M. LeStrange

Changes in pH, acids, sugars and other quality parameters during extended vine holding of ripe processing tomatoes

BACKGROUND Two important quality attributes of processing tomatoes are pH and titratable acidity. These and other quality attributes can be affected by tomato fruit maturity and over-maturity. We have determined the magnitude of these maturity effects in four processing tomato cultivars commonly grown in California. RESULTS Allowing tomatoes to remain on the vine for up to 4 weeks after ripening resulted in an increase in fruit pH of between 0.01 and 0.02 unit per day for the four cultivars examined. The increase in pH was paralleled by a decrease in titratable acidity, due to a loss of citric acid. Glucose and fructose concentrations also declined with increasing maturity after ripening. Other quality parameters (color, lycopene, total pectin, pectin solubility, and Bostwick consistency) all showed little change. CONCLUSION Vine holding of ripe fruit adversely affects quality, especially pH and titratable acidity. Recent problems with high tomato juice pH encountered by tomato processors in California could be the result of increased average fruit maturity at harvest.

On‐farm monitoring of soil and crop nitrogen status by nitrate‐selective electrode

Abstract Nitrate‐nitrogen concentration in fresh petiole sap, as measured by a portable, battery‐operated, nitrate‐selective electrode, was highly correlated with NO3‐N concentration in dry petiole tissue of broccoli [Brassica oleracea L. (Italica group), r2 = 0.84], celery [Apium graveolens L. var. dulce (Mill.) Pers., r2 = 0.88], lettuce (Lacluca saliva L., r2 = 0.77), pepper (Capsicum annuum var. annuum L., r2 = 0.89), tomato (Lycopersicon esculentum Mill., r2 = 0.83), and watermelon [Citrulius lanatus (Thunb.) Matsum. & Nakai, r2 = 0.88]. This relationship was linear over a wide range of NO3‐N values and was generally unaffected by site, crop, cultivar, or growth stage, provided that petiole tissue analyzed was from recently matured leaves. Sap was analyzed directly without dilution or filtration. The slope of the regression equation differed widely among crops. Selective electrode analysis of NO3‐N concentration of soil solution samples obtained by suction lysimetry was also highly correlated with co...

Evaluation and Economics of a Rotating Cultivator in Bok Choy, Celery, Lettuce, and Radicchio

Abstract A commercial intrarow rotating cultivator was tested for weed removal and impact on hand-weeding times in bok choy, celery, lettuce, and radicchio. The rotating cultivator was tested as an automated crop thinner and weeder in direct-seeded bok choy and lettuce as an alternative to hand-thinning and -weeding. The rotating cultivator utilized machine-vision guidance to align a rotating disk with the crop plant to be saved and to remove weeds and undesired crop plants. The rotating cultivator was compared to a standard interrow cultivator, which could not remove weeds from the plant line. Main plots were cultivator type, rotating, or standard, and subplots were herbicides: pronamide for lettuce or prometryn for celery. Weed densities, hand-weeding times, crop stand, and yields were monitored. Economic analysis was performed on a subset of the data. The intrarow rotating cultivator was generally more effective than the standard interrow cultivator for reducing weed densities and hand-weeding times. However, the rotating cultivator reduced seeded lettuce stands by 22 to 28% when compared to hand-thinning and standard cultivation, resulting in lower yields and net returns. In transplanted celery, lettuce, and radicchio, the rotating cultivator removed more weeds than the standard cultivator, and reduced stands by just 6 to 9% when compared to the standard cultivator. In transplanted lettuce, the rotating cultivator was more precise and did less damage to the crop. Because transplanted crops were larger than the weeds, they were more easily differentiated using this technology. Net returns were therefore similar between the two cultivators. What is needed for celery and leafy vegetables is an effective intrarow weed removal system that reduces or eliminates the need for hand-weeding yet does not reduce yields. The rotating cultivator was developed for transplanted crops, where it performs adequately, but it cannot be recommended in the seeded crops evaluated. Nomenclature: Prometryn; pronamide; bok choy; Brassica rapa L. subsp. chinensis; celery; Apium graveolens L. var. dulce (Mill.) Pers.; lettuce; Latuca sativa L.; radicchio; Cichorium intybus L. Resumen Se evaluó el uso de un cultivador comercial rotativo intra-línea para la eliminación de malezas y su impacto en la deshierba manual en bok choy, apio, lechuga y radicchio. El cultivador rotativo fue evaluado para ralear el cultivo y para deshierbar automáticamente en bok choy y lechuga de siembra directa como alternativa al raleo y a la deshierba manual. El cultivador rotativo fue guiado con una máquina de visión para alinear un disco rotativo con la planta del cultivo que debía ser salvada y para remover las malezas y las plantas del cultivo no deseadas. El cultivador rotativo fue comparado con un cultivador inter-línea estándar, el cual no podía remover malezas de la línea de siembra. Las parcelas principales fueron el tipo de cultivador, rotativo o estándar, y las sub-parcelas fueron herbicidas: pronamide para la lechuga o prometryn para el apio. Se determinó las densidades de malezas, los tiempos de deshierba manual, y los rendimientos. Se realizó un análisis económico en un subgrupo de los datos. El cultivador rotativo intra-línea fue generalmente más efectivo que el cultivador inter-línea estándar para reducir las densidades de malezas y los tiempos de deshierba manual. Sin embargo, el cultivador rotativo redujo el número de plantas de lechuga establecidas en siembra directa en 22 a 28% en comparación con el raleo manual y el cultivador estándar, lo que resultó en menores rendimientos e ingresos netos. En apio, lechuga y radicchio de trasplante, el cultivador rotativo removió más malezas que el cultivador estándar, y redujo el número de plantas establecidas en solamente 6 a 9% cuando se comparó con el cultivador estándar. En la lechuga de trasplante el cultivador rotativo fue más preciso y causó menos daño al cultivo. Los cultivos trasplantados fueron más fácilmente diferenciados usando esta tecnología porque fueron más grandes que las malezas. Los ingresos netos fueron de esta forma, similares entre los cultivadores. Lo que se necesita para el apio, y los vegetales de hoja es un sistema efectivo para la remoción de malezas intra-línea que reduzca o elimine la necesidad de deshierba manual sin reducir los rendimientos. El cultivador rotativo fue desarrollado para cultivos de trasplante, en los cuales se desempeña adecuadamente, pero este no puede ser recomendado para cultivos de siembra directa.