Charles Karemangingo1, Jacques Lavoie2 , Charles Everett1 and Daniel Savoie3
Partner: The New Brunswick Potato Agency
Abstract: This study was undertaken from 2000 to 2002 in order to determine the potato response to P fertilizer in soils containing very high levels of phosphorus (above 78 ppm Mehlich-3 P). Two potato varieties were used: Shepody and Russet Burbank. Each year, six P fertilizer rates varying from 0 to 165 kg P2O5 ha-1 and 33 kg of increment in 2000, and from 0 to 200 kg P2O5 ha-1 and 40 kg of increment for the two subsequent years, were band-applied in the Spring. In 2002, two demonstration fields, one field per variety, were added to the study, based on the results obtained during the first two years. Each field was sub-divided into two sections. The rate of 60 kg P2O5 ha-1 was band-applied on the first section based on the phosphorus level and saturation percentages of the soil. The second section became the control. The results indicated that in very-high-P soils, neither Russet Burbank nor Shepody responded to P fertilizer applications. Such results were consistent with those obtained from the demonstration fields. Potato yields appeared to be more site-specific than to P application rates. The marketable yields varied from 28.3 to 32.9 tonnes tubers ha-1 (the highest of the three years) in 2000 and from 21.2 to 23.0 tonnes ha-1 (the lowest of the three years) in 2002 for Shepody. However, for Russet Burbank, the yields remained more stable in 2000 and 2001 (± 19.0 tonnes ha-1) and slightly higher in 2002 (± 21.0 tonnes ha-1). Early in the season, P uptake by the two varieties increased with increasing rates of P applications as monitored through petiole P testing. Such an effect decreased with the crop growth and disappeared at the phase IV (10 to 12 weeks). In addition, residual phosphorus in soils in the fall increased with increasing P applications in the previous spring. In the fall, the maximum increases averaged over all the P applications greater than 100 kg P2O5 ha-1 were 10, 30, and 30 ppm P under Russet Burbank and 10, 19, and 22 ppm P under Shepody as compared to the control for 2000, 2001, and 2002, respectively. In conclusion, the results of this study confirmed that the decrease of P fertilizer applications on Russet Burbank and Shepody potato varieties grown in soils containing very high levels of phosphorus does not have any negative effect on the tuber yield and quality. Rather, decreasing phosphate fertilizer application minimizes soil P build-up and potential risks associated with P transport to the water bodies.
1Land Development Branch, Department of Agriculture, Fisheries and Aquaculture, P.O. Box 6000, Fredericton, NB, E3B 5H1
2Potato Development Center, Agriculture Development Branch, Department of Agriculture, Fisheries, and Aquaculture, Wicklow, NB
3Agriculture Development Branch, Department of Agriculture, Fisheries, and Aquaculture, Grand Falls, NB