SPATIAL VARIABILITY OF PHOSPHATASE, UREASE, PROTEASE, ORGANIC-CARBON AND TOTAL NITROGEN IN SOIL

The spatial variability of urease, phosphatase, casein-hydrolysing activities, organic C and total N was evaluated in a 5 yr old grass-legume association. Twenty four soil samples from the superficial layer (0-20 cm) were collected from a 15 x 40 m meadow. Samples were air-dried, sieved, and then stored at room temperature for 1 yr before being analysed. The enzymatic activities found after this time period are considered to be mainly due to enzymes protected and stabilized by their association or entrapment with clay minerals and humic molecules. Four different procedures of statistical analysis were carried out: Analysis of Variance, statistical comparison of Coefficients of Variation, Principal Components Analysis and Proximities Analysis. With each procedure, urease activity was the most variable parameter and total N the least variable parameter. Phosphatase and casein-hydrolysing activities showed a similar variability. Organic C was the least variable property when a comparison among the coefficients of variation of the means was carried out, but it was the most variable property when using the analysis of variance test. These contrasting results can be explained by the fact that organic C analytical variability is so low as to make its effective spatial variability very important. Phosphatase was correlated with protease and total N (P < 0.001) and with organic C (P < 0.005). Protease was correlated with organic C (P < 0.005) and total N (P < 0.01). Total N was correlated with organic C (P < 0.05). The sign of all these correlations was positive. Newman-Keuls multiple range test and Principal Components analysis gave complex patterns of between sample differences.