrogen requirements of succeeding potatoes. The objectives of this study were to 1) Evaluate influence of different cover crop mixtures on minimizing nitrate leachate caused by surplus nitrogen fertilizer application 2) Asses cover crops’ decomposition rate and its synchronization with potato nutrient demands 3) Study nutrient density and tuber yield of potatoes as affected by cover crop mixtures and nitrogen fertilizer. The student will measure nitrate leaching, cover crop decomposition rate, tuber yield and nutrient density of potatoes, and nitrogen use efficiency. The research data obtained from this project will form a basis for recommendations for potato growers in Massachusetts to alleviate nitrate leaching by proper cover crop and nitrogen fertilizer management.

Objectives/Performance Targets

1. Evaluate efficiency of cover crop mixtures in nitrate leaching reduction in a potato production system.

2. Assess decomposition rate of cover crop mixtures and determine nitrogen mineralization synchronization between cover crops decomposition and potato’s growth.

3. Evaluate yield and nutrient density of potatoes as affected by nitrogen fertilizer and cover crops.

Accomplishments/Milestones

This project contains two major phases during 2013 and 2014 growing seasons. The first phase includes land preparation and cover crops planting in fall 2013. Before planting cover crops, soil samples were collected from the experimental plots to test the nutritional background of the soil. Also, Nitrate absorbent capsules were made and buried under cover crop root zone to monitor nitrate leaching during cover crops’ growth. Each capsule contained 150 g of nitrate absorbent resin tightly packed with mesh bags to prevent mixing soil particles with resin. Cover crop seeds were weighted separately according to each species’ planting density and mixed in small bags for easier application.  Afterwards, five cover crop seed mixtures including daikon/oat, daikon/peas, daikon/rye, peas/rye, and peas/oat were planted in the field with a grain drill planter on August 25th in 2013. I addition, a no cover crop plot was considered to compare cover crop treatments with no cover crop ones. Cover crop tissue samples were taken from cover crop stands at different growth stages before frost. Also, soil samples were taken three times during the growth and before soil frost form three different soil depths (20, 40, and 60 cm). Mixed cover crop tissue samples were weighted, prepared and placed in the plastic mesh bags for the decomposition rate experiment. Two groups of samples were placed in a plot next to the main cover crop plots. A group of samples were buried under the soil while another group was fixed on the soil surface to compare decomposition rate of the samples in tilled- and no till systems. Also, soil temperature sensors were installed to monitor soil temperature changes during the experiment. Among cover crops, daikon, oat, and peas will be winter killed while rye can survive the winter and continue its growth in the spring. Tissues samples will be analyzed in distinct intervals to evaluate nutrient and weigh loss of samples when the temperature gets 45^o F in the spring. After the first phase of the experiment in fall and winter 2013, the land will be prepared for the second phase in the spring (Potato planting).  

Impacts and Contributions/Outcomes

Since only 25% of the experiment is completed, no outcomes have yet been determined. To assess the impact of cover crop mixtures in nitrate leaching prevention and also determine the synchronization between cover crop nutrient release and potato growth rate, it is necessary to analyze the cover crops, soil, and resin samples in the spring and also during potato growing season. Obviously, the results will increase our understanding of the efficiency of cover crops in nitrate leaching prevention and improving nutrient density of potatoes.

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