Atmospheric Nitrogen Deposition can Provide Supplementary Fertilization to Sugar Cane Crops in Venezuela

摘要

Acidic rain, loaded with ammonium is characteristic of Central Northern Venezuela, a region dominated by sugarcane plantations. Nitrogen (N) inputs in precipitation are crucial to the N economy of natural ecosystems; in agro-systems these inputs are of less importance. However, in some polluted areas, atmospheric deposition loaded with N as a consequence of industrial and agricultural activities can contribute significantly to crop nutrition. The N and other nutrients present in both precipitation and dry deposition can originate from a variety of natural and anthropogenic sources, including air pollution. Canopies of forest and agricultural crops can modify the chemistry of rainfall in different ways: through uptake, leaching and removal of ions from the canopy in throughfall. In this contribution we analyzed the chemical changes in N enriched acid rain as it passed through a sugarcane canopy. The study site was located on a sugarcane farm near San Felipe, Yar-acuy state, Venezuela. Four plots of 300 m~2 within an experimental area of 4.5 ha, planted with Saccharum officinarum had rain and throughfall collectors installed. The study corresponds to the analysis of the second and third ratoons of two sugarcane varieties. Rain water was quite acidic ranging from 3.54 to 4.52, a situation that is common in Northern Central Venezuela as a consequence of the high industrial and agricultural activities. The pH of the acid rain in the sugar cane system increased after passing through the canopy. The magnitudes of the changes were important and related to the significant amount of cations leached from the leaves or washed out from dry deposition to the leaves and cane stems. Ammonium was the dominant N form in wet deposition. N inputs for wet and dry deposition in the agro-system were high compared with other ecosystems (26.3 kg ha~(-1) year~1, mostly in the ammonium form). This is probably due to: the high agricultural activity in the area, the local burning of the sugarcane before cropping, and the location of the experimental area close to petrochemical industrial activities and fertilizer producer industries. Although nitrates were leached and wash out in throughfall, the balance accounted for a significant N fertilization of the canopy through ammonium uptake.