Small-scale spatial variability of phosphorus in a paddy soil
2003
Hu, Z. | Haneklaus, S. | Liu, Q. | Xu, C. | Cao, Z. | Schnug, E.
Information about the spatial variation of phosphorus (P) in soils is required for developing site-specific P fertilizer management practices and assessing environmental effects of P fertilization. In China fields may be as small as 500 m2 and the question is whether the side by side of different farm management practices have an effect upon the spatial variation of soil P. In the present investigation, top soil samples (0-20 cm) were taken in a regular grid of 15 by 15 m in six fields with up to 12 management plots (0.06-0.4 ha). Each of these six fields was managed by 6 to 12 farmers. The elevation of the six fields varied at maximum by 1.24 m. The P content of soils was determined in the following extractants: 0.5 M NaHCO3 (Olsen method), 0.3 M CH3COOH + 0.05 M calcium acetate + calcium lactate (CAL method) and 0.43 M HNO3 (Westerhoff extract). The P content determined by the Olsen method was significant y lower than that by the CAL method and Westerhoff extract. A close relationship between Olsen P and CAL P was found (r2 = 0.60). 24% of all samples were P deficient with values < 5 mg P kg(-1) extracted by 0.5 M NaHCO3. The coefficient of variation was 34.5%, 36.9%, and 16.5% for P in the Olsen, CAL and Westerhoff extract, respectively. Topography had no significant influence on the soil P status. Geo-statistical analysis was performed in order to evaluate spatial correlations for extractable soil P. Ranges of 55 m for the Olsen method, 69 m for the CAL method and 54 m for the Westerhoff extract were determined.
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