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T.K. Hartz, M. LeStrange and D.M. May

The response of bell pepper (Capsicum annuum L.) to five rates of N fertigation between 0 and 336 kg N/ha was studied at two drip-irrigated sites [Univ. of California, Davis (UCD) and West Side Field Station, Five Points (WSFS)] in California in 1992. Nitrogen application, in the form of a urea: ammonium nitrate mixture (UN-32), was applied in eight (WSFS) or 10 (UCD) equal weekly increments, beginning after transplant establishment. At both sites, fruit yield and mean fruit size peaked at 252 kg N/ha, with additional N retarding crop productivity. Maximum fruit yield was obtained by fertility treatments that maintained petiole NO3-N concentration >5000 μg·g-1 through the early fruit bulking period. Two techniques for monitoring crop N status, designed for field use, were evaluated. There was a close relationship between the NO3-N concentration of fresh petiole extracts, as measured by a portable, battery-operated nitrate selective electrode, and dry tissue analyzed by conventional laboratory technique (r2 = 0.89). Relative chlorophyll concentration, measured nondestructively by a dual-wavelength leaf absorbance meter, was poorly correlated with whole-leaf N concentration (r2 = 0.55). However, the ratio of such chlorophyll readings for a treatment compared to an in-field reference of known N sufficiency (252 kg·ha-1 treatment) showed promise as a technique for identifying N deficiency.

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M. Cantwell, G. Hong, R. Voss, D. May and B. Hanson

Garlic (cv California Late) was produced under four irrigation regimes (110% and 130% evapotranspiration with two water cut-off dates, 10 and 24 May 1999) in combination with three nitrogen fertilization levels (100, 250, and 400 lb total N). Bulbs were manually harvested mid-June, cured 3 weeks shaded at ambient temperatures and the outer whorl of cloves manually peeled. Samples were freeze-dried, and carbohydrate (fructan and free sugars) and alliin (substrate for alliinase activity and indicator of potential pungency) concentrations were determined by HPLC. The percent dry weight was not affected by the irrigation treatment, but was reduced with increased N rate (41.3% to 39.0%). Alliin concentrations varied from 8.3 to 13.8 mg/g DW for 110% and 130% Eto irrigation treatments. Alliin concentrations were not affected by N fertilization (average = 11.5 mg/g DW). Fructan concentrations were affected by N fertilization treatment, with the highest content (802 mg/g DW) associated with the lowest N level, and the lowest (717 mg/g DW) content in samples from the highest N rate. Sucrose concentrations increased with increased N, but glucose and fructose concentrations did not vary with N fertilization. Fructan as percent of total carbohydrate remained constant across irrigation treatments (96.6% + 0.2%) and across N fertilization treatments (96.6% + 0.3%).

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J.P. Mitchell, D.M. May and C. Shennan

Field studies were conducted in 1992 and 1993 to assess the effects of irrigation with saline drainage water on processing-tomato fruit yields and quality constituents. Saline water (ECiw = 7 dS/m) was used for 66% of the seasonal irrigation requirements in 1992 and 82% in 1993. Yields of tomatoes irrigated with saline water were maintained relative to nonsaline irrigation in 1992, but were decreased by 33% in 1993. Juice Brix and Bostwick consistency were generally improved by irrigation with saline water. pH was unaffected by irrigation treatment, and titratable acidity, an estimate of citric acid content, was increased only in 1993. Calculated quantities for various marketable processed product yields reflect the dominant influence of fresh fruit yield that masked, to a large extent, whatever quality enhancements that may have derived from saline irrigation. The substantial tomato yield reduction that occurred in the second year of this study in plots irrigated with saline drainage water, the gradual surface accumulation of boron, as well as the significant salt buildup in lower portions of the crop root zone following drainage water irrigations demonstrate definitive limitations to the reuse approach and restrict options for the crops that can be grown in this system and the frequency of saline drainage reuse.

