Micronutrient content in sugar-cane ash and its effect on a sugar-cane agroecosystem

The zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe) ash contents of two sugar-cane varieties (PR 1028 and V 58-4) cultivated in the Rio Yaracuy Valley (Venezuela) were chemically analyzed. In both varieties of sugar-cane, a great similarity in the amounts of micronutrients extracted was noticed within the various fraction forms. A high element recovery was also obtained and the results indicated that the fractionation method was adequate to extract Zn, Cu, Mn, and Fe from the sugar-cane ashes. About 281 g Zn ha(-1) year(-1); 127 g Cu ha(-1) year(-1); 611 g Mn ha(-1) year(-1) and 6662 g Fe ha(-1) year(-1) were returned annually to the soil by ash deposited in the sugar-cane agrosystem. According to the results of the procedure used, a minor micronutrient ash-fraction would be easily available for the plants. The information suggests that the ashes contained an important part of the agroecosystem micronutrients, affecting soil fertility. Soil chemical analysis can be used as a tool in understanding the role of plant ashes in the nutritional state and micronutrients cycling of agroecosystems where fire is a management practice.