No abstract

Effectiveness of vegetative buffer strips for herbicide retention from agricultural runoff was evaluated in a twoyear natural rainfall study. A source area of 0.41 ha (mainly Canisteo silty clay loam soil), having an average slope of 3%, was fall chisel-plowed, spring disked, and planted to corn. Three herbicides (atrazine, metolachlor, and cyanazine) were applied to the source area in each spring. Six vegetative buffer strips, 1.52 m wide ¥ 20.12 m long, were isolated with metal borders downslope of the source area in a well established bromegrass (Bromus inermis) waterway. These strips provided for three replications of two drainage to buffer area ratio treatments of 15:1 and 30:1. Herbicide retention was dependent on the antecedent moisture conditions of the strips. These retentions ranged from 11 to 100% for atrazine, 16 to 100% for metolachlor, and 8 to 100% for cyanazine. Herbicide retention by the buffer strips for the two treatments were not significantly different for the observed storm events. Herbicide concentrations in solution in outflow from the strips were less than the inflow concentrations for all the three herbicides. Infiltration was the key process for herbicide retention by the buffer strips, although there was some adsorption to in-place soil and/or vegetation. Metolachlor concentrations in sediment increased in outflow for the two treatments; however, the opposite was true for atrazine and cyanazine. Herbicide retention by sediment deposition in the strip represented about 5% of the total herbicide retention by the buffer strips. The buffer strips were found to have high percent sediment retention, ranging from 40 to 100%; thus, the strips would be more effective for retaining strongly adsorbed herbicides.

The volumes and NO3‐N contents of tile drainage from two plots grown to corn (Zea Mays L.) in rotation with either oats (Avena sativa L.) or soybeans (Glycine max (L.) Merr.) for 1974–1978 were measured to determine the effect of differential N fertilization on NO3‐N leaching losses. The plots, grown to corn and fertilized in even‐numbered years only, were fertilized with N at rates of 100 and 250 kg/ha in 1974 and 90 and 240 kg/ha in 1976. In 1978, both plots were fertilized with 90 kg N/ha. The NO3‐N contents of tile drainage from these plots had been established in a previous 4‐year study in which both plots received 112 kg N/ha in 1970 and again in 1972. These data provided a means of comparison on both an absolute and a relative basis for this second phase of a “before and after” study.Although the ratios of NO3‐N concentrations in daily samples from the two plots in phase one were constant and near unity, after differential fertilization, concentrations for the higher fertility plot exceeded those of the lower fertility plot for extended periods by a factor of two after the 1974 fertilization, and by a factor of four after the 1976 fertilization. In 1974, there was a delay of about 2 months (100 mm of flow) before the effect of surface fertilization was observed in the tile drainage; a similar delay was observed in 1976. Although relative NO3‐N concentrations for the higher fertility plot eventually decreased with time after the last differential fertilization, grab samples taken 3 years later still showed the effect of the higher level of fertilization. Overall, concentrations and losses for the plot receiving 90–100 kg N/ha every‐other year averaged 20 µg/ml and 27 kg/ha; for the plot receiving the most fertilizer, the values were 40 µg/ml and 48 kg/ha. For the 9 years of record, annual flow volumes averaged 132 mm, which represents a significant contribution to stream flows in central Iowa.

Ochratoxin A is a toxic and carcinogenic fungal secondary metabolite; its presence in foods is increasingly regulated. Various fungi are known to produce ochratoxins, but it is not known which species produce ochratoxins consistently and which species cause ochratoxin contamination of various crops. We isolated fungi in the Aspergillus ochraceus group (section Circumdati) and Aspergillus alliaceus from tree nut orchards, nuts, and figs in California. A total of 72 isolates were grown in potato dextrose broth and yeast extract-sucrose broth for 10 days at 30°C and tested for production of ochratoxin A in vitro by high-pressure liquid chromatography. Among isolates from California figs, tree nuts, and orchards, A. ochraceus and Aspergillus melleus were the most common species. No field isolates of A. ochraceus or A. melleus produced ochratoxin A above the level of detection (0.01 g/ml). All A. alliaceus isolates produced ochratoxin A, up to 30 g/ml. We examined 50,000 figs for fungal infections and measured ochratoxin content in figs with visible fungal colonies. Pooled figs infected with A. alliaceus contained ochratoxin A, figs infected with the A. ochraceus group had little or none, and figs infected with Penicillium had none. These results suggest that the little-known species A. alliaceus is an important ochratoxin-producing fungus in California and that it may be responsible for the ochratoxin contamination occasionally observed in figs.