Can foliar urea reduce nitrogen losses from potato production in Atlantic Canada?


01 Apr 2014

Project Description

Objectives: The objectives of this bridge funding are to sustain plots established in 2013 for the evaluation of the use of foliar urea to increase N use efficiency in potato production in Atlantic Canada. Specifically the funding will support a second year of this project. This information will address the following specific objectives:
    1. To evaluate whether in-season foliar urea (Right Product, Right Time, Right Place) in combination with reduced N fertilizer rates (Right Rate) at planting is an effective BMP for sustaining potato yields and reducing nitrous oxide (N20) emissions and nitrate (N03-) leaching.
    2. To evaluate the use of nitrate exposure (NE) and anion exchange membranes (IEMs) for assessing the potential for N loss

Background: The potato is the most important vegetable crop in Canada, accounting for 32% of all vegetable farm cash receipts (FCR) and 18% of all horticultural FCRs in Canada, or $972 million in the 2010 calendar year. The major producing provinces are Prince Edward Island (24%), Manitoba (20%), New Brunswick (14%), Alberta (14%}, Quebec (12%}, and Ontario (11%). Potatoes are an economically important crop in eastern Canada (defined here as Quebec and Atlantic Canada). In 2009, approximately 145,000 ha of potatoes were harvested in Canada, of which about 50% was in eastern Canada (Statistics Canada 2010). A large proportion of this potato production is grown for processing (primarily French fry) and a smaller proportion for seed as well as for the table market (Zebarth et al. 2012).

Potato is a high N demanding crop with as much as 200 kg N ha-1 being applied to Russet Burbank, the dominant potato grown in Atlantic Canada (Zebarth et al. 2003). The potential for N loss to the atmosphere as N20 or to water as N03- and N20 is significant. In Prince Edward Island the impact of potato production on groundwater N03- has become a significant issue and has been the focus of policy development and legislation (Commission on Nitrates In Groundwater 2003). There is a need to develop and demonstrate beneficial management practices (BMPs) that will sustain potato yield and quality while reducing N losses. Nitrogen losses are primarily associated with the accumulation of N03- in the soil. Technologies that improve the synchrony between the availability of N to the plant and plant N demand will reduce the unnecessary accumulation of N03- and therefore reduce the risk of N loss. In this work we will firstly develop a potato N demand function that will reflect the influence of climate on plant N demand, and use this N demand function in combination with our soil N supply function (Georgallas et al. 2012}, to examine the influence of soil properties, climate and management practices on the synchrony of these two functions. The risk of N loss can be identified through the lack of synchrony between these two functions resulting in N03- accumulation, and consequently can provide the context for evaluating various 4R strategies for optimizing N management for potatoes in Atlantic Canada.

In recent years it has become increasingly popular for potato producers in Atlantic Canada to include urea in the foliar applications of fungicides. Producers believe this practice sustains their potato crop through periods of water stress and allows for more rapid recovery following a precipitation event. This urea application is not considered as part of their N fertility program and is added in addition to the recommended rates of N fertilizer at planting. While it has long been known that foliar urea is an effective means of fertilizing the potato crop (Button and Hawkins 1958), and that the potato crop has both a high tolerance for foliar urea application and uptake of foliar applied N (Hinsvark et al. 1953), surprisingly little research on use of foliar urea has been conducted in this region. This project will examine the potential to reduce the amount N fertilizer at planting in situations where foliar urea will be applied to the crop. It is hypothesized that the direct application of urea N to the crop may result in more efficient utilization of the applied N because plant N uptake is increased (N uptake from soil is often limited during periods of low water content) and direct application of N to the plant may reduce soil N losses. Since this application is occurring during regular fungicide applications, there is no additional time or expense required.

This project will evaluate and demonstrate the opportunities for using the right product (foliar urea vs. granular ammonium nitrate) at the right time (in-season vs. 100% at planting), in the right place (foliar application vs. in soil) and at the right rate (reduced N application due to higher efficiency of foliar urea and/or use petiole testing) to insure optimal potato production in Atlantic Canada while minimizing nitrogen impacts on air and water resources.

