Exploiting P in heavily P-dressed fields in Sweden

摘要

Phosphorus status of soils is regarded a component of soil fertility. This component can be influenced by cropping measures. In 1983 a number of Swedish fields with a high P status were identified. In all there were 17 fields chosen distributed overSweden. On these fields P fertilizer experiments were started with the treatments 0, 15 and 30 kg P ha~(-1) yr~(-1). In average of all experimental sites the starting P-AL value was 19.6 mg 100~(-1)g soil. Typically P-AL in Swedish arable soils are lessthan 10 mg, so the 19.6 average is a high value. pH varied from 5.1 to 7.3 with 46 percent of the sites having initial pH values less than 6.2. With no P applied the P-AL values decreased significantly with time. The slope of the regression line indicates that P-AL in the top soil decreased with 0.5 units year~(-1). The decline was statistically significant at the 5 percent level. When 30 kg P year~(-1) was applied the decline was insignificant. In the high pH range (>= 6.2) the decline in P-AL was 0.67 units year~(-1) compared with 0.18 in the low pH group. Measurement of the uptake and removal of P with harvest products was chosen as the best method to analyse the crop response with time. When the experiments were pH grouped and the effects in cereals were analysed a positive effect on the P uptake with time was found.