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Document Type

Campus-Only Access for Five (5) Years

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Plant, Soil & Insect Sciences

Year Degree Awarded

2015

Month Degree Awarded

September

First Advisor

Allen V Barker

Second Advisor

Masoud Hashemi

Third Advisor

Yeonhwa Park

Subject Categories

Agriculture

Abstract

Potato (Solanum tuberosum L.) rates fourth among the world’s agricultural products in terms of production volume and human consumption and worldwide demand for potatoes will exceed that of rice, wheat, or corn by 2020. Potato consumption has been a major part of the North American diet since early in the 17th century and as a dominant arable crop in the Northeastern United States. There are over 2700 potato fields in the Northeast United States and potato growers often over apply nitrogen (N) fertilizer to ensure against loss of yield. High mobility of nitrate form N fertilization in the soil profile makes it susceptible to leach to the lower soil levels leading to ground water nitrate contamination, other environmental concerns, and increased costs of production.

Rye (Secale cereale L.) is the most widely grown cover crop in the Northeast U.S, and its N-scavenging capacity and adaptability to the soils and climates in the region have been well documented. However, it might not be an adequate source of N for the early planted cash crops in the spring because it is not given the opportunity to grow in the spring and accumulate substantial amount of biomass. Therefore, we implemented field experiments to evaluate whether forage radish (Raphanus sativus L.) or winter peas (Pisum sativum L.) could be a more appropriate cover crop than rye in rotation with Dark Red Norland and Superior potatoes in Massachusetts. We also applied four levels of N fertilizer (0, 75, 150, and 225 kg ha-1) in combination with cover crops to tailoring N rates as an external source of N in addition to the released N from cover crop residues.

Our study centered on three major topics: (i) Cover crop decomposition rate and trend of nutrient release in a conventional or no till system to evaluate whether there is a synchrony with potato nutrient demands (ii) Tuber yield and nutrient density of potatoes as influenced by cover crops and N fertilization and (iii) Nitrogen use efficiency (NUE) indices, tuber quality, and pest control in potatoes.

Our results indicated that a conventional tilling system accelerated the decomposition process and also increased the rate of nutrient loss in the soil compared with a no till system. Among the cover crops used in this study, forage radish or peas accumulated more N than rye. Also, forage radish or peas with narrower C:N ratio released their N content in a faster trend. Potato tuber yield in both varieties was improved, and peas or forage radish outperformed than rye or no cover crop plots in this regard. Also, forage radish was advantageous over winter peas or rye in terms of providing nutrients other than N as suggested by more nutrient dense potatoes.

Cover crops, especially peas or forage radish were efficient in reducing N fertilization requirements in both potato varieties as indicated by higher NUE parameters. Potatoes planted after cover crops were less efficient in utilization of the supplied N than potatoes following fallow. Application of high rates of N fertilizer decreased NUE parameters through enhanced vegetative growth or probably environmental losses. Forage radish or peas exhibited more synchrony with potato N demands at its critical growth stages in terms of N release from residues. Cover crops did not produce potato tubers of higher quality than no cover crop plots. Colorado potato beetle infestation was lower in potato plants after rye early in the spring than with the other cover crops; however, later in the season all of the treatments showed the same infestation. Weed infestation tended to be lower in cover crop plots than in no cover crop plots, yet, rye and forage radish were advantageous over winter peas for suppressing weeds.

Overall, it is proposed that planting forage radish as early as possible in late August or early September could produce more potato yield and improve nutrient density than winter peas or winter rye. Also, to get the most out of the released nutrients, especially nitrogen, it is important to prepare the land and plant potatoes as early as possible in the spring.

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