Impacts of Reduced Nitrogen Application During Late Growing Season on Potato Tuber Quality and Profitability

View the project final report

Commodities

• Agronomic: potatoes

Practices

• Crop Production: application rate management, fertigation
• Education and Training: extension
• Energy: energy conservation/efficiency
• Farm Business Management: budgets/cost and returns
• Production Systems: general crop production

Late season applications of nitrogen are made by many Colorado farms that produce fresh market russet potatoes. This graduate student research project was intended to determine if the applications provide a benefit to growers or if returns are higher under a more sustainable fertilizer program in which no late nitrogen is applied. Substantial negative effects on tuber quality were not observed from the applications. However, economic analysis based on yield indicated that Canela and Norkotah CO8 could produce lower returns due to excessive late nitrogen, while Rio Grande had slightly higher returns one year with late nitrogen and no difference the second year.

Introduction

Economic returns from fresh market potato crops are affected not only by conditions and diseases during the growing season but also by factors occurring during harvest and storage. Potato growers and shippers who sell to the fresh market often have significant economic losses from harvest damage as well as from pressure bruising and moisture loss (shrinkage) in storage. Immature potato tubers are more prone to shrinkage of potatoes in storage and more susceptible to bruising (Thornton, 1998). A primary cause of immaturity of potatoes at harvest is excessive nitrogen fertilization during the late growing season. Increased nitrogen applied during the later part of the growing season can increase potato yields for some cultivars but may delay harvesting, risking frost damage in areas with a short growing season. Tuber damage may increase during harvest because of tuber immaturity caused by over fertilization. Potato farmers in southern Colorado also use late growing season applications of nitrogen to reduce early blight (Alternaria solani) damage which will destroy the vines of susceptible potato varieties prior to development of sufficient yield. However, with increases in the cost of nitrogen fertilizers and a growing awareness of sustainable growing methods, many western U.S. potato growers are interested in reducing the nitrogen they apply. Research into reducing agricultural inputs such as nitrogen fertilizer is important to improving the sustainability of agricultural systems (Spiertz 2009).

While nitrogen fertilization research has been conducted many times for potatoes, results indicate that the optimum timing and rates are variable depending on cultivar (Love et al.,2005 ). Tuber moisture loss during storage has been observed as a consequence of excessive late season nitrogen and from harvesting of immature tubers or tubers with poor skin set (Thornton 1998 and Olsen 2003). Tuber moisture loss causes further economic losses due to increased susceptibility to pressure bruising of potatoes stored for the fresh market (Jayanty, 2009). This two-year Western SARE funded graduate research project focused on understanding the effects of different rates of late season nitrogen on yield, harvest damage and stored potato quality of russet potato cultivars (Russet Norkotah CO8, Canela Russet, Rio Grande Russet with Centennial Russet in 2010 and Mesa Russet in 2011). These cultivars are among the most commonly grown russet cultivars in southern Colorado and the western United States, accounting for more than 70% of acreage (40,000 acres) in Colorado (NASS 2009). Previous research examining the relationship between tuber maturity and nitrogen fertilization has focused on issues that are of great importance to potatoes grown for processing, such as tuber specific gravity. The central focus of this study was to determine whether fresh market potato growers had higher returns when additional late season nitrogen was applied or when growers avoided a late season application.

1. May-August 2010: Conduct literature review and research planning. Plant field trials of four different cultivars at SLVRC and apply treatment rates of nitrogen. Prepare spreadsheets and organize for experimental harvest.

2. September-November 2010: Evaluate tuber maturity, yield and harvest damage and prepare samples for storage experiments to determine shrink and pressure bruising. Conduct initial analysis of yield data, harvest damage data, and moisture loss data and cost and benefit analysis.

3. February-April 2011: Evaluate shrink and pressure bruise from storage experiments. Analyze results and present at grower meetings. Evaluate methodology and results to determine potential improvements for second year research. Prepare seed and land for second year field trials.

4. May-August 2011: Plant second year field trials for four varieties at SLVRC and apply treatment rates of nitrogen. Prepare spreadsheets and organize for experiment harvest.

5. September-November 2011: Evaluate yield and harvest damage and establish second year storage experiments for determining shrink and pressure bruising. Conduct initial analysis of yield data, harvest damage data and moisture loss data.

6. February-May 2012: Evaluate shrink and pressure bruise from storage experiments. Analyze results and present to grower meetings. Compare results across both years experiment data. Prepare submissions for peer reviewed journals and commercial publications. Send surveys to growers on changes made to fertilizer regime and adoptions of research results.