Phosphorus Budget and Soil Extractable Dynamics in Field Crop Rotations in Mollisols
2011
Ciampitti, Ignacio A. | García, Fernando O. | Picone, Liliana I. | Rubio, Gerardo
A better understanding of the P cycle is necessary to provide insights into management strategies that could enhance P bioavailability for crops. Our objectives were to evaluate the effects of continuous P fertilization on (i) the P budget, (ii) soil-extractable P (Pe) dynamics, and (iii) the relationship between these variables. Two crop rotations during a 6-yr period were analyzed in seven on-farm experiments: corn (Zea mays L.)–double cropped wheat (Triticum aestivum)/soybean [Glycine max (L.) Merr.] (C-W/S), and corn–soybean–double cropped wheat/soybean (C-S-W/S). Calculations of net P input considered only P removal (output) and fertilization (input). Initial soil-test P was 13.4 mg P kg⁻¹ (average for the four sites) for the C-W/S rotation and 37.9 mg P kg⁻¹ for the C-S-W/S rotation (average for the three sites). Treatment combinations were two annual rates: unfertilized and grain P removal estimation +10% (average 34 kg P ha⁻¹ yr⁻¹). Not applying P to soils testing 45 to 68 mg kg⁻¹ of initial Pe resulted in a steep Pe decline (slope 0.2 mg kg⁻¹ per unit of negative P budget). Nevertheless, soils with <25 mg kg⁻¹ of initial Pe levels resulted in a very small and gradual decline (slope 0.02 mg kg⁻¹). Use of current P rates applied by local farmers probably results in a small soil-test P buildup with time. The P required to increase Pe by 1 mg P kg⁻¹ was 11 and 8 kg P ha⁻¹ yr⁻¹ for the C-W/S and C-S-W/S rotations, respectively.
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