Flow volumes and NO 3 -N concentrations of drain discharge from five systematically tiled, commercial potato (Solatium tuberosum L.) fields were measured from April to December, 1987 and 1988, to assess the potential for NO 3 -N leaching associated with current production practices. The sites, located in New Brunswick, Canada, ranged from 3 to 10 ha and varied in fertilizer application rate, cropping practices, rainfall, and duration of data collection (the latter due to site access difficulties in the spring). Three of the five sites were representative of intense potato rotations, whereas the remaining two were representative of land conversions into potato production from more passive, low input production systems. Ten site-years of data were collected. Drain outflow volumes averaged 75 and 115 mm per unit area in 1987 and 1988, respectively. Considerable drain flow occurred during snowmelt each year before data collection began. Measured NO 3 -N concentrations ranged from 1 to 65 mg L" 1 and there were substantial changes in NO 3 -N concentrations within flow events. The flow-weighted average annual nitrate concentrations of the drainage effluent, (NO 3 -N)|,, were > 10 mg L ' for potato site-years, regardless of whether the sites were established potato rotation fields or not. The (NO 3 -N)J concentrations of the established potato rotation sites also remained >10 mg L ' for the first non-potato year following potato. The (NO 3 -N)£ concentration of one potato rotation site was more than double that of the other two potato rotation sites. Incubation studies showed the soil at this site had considerably more potential to mineralize N than the other two sites. Total NO 3 -N leaching for the potato site-years for the measured April to December periods ranged from 5 to 33 kg N ha '. More work, under controlled conditions, is required to determine both dormant and growing season NO 3 -N leaching associated with various potato production systems.
Total iron and manganese was determined on concretions and soil samples by X‐ray emission. Soils studied included Maury, Mercer, and Lawrence, which are well‐drained, moderately well‐drained and somewhat poorly‐drained, respectively. Iron‐Manganese concretions were observed in all horizons, with a maximum of 46% by weight in a Maury C horizon. The Fe/Mn ratios decreased with increasing concretion size. This decrease was largely due to increased Mn content associated with the larger size concretions. Further analyses for composition showed that quartz and clay minerals (vermiculite, montmorillonite, kaolinite, and mica) account for most of the remaining fractions. Traces of titanium and phosphorus were also found. Microscopic studies of the concretions indicated two types of internal fabric; (i) undifferentiated (structureless), and (ii) differentiated or concentric structure. Concretions from the somewhat poorly drained soils are characterized by undifferentiated fabric and diffuse external boundaries. In contrast the concretions from the well‐drained soils are usually spherical, with sharp external boundaries and differentiated fabric.
Distribution of fixed and exchangeable ammonium were examined in three soil profiles of the Shrouts series from the Knobs region of eastern Kentucky. Shrouts soils (fine, mixed, mesic, Typic Hapludalfs) have high base status; exhibit strong, prismatic structure; and are derived from calcareous, high magnesium, soft (weakly cemented) clay shale. Soil pH ranges from 6.3 in the Ap horizon to 7.9 in the C. Analyses, using the Silva and Bremncr procedure, showed considerable fixed NH 4 *-N in all horizons of each profile. Mean fixed NH t +-N in the profiles was 365 ppm for the Ap, 463 ppm for the B21t, 433 ppm for the B22t, 469 ppm for the C, and 543 ppm for the Cr horizons. Exchangeable NH 4 +-N also increased with depth, with values being about 1.2 to 1.5% of the fixed NH t *-N values. X^ray diffraction analyses of the clays and silts revealed predominantly mica in the 2-0.2 and <0.2 /an fractions, with some vermiculite present, and large quantities of mica in the silt fractions. High correlation (r = 0.92) was found between fixed NH 4 +-N and exchangeable NH/-N. A correlation exists between fixed NH 4 +-N and mica + vermiculite content with an r value of 0.68. The fixed NH 4 +-N in the lower horizons is presumed to be indigeous, since no NH 4 +-N has been added recently to the soil.
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