The Iowa wine and grape industry underwent a rapid phase of growth at the turn of the 21 st century that is continuing to evolve and develop today. Cultivar trials across the state found that 'Marquette' grapevines were performing poorly in eastern Iowa while other cultivars performed well. A preliminary investigation suggested a magnesium induced potassium deficiency and/or above optimum soil pH as the cause of poor growth of 'Marquette'. Soils in the upper Mississippi Valley are derived from limestone and dolomite bedrock resulting in their characteristically high pH and high magnesium properties, which often inhibits potassium uptake. Recommendations to amend these soil types for grape production do not exist but are essential for optimizing grapevine yield. This study was undertaken to determine how to amend vineyard soils with a low potassium/magnesium concentration and above optimum pH. The multi-year pot culture study included two cultivars, Marquette and St. Croix, and four soil amendment treatments. Soil amendment treatments compared all combinations of potassium/magnesium concentration (0.24 and amended to 0.50) and soil pH (7.2 and amended to 6.2) in a two-by-two factorial. Results indicated potassium additions increased the soil potassium/magnesium concentration as well as increased the petiole potassium concentration. Decreasing the pH alone decreased available soil magnesium but had no effect on the potassium/magnesium concentration. This suggests that it is only necessary to add potassium to increase the potassium/magnesium concentration in these soils.

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Agricultural water is a known vector for the transfer of foodborne pathogens onto fresh produce. Development of pre-harvest and post-harvest microbial profiles of agricultural water used by fresh produce growers, processors, and holdings is a requirement under the Food Safety Modernization Act Produce Safety Rule. One of the United States Environmental Protection Agency (US EPA) approved agricultural water testing methods is US EPA Method 1603, which requires no greater than a 6-h time frame between the collection of the water sample and initiation of analysis. This 6-h timeframe is unrealistic for many produce growers due to there being few laboratories certified to conduct testing and the geographic location of the farms. Agricultural water samples (n = 101) from well water and surface water were collected from 60 different farms to determine if holding samples for 24 h yielded significantly more generic Escherichia coli (E.coli) than 6 h using EPA 1603 method. A total of 32 samples were found contaminated with generic E. coli. Of these positive samples, surface water accounted for 87.5% of the samples (n = 28). There was no significant disparity between populations of generic E. coli at 6- and 24-h sample-test time interval (p > 0.05). These results provide evidence that the sample-test time interval can be extended to 24-h time, which makes quantitative generic E. coli testing for agricultural water as mandated by the FSMA Produce Safety Rule more accessible to growers.

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