Agronomy and Horticulture Department


Date of this Version



Published in J. Prod. Agric., Vol. 11, no. 2,1998.


Crop rotations are designed to increase productivity and reduce costs. These advantages are contingent upon favorable weather and require appropriate management. Unpredictable weather poses risks to dryland crop production. Information on how weather affects yields in different cropping systems and how farmers could respond with management would help minimize risk and stabilize yield and income. We evaluated the effects of preseason and growing season weather variability on continuous and sequential cropping of corn, sorghum, and soybean in a 12-yr span, and suggest how management decisions could influence cropping system performance.
Models of different levels of sophistication have been developed to link yields of individual crops with weather factors. But there is a paucity of information on how weather and management affect yields in whole cropping systems. Furthermore, many models demand a large amount of input data, which is a major limitation to routine application by potential users. This study developed simple empirical models to relate yield and management with a combined index of composite weather variables in whole cropping systems.
The study was conducted from 1984 to 1995 at the Agricultural Research and Development Center near Mead, NE. Correlation and regression analyses were used to relate system performance to weather. Yield was the dependent variable and several combined indices of weather factors were predictor variables. The combined indices of weather or composite weather variables were biological windows (BW) and standardized precipitation index (SPI). Biological windows represent the time during the entire year during which rainfall and air temperature favor biological activities. The biological windows are derived from the mean monthly precipitation and temperature data. The SPI is the difference of precipitation from the long-term average (>30 yr) divided by the standard deviation, a measure used to determine how wet or dry a period of time is compared with average weather patterns, up to a certain date. Both BW and SPI are calculated with simple computer programs. Standard deviation was used as a measure of yield/income variability. Weather effects on yield and income fluctuations of the cropping systems are discussed, along with potentials for the farmer to influence this variability through management.