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Interpretive Summaries:
1997 - Critical soil phosphorus levels for alfalfa production in Northeastern California
1996 - Critical Soil Phosphorus Levels for Alfalfa Production in Northeastern California
Critical soil phosphorus levels for alfalfa production in Northeastern California, 1997
Phosphorus is the second most limiting nutrient for alfalfa production in Northeastern California following only sulfur (S). This research is re-evaluating the presently established critical levels for interpretation of the bicarbonate P soil test for alfalfa grown in this region and the method of soil sampling to accurately evaluate P variability within fields. In the spring of 1997, soil samples were taken on a 60 x 60 ft grid over a 25 A field. The field averaged 18.5 ppm, but ranged from 6 to 38 ppm in an apparent random fashion. Twenty harvest locations were selected within the field to test yield response to 300 lb P2O5/A. Preliminary spatial analysis of soil sample data indicated that 15-20 individual samples are needed to reduce variation in soil test results to a level where the soil bicarbanate P is useful in predicting the need for fertilizer P. There was no initial yield response, although tissue P levels were improved by P fertilization. CA-17F
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