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.
NITROGEN AND CHLORIDE DISTRIBUTION AND BALANCE IN A CLAY LOAM SOIL
In field experiments conducted on a poorly drained clay loam soil from 1974 to 1976, inclusive, 21–44% of added chloride was lost from the 0- to 75-cm layer by the end of September, whereas NO3−-N increased in this layer in both the control and fertilized plots. Mineralization during the summer masked any N losses by leaching or denitrification. N losses were highest between late fall and early spring. NO3−-N and chloride tended to show similar distribution patterns in the profile but not necessarily similar leaching losses, since simultaneous denitrification occurred in an adjacent experimental site. Chloride distribution in the profile and leaching losses did not appear to coincide with expectations of typical transport theory, since losses were associated with diffuse bulges near the surface instead of distinct peaks or slugs of chloride moving steadily downward.
Spatial distribution of root lesion nematodes (Pratylenchus spp.) in a long-term no-till cropping system and their relationship with soil and landscape properties
The Cook Agronomy Farm of Washington State University is a long-term precision agriculture study site. Since 2000, the farm has been in various three-year no-till rotations with winter wheat, spring wheat, and various rotation crops such as barley, canola, peas, lentils, and chickpea. The spatial distribution of root lesion nematodes (Pratylenchus spp.) and their relationships with soil and terrain variables were studied by collecting soil samples at 127 and 124 geo-referenced points in two 12-ha fields during the spring of 2010 and 2011, respectively. Pratylenchus spp. were detected in more than 85% of the sampled locations in both fields. Nematode densities spatially mapped using ArcGIS software occurred in an aggregated pattern. Previous rotation crops had no effect on the spatial distribution. Classification and regression tree analysis (CART) using soil and terrain variables, and nematode density, explained 61 and 34% of the variability associated with nematode density in 2010 and 2011, respectively. Soil edaphic factors, such as organic matter, were stronger predictors of nematode populations than rotation effects.