Robert G. Stevens

Relationship between Soil Temperature and N Release in Organic and Conventionally Managed Vineyards

Soil temperature is a very easily measured parameter that influences nutrient availability in vineyards. We monitored soil temperature and plant-available nitrogen (N) in a study evaluating the potential of legumes as an interrow cover crop to supply N to Concord grape (Vitis labruscana Baily). Nitrogen sources used were hairy vetch (Vicia villosa subsp. villosa L.) and yellow sweet clover [Melilotus officinalis (L.) Lam] as green manure sources and either blood meal (in a certified organic vineyard) or urea (in a conventional vineyard) as soluble sources. Plant-available N was measured both continuously using ion exchange membranes (PRSTM) and point in time by soil sampling at regular intervals; both were analyzed for nitrate (NO3) N and ammonium (NH4) N, although negligible concentrations of NH4-N were detected. PRS NO3-N concentration varied by treatments because of differences in the chemical composition of the N source. Soil NO3-N concentration reached a peak between 520 and 550 degree-days with no significant differences by treatment or site. These findings are similar to results from incubation and field mineralization studies of organic amendments and suggest that N availability from organic sources in vineyards can be predicted using a degree-day-type model.

Evaluation of yield quantity and quality of two oil crops in the promotion of sustained deficit irrigation in the Pacific Northwest, USA

Agriculture, as the main user of available fresh water in the Pacific Northwest, faces persistent pressure to be efficient. The intent is to maximize the water use efficiency of crops by minimizing the amount of water used for production by reducing irrigation levels and minimizing water losses. This study evaluated the impacts of reduced, sustained deficit irrigation water management on two specialty oil crops, mint and canola. The study evaluated the yield parameters of native spearmint (Mentha Spicata) and two varieties of canola (Rapier and Athena) over two seasons for the impact of sustained deficit irrigation on the quantity and quality of yields and yield characteristics. Sustained deficit irrigation is shown to be adaptable to water constraints for canola and spearmint with potentials to stabilize farm returns by potentially raising the unit price of the oils and byproducts. With this scenario increased price offers, due to improved quality coupled with production cost savings would create a production niche to sustain the Pacific Northwest spearmint and canola farming systems.