Vinyl-film mulch: a practice for sweet potato (Ipomoea Batatas Lam. var. Edulis Makino) cultivation to reduce nitrate leaching
Abstract Under conventional cultivation practices in Southern Kyushu, Japan, a considerable amount of nitrate-N is leached from agricultural fields into ground water. The leaching processes are accelerated by high permeability of the volcanic ash soil, high rainfall and high summer temperatures. The present work was instigated to study the possibilities of controlling nitrate-N leaching by regulating the infiltration of rain water in the soil, the source of percolation below the root zone. Nitrate-N leaching from the root zone of sweet potatoes to deeper soil layers was compared in three treatments: maximum soil surface mulching with 0.03 mm vinyl-film with holes at ridge tops to supply plants with enough soil moisture to meet the crop water requirement (maximum vinly-film mulch, MVM); applications of fertilizer containing a nitrification inhibitor dicyaniamide (DCD); and conventional cultivation practices. NPK compound fertilizer (N 8 P 5.2 K 16.6 ) containing the ammonium form of nitrogen 900 kg·ha −1 and PK compound fertilizer P 8.7 K 16.6 600 kg·ha −1 were applied in the MVM and conventional plots. DCD-fertilizer (N 15 P 6.5 K 12.5 ), maintaining the same rate of absolute N with adjustment of P and K using fused magnesium phosphate (P 8.6 ) and potassium chloride (K 41.5 ), were applied to the DCD plots. MVM increased surface run-off, resulting in least percolation among the treatments. The highest nitrate-N concentration, taken as an average for 2 years, in soil-water periodically sampled throughout the growing period at 210 cm depth below surface, was found 1.8 ppm in MVM, whereas in DCD and in conventional treatments the same was measured as 8.7 and 5.2 ppm, respectively, indicating the lowest level of nitrate leaching to be in the MVM treatment. The highest availability of mineral nitrogen in the root zone of the MVM treatment was confirmed by the highest plant-top-uptake of nitrogen, Leaf Area Index and vine growth. DCD fertilizer did not contribute to the control nitrate-N leaching. There was no significant difference in root yields among the three treatments.
An Attempt to Reduce Nitrate Content in Ground Water Used for Municipal Water Supply by Changing Agricultural Practices
The heavy use of manure and fertilizers has in some parts of Sweden resulted in unacceptable concentrations of nitrate in ground water used for private and municipal water supply. In Halland for example, several of the municipal water supplies have nitrate concentrations close to 50 mg/I. Either anionic exchange or mixing with water with less nitrate are used to reduce the nitrate content in the distributed water. However, some wells have been abandoned because of high nitrate concentrations. In this study an attempt is made to reduce the nitrogen contamination of the ground water at the source. In well recharge areas the agricultural practices are investigated and, if necessary, alterations are proposed to the farmer in order to decrease the nitrogen leaching from the soil profile. The effect of these improvements is continuously studied in soil and ground water. An action plan is proposed for water supplies with dominating arable land in the recharge area.
Nitrification in subalpine balsam fir soils: Tests for inhibitory factors
Previous work has shown that nitrification is negligible in floors of subalpine balsam fir forests but proceeds vigorously in the Al horizon beneath the forest floor. This paper describes a series of experiments designed to determine the causes for lack of NO−3 production in the forest floor. These experiments showed that denitrification was not important and that autotrophic nitrifiers were present. Increases in pH, essential nutrients and inoculum did not enhance nitrification, indicating that an inhibitor rather than a limiting factor was involved. Analysis of forest floor and Al showed that aluminum was present at concentrations greater than those found to inhibit nitrification in culture. Since the Al was actively nitrifying, it seemed unlikely that aluminum was responsible for nitrification inhibition in the forest floor. Finally, a methanol extract of polyphenols from the forest floor was added to the Al significantly reducing nitrification. These experiments suggest that the higher phenolic concentrations are responsible for inhibition of nitrification in the forest floor.