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P.R. Johnstone, T.K. Hartz and D.M. May

California melon (Cucumis melo) growers commonly apply calcium (Ca) fertilizers during fruit development to increase fruit firmness and improve storage life. Drip-irrigated field trials were conducted in central California in 2005 and 2006 to evaluate the efficacy of this practice on honeydew (C. melo Inodorus group) and muskmelon (C. melo Reticulatus group). In the 2005 honeydew trial, three weekly applications of 10 lb/acre Ca from calcium nitrate (CN), calcium thiosulfate (CTS), or calcium chloride (CC) were injected into the irrigation system during early melon development. In the 2006 muskmelon trial, two applications of 15 lb/acre Ca from CTS or CC were made early, or two applications of CC late, in melon development. The effect of these Ca fertigation treatments on fruit yield, soluble solids concentration, flesh firmness, and Ca concentration were compared with an untreated control receiving no Ca fertigation. Calcium fertigation had no effect on marketable yield, quality, or Ca concentration of honeydew or muskmelon fruit regardless of application timing or Ca source applied. Loss of firmness during either 2 weeks (honeydew) or 1 week (muskmelon) of postharvest storage was unrelated to Ca fertigation treatment and was not correlated with Ca concentration in fruit tissue. We conclude that under conditions representative of the California melon industry, Ca fertigation at typical application rates is ineffective in improving honeydew or muskmelon yield or fruit quality.

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H.H. Krusekopf, J.P. Mitchell, T.K. Hartz, D.M. May, E.M. Miyao and M.D. Cahn

Overuse of chemical N fertilizers has been linked to nitrate contamination of both surface and ground water. Excessive fertilizer use is also an economic loss to the farmer. Typical N application rates for processing tomato production in California's Central Valley are 150-250 kg·ha-1, and growers generally fail to fully consider the field-specific effects of residual soil NO3-N concentration, or N mineralization potential of the soil. The purpose of this research was to determine the effects of sidedress N fertilizer application, residual soil NO3-N, and in-season N mineralization, on processing tomato yield. Research was conducted during the 1998 and 1999 growing seasons at 16 field sites. Pre-sidedress soil nitrate concentration was determined at each trial site to a depth of 1 m, and aerobic incubation tests were conducted on these soils (top 0.3 m depth) to estimate N mineralization rate. Sidedress fertilizer was applied at six incremental rates from 0 to 280 kg N/ha, with six replications of each treatment per field. Only five fields showed yield response to fertilizer application; yield response to fertilizer was associated with lower pre-sidedress soil nitrate levels. In most fields with fertilizer response, yield was not increased with sidedress N application above 56 kg·ha-1. Mineralization was estimated to contribute an average of ≈60 kg N/ha between sidedressing and harvest. These results suggest that N fertilizer inputs could be reduced substantially below current industry norms without lowering yields, especially in fields with higher residual soil nitrate levels.

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H.H. Krusekopf, J.P. Mitchell, T.K. Hartz, D.M. May, E.M. Miyao and M.D. Cahn

Overuse of chemical N fertilizers has been linked to nitrate contamination of both surface and ground water. Excessive use of fertilizer also is an economic loss to the farmer. Typical N application rates for processing tomato (Lycopersicon esculentum Mill.) production in California are 150 to 250 kg·ha-1. The contributions of residual soil NO3-N and in-season N mineralization to plant nutrient status are generally not included in fertilizer input calculations, often resulting in overuse of fertilizer. The primary goal of this research was to determine if the pre-sidedress soil nitrate test (PSNT) could identify fields not requiring sidedress N application to achieve maximum tomato yield; a secondary goal was to evaluate tissue N testing currently used for identifying post-sidedress plant N deficiencies. Field experiments were conducted during 1998 and 1999. Pre-sidedress soil nitrate concentrations were determined to a depth of 60 cm at 10 field sites. N mineralization rate was estimated by aerobic incubation test. Sidedress fertilizer was applied at six incremental rates from 0 to 280 kg·ha-1 N, with six replications per field. At harvest, only four fields showed a fruit yield response to fertilizer application. Within the responsive fields, fruit yields were not increased with sidedress N application above 112 kg·ha-1. Yield response to sidedress N did not occur in fields with pre-sidedress soil NO3-N levels >16 mg·kg-1. Soil sample NO3-N levels from 30 cm and 60 cm sampling depth were strongly correlated. Mineralization was estimated to contribute an average of 60 kg·ha-1 N between sidedressing and harvest. Plant tissue NO3-N concentration was found to be most strongly correlated to plant N deficiency at fruit set growth stage. Dry petiole NO3-N was determined to be a more accurate indicator of plant N status than petiole sap NO3-N measured by a nitrate-selective electrode. The results from this study suggested that N fertilizer inputs could be reduced substantially below current industry norms without reducing yields in fields identified by the PSNT as having residual pre-sidedress soil NO3-N levels >16 mg·kg-1 in the top 60 cm.

