On-Farm Strip Trials As Decision Support for P Management.

On-farm trials give farmers feedback on whether and where they are getting profitable yield responses to P fertilizer.  Field-scale strip trials (18 corn, 1 soybean) have been carried out in Missouri over the past five years to measure yield response to P fertilizer across farmer fields.  Average yield response to P over all 19 experiments was 0.03 Mg/ha, and economic response was -$134/ha.  However, in the 8 fields where the P response strips crossed multiple soil map units, profitable response to P was observed in at least one map unit in 5 fields.  Strip trials can be used to target P applications.  They can also be used to monitor possible yield penalty in fields that are not receiving whole-field P applications.