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Fig. 2. Bicarbonate-extractable P in the surface soil (0–7.6 cm) increases with rate of fluid and granular P fertilizer applied. The P fertilizers used were fluid ammonium polyphosphate (APP, 10–34–0) applied in the flood irrigation water and granular monoammonium phosphate (MAP, 11–52–0) topdressed and incorporated with flood irrigation. Soil P was higher with granular MAP than fluid APP. The soil was sampled about 1 mo after the previous fertilizer application, except in the Year 2000, where the soil was sampled at the end of the experiment about 13 mo after the previous fertilizer application. Therefore, little or no increase in soil P was measured in 2000 in contrast to the previous years. The symbols ns, +, *, ** indicate that the coefficient of determination (r2) of the fitted equation (y = b0 + b1x) is not significant at P = 0.10, or is significant at P = 0.10, 0.05, or 0.01, respectively.
