Nutrient Management Research Database

Potato  (Solanum tuberosum L.)  requires  steady,  but  not  excessive  nitrogen  (N)  supply for  maximum  tuber  yield,  size,  and  solids,  as well  as  minimal  internal  and  external defects.  Although  more  costly  and  labor  intensive  than  dry  broadcast  applications,growers typically apply a majority of N via fertigation. A controlled release N fertilizer,polymer coated urea (PCU), is a possible alternative to this growers’ standard practice.A  newly  formulated  PCU  may meet  plant  demand  in  a  timely  and  efficient  manner through  temperature-controlled  release  of N  into  the  soil  solution,  thereby  possibly increasing yield and tuber quality, reducing N loss via leaching and denitrification, and reducing application costs. The objectives of this study were to determine the effects of PCU  on  the  yield  and  quality  of  Russet  Burbank  potatoes  grown in  Southeast  Idaho during  2006-2007.  Nitrogen  was  applied  at four  rates  (33,  67,  100,  or  133%  of recommended)  at  three  locations  with  four  methods  of  application,  namely:  1)  urea  at emergence, 2) urea split applied, 3) PCU at emergence, and 4) PCU pre-plant (only the67% rate) and compared to an untreated control. Results showed significant increases in US  No.  1,  marketable,  and  total  yield,  as  well  as  increases  in  crop  value  for  PCU treatments  over  the  other  treatments.  Post  harvest  soil  analyses  showed  that  nitratelevels  in  and  below  the  rooting  zone  were reduced  for  PCU  as  compared  to  uncoated urea. The optimum rate of 67% PCU applied at emergence consistently yielded higher than  the  other  treatments  and  was  significantly  greater  (4.2  Mg  ha-1or  1.9  ton  ac-1)  in marketable tubers than the grower’s standard practice. The optimum PCU rate resulted in 6 mg kg-1(ppm) less residual soil nitrate than the grower standard practice.

This study investigated the effectiveness of a commercial controlled release urea fertilizer (Environmentally Smart Nitrogen) in increasing N use efficiency, tuber yield, tuber quality, and N losses via nitrate leaching and nitrous oxide.

The fertilizer was applied at 0, 33, 67, 100, or 133% of the Idaho state recommendations (the recommended rate varied between 2200 and 280 lbs N/acre).

Fertilizer was applied in one of four ways:

1. Regular urea at emergence
2. Regular urea split applied
3. Controlled release urea at emergence
4. Controlled release urea at pre-plant (only at 67% rate)

Harvested potatoes were graded for size, shape, solids, and defects after 4-6 weeks of storage.

Total, U.S. No. 1, and marketable yields were consistently higher at the 67% rate applied at emergence and higher than the grower's standard practice (100% rate split application).

These findings suggest that the optimum N application rate with this polymer coated urea product is around 40 lbs N/ac lower than conventional fertilizer. In this trial, this resulted in a 6 ppm decrease in post-season residual nitrate. This reduction lowers the risks of nitrate leaching and nitrous oxide emissions.

Applying this polymer coated urea product at emergence appears to be the best timing of application.

Care should be taken in applying these findings in California's warmer climate.