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Alfalfa Yield and Soil Phosphorus Increased with Topdressed Granular Compared with Fluid Phosphorus Fertilizer

^a Plant Sciences Dep., Univ. of Arizona, Tucson, AZ 85721
^b Dep. of Soil, Water, and Environmental Sciences, Univ. of Arizona, Tucson, AZ 85721
^c Pioneer Hi-Bred International, Inc., P.O. Box 1150, Johnston, IA 50131

View larger version (30K): [in a new window]   Fig. 1. Annual alfalfa hay yield increases in a curvilinear fashion to rate of fluid and granular P fertilizer applied in December of the previous year. 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. Yields were higher with the granular MAP than fluid APP fertilizer in 1997, but were similar in 1998 and 1999 for both fertilizers. The symbols ns, +, *, ** indicate that the coefficient of determination (r2) of the fitted equation (y = b0 + b1/x) is not significant at P = 0.10, or is significant at P = 0.10, 0.05, or 0.01, respectively.

View larger version (30K): [in a new window]   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.

View larger version (23K): [in a new window]   Fig. 3. Most of the bicarbonate-extractable P remains in the surface soil with fluid or granular fertilizer P application. The P fertilizers used were fluid ammonium polyphosphate (APP, 10–34–0) and granular monammonium phosphate (MAP, 11–52–0). The APP was applied in the irrigation water (water-run) or sprayed on the soil surface (sprayed) and MAP was topdressed. The data presented includes the unfertilized control and P fertilizer applied at 5 g P m–2. Where differences in soil P were detected, higher values were generally measured with granular MAP than fluid APP. Movement of P in the soil profile was limited and not affected by P fertilizer source, except in 1997 where an accumulation of soil P was measured between 15 and 23 cm for granular MAP perhaps due to the greater amount of irrigation water applied at the time of fertilizer application that year. Soil P was usually not affected by whether APP was water-run or sprayed. The error bars represent the least significant difference at P = 0.05 [LSD(0.05)], or if the LSD is not significant, an "ns" appears next to the data points rather than an error bar.