Atividade de amilases e de sacaridases e relaçôes com parametros climáticos e com a disponibilidade de nitrogênio para laranja-doce

A trial was carried out in a Dark-Red Latosol cultivated with Citrus sinensis L. Osbeck (Valencia sweet orange cultivar) in Jaboticabal county, State of Sao Paulo, Brazil, with the objective of correlating soil amylase and saccharidase activities with soil ammonium-N, soil nitrate-N, soil moisture, climatic parameters (air temperature and rainfall), leaf mass and leaf N content. The experimental design was completely randomized, consisting of twenty-five sampling dates with six replications. Soil and leaf samples were collected every 14 days, from March to January. Soil samples were taken on the shoot line projection at the depth of 0-20 cm, while leaves number +2 and +3 were collected from branches containing fruits of the year. Saccharidase activity was significantly correlated with the soil moisture at the moment of soil sampling (r = 0.46 * ); with the mean air temperature during the day before soil sampling ( r = 0.44 * ); with the mean of the maximum (r = 0.43 * ) and of the mean (r = 0.40 * ) air temperatures during the two days before soil sampling; and with the mean of the maximum air temperature (r = 0.43 * ) and total rainfall (r = 0.51 * ) during the five days prior to the sampling date. Amylase activity was not correlated with these climatic parameters. Amylases and saccharidases were present in the soil over the experimental period, but from March to July there was not enough substrate for maximum enzyme activity. From August to early January the content of nonreducing carbohydrates increased in the soil and starch content was enough to saturate the active sites of amylases. The correlation between amylase and saccharidase activities was low and depended upon sampling time: it was inversely and not closely correlated in the period from March to July (r = 0.48 * ) and directly and closely correlated in the period from July to January (r = 0.99 ** ). Amylase activity was significantly and directly, but not closely, correlated with soil ammonium-N content (r = 0.43 * ) and with leaf dry matter (r = 0.41 * ). A rainy period of five days was sufficient to increase saccharidase activity in the soil.