SUGAR CANE NUTRIENT REQUIREMENTS AND THE ROLE OF ATMOSPHERIC DEPOSITIONSUPPLYING SUPPLEMENTARY FERTILIZATION IN A VENEZUELAN SUGAR CANE PLANTATION

Abstract

Acidic rains, as a consequence of the high industrial and agricultural activities and loaded with pollutants including nutrients are characteristic of Northern Central Venezuela, a region dominated by sugar cane plantations. Canopies of forest and agricultural crops can modify the chemistry of rainfall: through uptake, leaching and outwash of deposited ions. This paper describes the change in the chemistry of acid rains after passing through a sugarcane canopy. Four plots of 300 m² within a 4.5 ha experimental area, planted with Saccharum officinarum had rain and throughfall collectors installed. The study corresponds to the analysis of the growing season of the third ratoon. The pH of the rain in the agro system increased after passing through the canopy. The magnitudes of the changes were important and partially related to the significant amount of cations leached from the leaves or washed out from dry deposition to the leaves. N inputs for wet and dry deposition in the agro system were high (26.3 kg ha ^-1 yr^-1) as a consequence of the agricultural activity in the area, the local burning of the sugarcane before cropping, and the location of the experimental area close to petrochemical and fertiliser producer industries. Rainfall constitutes an important source of nutrient inputs to the sugar cane system. In the case of the macronutrients (N, P and K), the inputs were high and supply an important fraction of plant nutrient needs, so occurs for zinc and copper.