Ammonia loss significantly reduces the urea-N use efficiency in crop production. Efforts to reduce this problem are mostly laboratory oriented. This paper reports the effects of urea amended with triple superphosphate (TSP) and zeolite (Clinoptilolite) on soil pH, nitrate, exchangeable ammonium, dry matter production, N uptake, fresh cob production, and urea-N uptake efficiency in maize (Zea mays) cultivation on an acid soil in actual field conditions. Urea-amended TSP and zeolite treatments and urea only (urea without additives) did not have long-term effect on soil pH and accumulation of soil exchangeable ammonium and nitrate. Treatments with higher amounts of TSP and zeolite significantly increased the dry matter (stem and leaf) production of Swan (test crop). All the treatments had no significant effect on urea-N concentration in the leaf and stem of the test crop. In terms of urea-N uptake in the leaf and stem tissues of Swan, only the treatment with the highest amount of TSP and zeolite significantly increased urea-N uptake in the leaf of the test crop. Irrespective of treatment, fresh cob production was statistically not different. However, all the treatments with additives improved urea-N uptake efficiency compared to urea without additives or amendment. This suggests that urea amended with TSP and zeolite has a potential of reducing ammonia loss from surface-applied urea.
Nitrogen (N) transport from land to water is a dominant contributor of N in estuarine waters leading to eutrophication, harmful algal blooms, and hypoxia. Our objectives were to (1) investigate the composition of inorganic and organic N forms, (2) distinguish the sources and biogeochemical mechanisms of nitrate-N (NO3-N) transport using stable isotopes of NO3- and Bayesian mixing model, and (3) determine the dissolved organic N (DON) bioavailability using bioassays in a longitudinal gradient from freshwater to estuarine ecosystem located in the Tampa Bay, Florida, United States. We found that DON was the most dominant N form (mean: 64%, range: 46-83%) followed by particulate organic N (PON, mean: 22%, range: 14-37%), whereas inorganic N forms (NOx-N: 7%, NH4-N: 7%) were 14% of total N in freshwater and estuarine waters. Stable isotope data of NO3- revealed that nitrification was the main contributor (36.4%), followed by soil and organic N sources (25.5%), NO3- fertilizers (22.4%), and NH4+ fertilizers (15.7%). Bioassays showed that 14 to 65% of DON concentrations decreased after 5-days of incubation indicating utilization of DON by microbes in freshwater and estuarine waters. These results suggest that despite low proportion of inorganic N forms, the higher concentrations and bioavailability of DON can be a potential source of N for algae and bacteria leading to water quality degradation in the estuarine waters.
This study was conducted to: (1) assess the role of wetland vegetation in the removal of oxygen demand and nitrogen under tropical conditions, (2) estimate the uptake of nitrogen and copper by wetland plants and (3) investigate the speciation of Cu in wetland media among four operationally defined host fractions, namely exchangeable, carbonate, reducible and organically bound. Four laboratory-scale wetland units, two free-water-surface (FWS) and two subsurface-flow (SF) with one of each planted with cattails (Typha augustifolia), were fed with primary-treated sewage and operated at nominal retention times of 0.6-7 days. The influent and effluent BOD/COD and nitrogen concentrations were monitored to assess the performance of the wetland units for various mass loading rates. At the end of the study, all cattail plants were harvested and analyzed for total Kjeldahl nitrogen (TKN). Four other wetland units, which were identical to the first four, were fed with domestic wastewater spiked with copper in increasing concentrations. Copper speciation patterns in the sand layer were determined at the end of the study. The results showed that wetland vegetation did not play an important role in oxygen demand removal but were capable of removing about 22% and 26% of the nitrogen input in the FWS and SF wetland units, respectively. Mass balance analysis indicated that less than 1% of copper introduced was taken up by the cattails. Copper speciation patterns in the sand media showed that the exchangeable fraction contributed 30-57% and 63-80% of the nonresidual copper in the planted and unplanted FWS wetlands, respectively. For SF units, the percentages were 52-62% and 59-67%, respectively. This indicates that large amount of copper in the media were potentially remobilizable.