Effects of Pre-Plant and In-Season Nitrogen Management Practices on Tuber Yield and Quality of Two Potato Cultivars

ABSTRACT A good balance in pre-plant and in-season nitrogen (N) application is important for optimal production of high quality potato (Solanum tuberosum L.) tubers in coarse texture soils, to improve N uptake efficiency, and minimize N losses. Field experiments were conducted in a Quincy fine sand (mixed, mesic Xeric Torripsamments) in the Columbia Basin region in the Pacific Northwest under center pivot irrigation. In the first year (2000), ‘Russet Burbank’ and ‘Umatilla Russet’ cultivars were grown with 112 kg·ha− of N as pre-plant soil application. In-season fertigation was done with 224 kg·ha− of N in either 2, 5, 10, or 20 doses starting three weeks after emergence. In-season N frequency had no significant effects on the tuber yield (60 Mg-ha−) or quality of both the cultivars. The second year (2001) ‘Ranger Russet’ and ‘Umatilla Russet’ cultivars were grown with either 56, 112, or 168 kg·ha− pre-plant N treatment (including the soil residual N content). The total N over the entire growing period was 336 kg·ha− across all pre-plant N treatments. An additional treatment of 448 kg ha− total N was also evaluated with 112 kg·ha− pre-plant N. Within these four main treatments, sub-treatments comprised application of in-season N fertigations at 2, 3, or 5 frequencies starting three weeks after emergence. The tuber yields of both cultivars were not significantly influenced by either different pre-plant N rates (56 to 168 kg·ha−) or total N rates (336 to 448 kg·ha−). This study was repeated the third year (2002), except in-season N fertigation was evaluated at either 5 or 10 frequencies. The results of these studies demonstrated that N application in excess of 336 kg·ha− rate failed to show any beneficial effects in terms of total tuber yields, or yields of different size grade tubers. Tuber specific gravity was also not significantly influenced by the different pre- plant N rates or total N rates. In-season N application through the irrigation system is a convenient method of fertilizer delivery without an added cost of application. The range of N management options, evaluated in this study for two potato cultivars, resulted in non-significant differences in total tuber yield as well as tuber quality. Nitrogen leaching loss below the rootzone was not evaluated. However, it is advisable to apply the low pre-plant soil N rate (56 kg ha−; including the soil residual N) with remainder (280 kg·ha−) as in-season fertigation for production of high yields of good quality tubers in the Pacific Northwest production conditions.