Plot-scale Research
A plot-scale study was initiated in 2013 in anticipation of successful funding of the CFI proposal at the Crops and Livestock Research Centre in Harrington, PE. This study built upon an existing N rate study established by Nyiraneza to include an examination of the potential for foliar urea applications to allow a reduction in the amount of N applied at planting. This study will examine a reduced rate of Nat planting (120 kg N/ha) with subsequent foliar applications of urea in relation to 180 kg N/ha at planting (current recommended rate). Two strategies of foliar urea management will be examined. Both strategies will apply a total of 30 kg N/ha in several foliar applications (~six) to examine the right timing. One of the strategies will reduce N application a planting (120 kg N ha-1) such that there is less N applied to the crop in total the other will consider an N application rate (150 kg N ha-1) that will result in a similar total N application to the crop to the recommended rate of 180 kg N ha-1. In all cases soil N testing and the measurement of greenhouse gas emissions will be performed weekly throughout the growing period and biweekly during the fall until freezing.

The treatments contained in Nyiraneza's current project are:
    1. No nitrogen (control}
    2. 120 kg N/ha applied as granular fertilizer at planting, no foliar applications (2/3 recommended rate)
    3. 150 kg N/ha applied as granular fertilizer at planting, no foliar applications (5/6 recommended rate)
    4. 180 kg N/ha applied as granular fertilizer at planting, no foliar applications (recommended rate)
    5. 240 kg N/ha applied as granular fertilizer at planting, no foliar applications (1/3 greater than recommended rate)

This project will add the following treatments:
    1. 150 kg N/ha applied as granular fertilizer at planting and 30 kg N/ha applied as foliar urea in 6 applications (5 kg N/ha each}
    2. 120 kg N/ha applied as granular fertilizer at planting and 30 kg N/ha applied as foliar urea in 6 applications (5 kg N/ha each)

The rational for selecting these three additional treatments is to complement the existing study (Treatments 1-5) and to compare to current practice (Treatment 4) where all N is applied at planting, with approaches that reduced N inputs at planting and supplements N addition with 30 kg N ha-1 as foliar urea resulting in reduced overall N input to 150 kg N ha-1 (Treatment 6) or uses foliar urea to provide equivalent N application. (Treatment 7).

  • Button, E.F. and Hawkins, A. 1958. Foliar application of urea to potatoes. Am. Potato J. 35:559-572.
  • Commission on Nitrates in Groundwater. 2008. The Report of the Commission on Nitrates in Groundwater. Document Publishing Centre, Charlottetown, P.E.I.
  • Georgallas, A., J. Dessureault-Rompre, B.J. Zebarth, D.L. Burton, C.F. Drury and C.A. Grant. 2012. Modification of the biophysical water function to predict the change in soil mineral nitrogen concentration resulting from concurrent mineralization and denitrification. Can. J. Soil Sci. 92:695-710.
  • Hinsvark, O.N., Wittwer, S.H., and Tukey, H.B. 1953. The metabolism offoliar-applied urea. I. Relative rates of 14C02 production by certain vegetable plants treated with labeled urea. Plant Physiol. 28:70-76.
  • Zebarth, B.J., Leclerc, Y., Moreau, G., Gareau R., and Milburn, P.H. 2003. Soil inorganic nitrogen content in commercial potato fields in New Brunswick. Can. J. Soil Science 83:425-429.
  • Zebarth,B.J., Bellanger, G., Cambouris, A.N. and Ziada, N. 2012. Nitrogen fertilization strategies in relation to potato tuber yield, quality, and crop N recovery. Pp. 165-186. lin Sustainable Potato Production: Global Case Studies. Zhonqi H., R.P. Larkin and C. W. Honeycutt (eds.). Springer, New York.