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T.K. Hartz, L.J. Kies, A. Baameur and D.M. May

Application of DCPTA, as a seed treatment and a foliar spray, was evaluated for effects on productivity and fruit quality of processing tomato (Lycopersicon esculentum Mill.) and fresh-market pepper (Capsicum annuum L.). Two field trials for each crop were conducted in California during 1992. No DCPTA treatment was effective in increasing vegetative growth or fresh fruit yield of either crop at any site. Total soluble solids concentration and color of tomato fruits were unaffected by DCPTA, regardless of application method. We conclude that DCPTA is not a useful production aid for field-grown tomato or pepper. Chemical name used: 2-(3,4-dichlorophenoxy) triethylamine (DCPTA).

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J.P. Mitchell, C. Shennan, S.R. Grattan and D.M. May

Effects of deficit irrigation and irrigation with saline drainage water on processing tomato (Lycopersicon esculentum Mill, cv. UC82B) yields, fruit quality, and fruit tissue constituents were investigated in two field experiments. Deficit irrigation reduced fruit water accumulation and fresh fruit yield, but increased fruit soluble solids levels and' led to higher concentrations of hexoses, citric acid, and potassium. Irrigation with saline water had no effect on total fresh fruit yield or hexose concentration, but slightly reduced fruit water content, which contributed to increased inorganic ion concentrations. Fruit set and marketable soluble solids (marketable red fruit yield × percent soluble solids) were generally unaffected by either irrigation practice. Water deficit and salinity increased starch concentration during early fruit development, but, at maturity, concentrations were reduced to < 1%, regardless of treatment. Higher fruit acid concentrations resulted from water deficit irrigation and from irrigation with saline water relative to the control in one year out of two. These results support the contention that deficit irrigation and irrigation with saline drainage water may be feasible crop water management options for producing high quality field-grown processing tomatoes without major yield reductions. Appropriate long-term strategies are needed to deal with the potential hazards of periodic increases in soil salinity associated with use of saline drainage water for irrigation.

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J.P. Mitchell, P.B. Goodell, R. Bader, R. Cifuentes, T.S. Prather, R.L. Coviello and D.M. May

A participatory, on-farm research and extension program has been established around 16 demonstration comparisons of biologically integrated soil building–pest management systems and conventionally managed systems within the West Side row crop area of California's San Joaquin Valley. In each of the biologically integrated parcels, cover crops and composted organic materials are integrated into rotations wherever appropriate, whereas in the conventionally managed parcels, mineral fertilizer applications are made. Pest management practices are evaluated and biologically and informationally intensive alternatives are developed through a participatory process. Indices of soil quality including nutrient status, water stable aggregates, organic matter content, and phospholipid fatty acids are routinely monitored. Information related to the objectives, structure and monitoring activities of this project during the establishment phase will be discussed.

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J.P. Mitchell, P.B. Goodell, T.S. Prather, R.L. Coviello, T.K. Hartz, K.J. Hembree, D.S. Munk, D.M. May, F. Menezes, K. Grimes, J. Diener and T. O'Neill

In Fall 1995, 12 row crop farmers in conjunction with Univ. of California, NRCS and private agency advisors established the West Side On-Farm Demonstration Project to conduct demonstrations of soil and pest management options aimed at sustained profitability and environmental stewardship in the western San Joaquin Valley of California. Monitoring of soil physical, chemical, and biological properties is done in side-by-side on-farm comparisons of plots amended with organic inputs and unamended plots. Intensive monitoring of beneficial and pest insects is carried out within each comparison block, and the data generated is used to guide pest management decision-making at each site. Yields and soil characteristics of the amended plots did not differ from those of unamended plots after the first year. The on-farm context and the cooperative farmer–scientist interactions of this project facilitate the development of timely and relevant research directions to be pursued beyond the core set of monitoring activities.