Interpretive Summaries:

At three sites, various three- to four-year crop rotations were implemented. Wheat has been grown every year at all sites, corn every year at Sterling, and sorghum every year at Walsh. In the original experimental design, half of each plot received P fertilizer every year, and the other half received no P fertilizer. The purpose was to determine if organic P cycling would satisfy the P needs of the crops in these no-till dryland cropping systems. By 1992, the wheat emergence and growth in the no-P side of the plots were becoming very poor, thus demonstrating the importance of P fertilization in the sustainability of intensive crop production. Therefore, the decision was made to initiate P fertilization of the whole plot every time wheat was planted (i.e., every three to four years). Annual P applications were continued on plots where originally implemented.

One objective of this study is to determine if carryover of P applied to wheat is adequate to satisfy the needs of dryland corn in the rotation. Results to date indicate that there is enough P fertilizer carryover from the previous winter wheat crop to meet the needs of the dryland corn crop in the rotation. CO-11F