Residual Effects of N Fertilization on Dryland Spring Wheat in the Northern Plains. I. Wheat Yield and Water Use1

Abstract

AbstractData are frequently lacking to quantify the residual effects of fertilizer applications on soil nutrient availability, especially in regions of limited rainfall. Therefore, the effects of fertilizer N on yields of continuous dryland spring wheat (Triticum aestivum L.) grown on Typic haploboroll soil were determined in a field study at Mandan, North Dakota. Rates up to 540 kg N/ha applied either (i) all in 1 year, (ii) one‐third of the total rate in each of 3 years, or (iii) one‐sixth of the total rate each year for 6 years of the experiment. Average dry matter (1967–1972) at different stages of growth and average grain yields were increased significantly by increased N rate, but only dry matter at tillering was significantly affected by rate × timing interaction. With 270 and 540 kg N/ha applied in only the first year, residual effects significantly increased grain production in 4 of the following 5 years. At total rates of 135 kg N/ha or above, total grain yield for the 6‐year period was greatest for the 6‐year fertilization treatment and least for the 1‐year treatment. Average annual grain yields for the 540 kg N/ha rates were 1,700, 1,660 and 1,880 kg/ha for the 1, 3, and 6‐year treatments, respectively, and 1,050 kg/ha for the zero‐N treatment. Weight of grain produced per kilogram of fertilizer N applied usually decreased as N rate increased. At the 135 kg N/ha rate or higher, grain production per unit of fertilizer applied was greatest for the 6‐year treatments (annual fertilization). Root weight and development in the 6th year were related to the availability of soil N as reflected by fertilizer treatment.Total water use was significantly influenced by N rate or frequency of fertilization in only 2 of the 6 years. Water use efficiency (WUE) increased as N rate increased, irrespective of fertilization frequency. Highest WUE was obtained by 6‐year fertilization treatment and for most treatments WUE decreased .when annual fertilization ceased. Although residual N derived from previous fertilization seems to be very important for subsequent crop production, availability of N from residual sources was not sufficient to maintain maximum crop production over a number of years.