TEKTRAN

AN ANALYSIS OF LONG TERM NITROGEN USE IN CONTINUOUS CROPS AND ROTATIONS

Author(s):

YAMOAH CHARLES F
VARVEL GARY E
WALTMAN WILLIAM J
FRANCIS CHARLES A

Interpretive Summary:

Crop rotations can and do have advantages in farming systems. These advantages depend upon the correct crop choices in the sequence, soil fertility management, and weather factors. This study, conducted in a rainfed area of eastern Nebraska, presents information on how weather impacted cropping systems in a 12-year time span. The study illustrates how composite variables derived from simple bioclimatic simulation models can be used to predict yields. Biological windows (BW) 1 to 3 and a standardized precipitation index (SPI) were the significant composite variables. Biological windows, as defined in this paper, are indicative of soil quality and favorable temperature/moisture conditions for crop growth. BW 2 alone explained 88 percent while BW2 and May temperature in combination explained 94 percent of the variability of corn yields in corn-soybean rotation. August temperature negatively impacted corn and soybean yields, generally to a greater extent in continuous monocrops than in rotations. In addition, a preseason SPI explained up to 50 percent of the subsequent season's corn yield. Overall, yields in rotations were higher and more stable than those in monocrop systems. Nitrogen fertilization increased yields and reduced risks more in rotations than in continuous monocropping. Corn and soybean in these cropping systems appeared more sensitive than sorghum to weather fluctuations, thus making sorghum the crop choice under uncertain climates. Using these variables, future yields could be predicted by substitution of expected weather values in our model equations.

Keywords:

n fertilizer ground water greenhouse gases residue management placement water regime crop need n availability

Contact:

SOIL & WATER CONSERV. RES
119 KEIM HALL, UNL EAST C
LINCOLN
NE 68583
FAX: (402)472-0516
Email: GVARVEL@UNLINFO.UNL.EDU