ABSTRACT


Hernán Tejeda S.1
 
The associatin between nitrogen mineralization rate and selected chemical characteristics of trumao and no-trumao soils were studied. Trumao soils are derived from recent volcanic ash. Under the name of no-trumaos were grouped soils derived from ancient volcanic ash, granitic rocks and glacial-alluvial deposits. Mineralization rate was estimated by determining the amount of N - (NO3 + NO2 + NH4) produced during incubation of soil samples at 30º C for 14 days. The association between N mineralization and total-N, C/N ratio, available P, log (extractable-al) and pH was studied using simple correlation and regression analysis. Each soil group was studied separatelly. Regression analysis was used to elucidate multicollinearity problems, say, when two or more variables associated with mineralization were correlated one with another.
Only pH was was not significatively correlated with N mineralization in the trumao soils, which are very high in total-N and extractable-Al. Besides their significant correlation at. 01 level wich N mineralization, the C/N ratio and available-P showed significant r values at. 05 level with total-N and log (extractable-Al). The last 2 variables correlate at the. 01 level of significance with mineralization. Results of the regression analysis shöwed that elimination of the C/N ratio and available-P from a model including the four variables that showed significant correlation with mineralization did not reduce significatively the regression sum of square. This result showed that the correlation between C/N ratio and available-P with mineralization was due to multicollinearity with total-N and extractable-Al, and that only the last two variables showed a direct association with mineralization. The negative affect of extractable-Al upon mineralization rate may be due to formation of stable complex between organic matter and the highly reactive aluminum from the alofan in trumao soils. Only total-N showed significant correlation coefficient at the. 01 level with N mineralization in the no-trumao soils, wich are medium to low in total-N and low in extractable-Al. It may be that, due to low levels, total-N is the main limiting factor.
Keywords:
1Ing Agr MS, Estación Experimental Quilamapu, Instituto de Investigaciones Agropecuarias, Casilla 426, Chillán, Chile.