Efficacy and Cost of Cultivators, Steam, or an Organic Herbicide for Weed Control in Organic Vineyards in the San Joaquin Valley of California

Weed management is an important problem faced by organic grape (Vitis vinifera) growers as there are few effective and economic options available. However, new organically acceptable weed control products have become available in recent years. Several studies were conducted to compare the efficacy of two mechanical weed control methods (French plow and Bezzerides tree and vine cultivator) with steam, and an organic herbicide (d-limonene) in organic raisin and wine grape vineyards. The experiments were designed as split plots with the aforementioned treatments as main plots with additional weed control treatments (handhoeing and no handhoeing in the raisin grape vineyards; hoeing, no hoeing, steam, and d-limonene in the wine grape vineyard) one month after the main plot treatment as subplots. The plow provided the greatest level of weed control among the treatments followed by the cultivator. The time required to hoe mechanically cultivated plots was also generally lower than the other treatments. Steam and herbicide only suppressed weeds for 2–3 weeks, and the time needed to hoe plots in these treatments was generally similar to the untreated control at all sampling dates. The mechanical treatments also were two to four times more cost-effective than steam or herbicide. Therefore, mechanical treatments were the most effective and economical weed control methods, though none of the treatments affected vine growth, midday stem water potential, petiole nitrate concentration at bloom, grape yield, or quality.

Preliminary Estimates of Nitrogen Availability from Liquid Dairy Manure to Potato

Within Wisconsin, there is a distinct movement toward dairy herd expansion and consolidation of small farms. These large dairies are considering various land and manure management arrangements with non-livestock farmers, such as potato (Solanum tuberosum) producers to increase their manure management options. This study used a fertilizer equivalence approach to evaluate the availability of nitrogen from dairy manure to potatoes. Nitrogen (N) availability was evaluated in field experiments in 2000 and 2001, conducted in northeast Wisconsin using a moderate and a high liquid dairy manure rate [10,000 and 20,000 gal/acre (93,536 and 187,072 L·ha-1)] compared with results obtained from N fertilizer applied at five rates [0 to 240 lb/acre (269.0 kg·ha-1)]. Availability estimates using the fertilizer equivalence method based on tuber yield, harvested tuber N concentration and uptake, petiole nitrate concentration, and soil nitrate levels resulted in apparent availability of manurial N from 10% to 40%, with an overall average across both years of 29.2%. This level is only slightly less than values typically measured where corn has been used as the test crop. In spite of being more shallow-rooted and perhaps somewhat less efficient in N use it does not appear that adjustments to manurial N availability estimates are warranted when potatoes are grown.

257 LEAF PETIOLE NITRATE AND POTASSIUM LEVELS IN POTTED PLANTS GROWN AT THREE NITROGEN AND POTASSIUM LEVELS

Twelve species of flowering potted plants were grown in a peat-based medium with water soluble fertilizer concentrations of 50, 100, or 200 mg·liter-1 N and K2O. Leaf blade or leaf petiole samples were collected six to eight weeks after planting. Sap was expressed using a hydraulic press and levels of nitrate nitrogen and potassium were determined using Cardy flat sensor ion meters. Petiole nitrate level ranged from 520 to 6300 mg·liter-1 and potassium levels ranged from 870 to 3600 mg·liter-1. The petiole nitrate concentration and change in petiole nitrate levels with changes in media nitrate levels was crop dependent. Leaf blade nitrate and potassium concentrations were lower than leaf petiole concentrations. The relationship of petiole nitrate to final plant fresh and dry mass and appearance at flowering will be presented.

Use of petiole analysis for assessment of vineyard nutrient status in the Barossa district of South Australia

Summary. A study of the petiole nutrient status of cvv. Shiraz, Cabernet Sauvignon and Rhine Riesling (Vitis vinifera) was carried out in 19 vineyards of each in the Barossa Valley, South Australia, during 1979 to 1982. The sampling unit chosen was the petiole of leaves opposite bunches, collected at flowering time. Nitrogen status (assessed as nitrate concentration) varied widely among vineyards and high concentrations of nitrate could be associated with use of organic materials (chicken litter, winery marc) in the vineyards. Phosphorus status was almost invariably higher than necessary. Potassium, magnesium and chloride status were usually high by Californian standards. Of the trace elements, boron was low in 1979 to 1980 in some vineyards, but sufficient in other years. Zinc and manganese were usually present in sufficient quantities. Daily sampling of petioles showed that nutrient levels during the flowering period changed less dramatically in this region than in California. Pre-bloom foliar sprays ofurea with zinc had non-significant effects on petiole nitrate concentration. Differences in nutrient concentrations between the three cultivars were detected in some years. The standards used to interpret petiole analysis data in California, while useful in the survey area, required some modification for local use, and working standards are proposed.

Nitrogen Uptake of Field-grown Cotton. II. Nitrate Reductase Activity and Petiole Nitrate Concentration as Indicators of Plant Nitrogen Status

SUMMARYThe possibility of using seasonal changes in leaf nitrate reductase activity (NRA) as a reliable and sensitive indicator of plant nitrogen (N) status has been investigated in field-grown cotton. These changes were compared with those in nitrate concentration in petioles and variations in soil-N concentration. We conclude that NRA in the uppermost, fully-expanded sympodial leaves may provide a more convenient, sensitive and reliable indicator of plant-N status than measurements of nitrate concentrations in petioles.