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Nitrogen Fertilization Practices for Sequential Cropping of Wheat, Turnips, and Sweet Corn¹

ABSTRACT

The fertilizer requirement for multiple or sequential cropping needs to be better defined. Therefore, a three-crop field experiment was conducted on a Warden silt loam (coarse-silty, mixed mesic, Xerollic Camborthids) to study the effects of preplant soil mineral N and rates of applied N on yield and N uptake by spring wheat (Triticum aestivum L.), turnips (Brassica rapa L.), and sweet corn (Zea mays L.). Spring wheat and turnips were grown sequentially in 1979 followed by sweet corn in 1980. Wheat yield was not significantly increased with over 135 kg N/ha, but near maximum yield of 7.5 Mg/ha on the yield curve was at 180 kg N/ha. The concentration of N in the straw and grain continued to increase with N rates of 180 and 270 kg/ha. Yield of turnips (roots plus tops) which reached 5.8 Mg/ha and N uptake increased with increasing N rates up to the maximum use of 270 kg/ha. Only the highest rate of N applied for wheat significantly increased yield and N uptake of the following turnip crop. Sweet corn yields increased to 23 Mg/ha with increasing N rates up to 135 kg/ha, and then leveled off, whereas N uptake increased up to 180 kg N/ha. Residual effects from N applied for previous crops increased yield and N uptake of sweet corn. Responses by corn to residual N were greatest where N was applied for both wheat and turnips and least where N was applied for spring wheat only. It was concluded that turnips benefited less than sweet corn from residual and mineralizable N. The total N uptake by three crops exceeded the amount of N applied showing that N mineralization during crop growth was an important factor in the N uptake by the crops.

¹ Scientific Paper no. 6230, College of Agriculture Research Center, Washington State University, Pullman, WA 99164, Projects 0067 and 0580. Reported at the 1980 annual meeting, Am. Soc. of Agron., Detroit, Mich., 30 Nov.–5 Dec. 1980.

² Graduate Trainee and Professor of Soils, Department of Agronomy and Soils, Pullman, and Soil Scientist, Irrigated Agriculture Research and Extension Center, Prosser, respectively. Present address of senior author: Faculty of Agriculture, Chiangmai University, Chiangmai, Thailand.

Received for publication May 6, 1982. Accepted for publication August 11, 1983.