Fig. 5. Concentrations of organic P plotted against those of organic C of the soil samples taken from various depths of the control, pig slurry, poultry manure, and poultry manure mixed with litter treatments. The data points represented by the filled symbols (i.e., the samples from the 0- to 5- and 5- to 10-cm soil layers of the poultry manure and poultry manure mixed with litter treatments) were not included in the linear regression analysis. Organic C was calculated as 0.5 x organic matter (Table 1).