We investigated the effects of variation in ambient air temperature on seed production in the field during the reproductive development phase of `Salinas' head-type lettuce (Luctuca sativa L.) in the central San Joaquin Valley of California where daytime maxima may exceed 38C for many consecutive days during reproduction. Florets were tagged daily for 41 days and harvested seeds were sampled to determine temperature-sensitive periods during seed development. The number of seeds per inflorescence (NOS), seed mass (SM), and seedling root length (SRL) were reduced and percentage germination (GERM) increased with increasing minimum (LT) and maximum (HT) temperatures. Daily HT > 35C greatly reduced NOS. Increasing LT reduced SM and SRL, but to a lesser extent than NOS (r2 = 0.23 and 0.40; P = 0.01 and 0.001, respectively). The advantage of increasing HT on GERM (r2 = 0.20; P = 0.01) was overshadowed by the severe reduction in NOS and the vigor components SM and SRL. The periods of greatest sensitivity to high air temperature for NOS, SM, GERM, and SRL were - 1 to +1, - 4, +1, and - 4 to - 3 days from anthesis, respectively. The hours of peak sensitivity for these variables occurred during the same days at - 36, - 101, + 15, and - 83 hours from anthesis, respectively. Using Box-Jenkins time series analysis, diurnal periodicity in temperature sensitivity for the four variables was determined.
J.J. Steiner and K. Opoku-Boateng
J.O. Payero, M.S. Bhangoo, and J.J. Steiner
The effects of six applied N treatments differing by rates and frequencies of application on the yield and quality of pepper (Capsicum annuum var. annuum L. `Anaheim Chili') grown for seed was studied. The timing of N applications was based on crop phenology, leaf petiole nitrate-nitrogen concentrations (NO3-N) minimum thresholds, and scheduled calendar applications of fixed amounts of N. Solubilized NH4NO3 was applied through a trickle-irrigation system to ensure uniform and timely applications of N. Rate of mature (green and red) fruit production was unaffected by any treatment except weekly applications of 28 kg·ha-1 of N, which stopped production of mature fruit before all other treatments. Early season floral bud and flower production increased with increasing amounts of N. The two highest total N treatments produced more floral buds and flowers late in the season than the other treatments. Total fruit production was maximized at 240 kg N/ha. Differences in total fruit production due to frequency of N application resulted at the highest total N level. Red fruit production tended to be maximized with total seasonal applied N levels of 240 kg·ha-1 and below, although weekly applications of N reduced production. Total seed yield was a function of red fruit production. Pure-1ive seed (PLS) production was a function of total seed production. Nitrogen use efficiency (NUE) for red fruit production also decreased with N rates >240 kg·ha-1, but PLS yield and NUE decreased in a near-linear fashion as the amount of total seasonal applied N increased, regardless of application frequency. Season average NO3-N (AVE NO3-N) values >4500 mg·kg-1 had total seed and PLS yields less than those treatments <4000 mg·kg-1. Six-day germination percentage was reduced with weekly N applications of 14 kg·ha-1. Seed mass was reduced with weekly N applications of 28 kg·ha-1. Final germination percent, seedling root length and weight, and field emergence were unaffected by any of the N treatments. These findings indicate that different N management strategies are needed to maximize seed yield compared to fruit yield and, therefore, there may be an advantage to growing `Anaheim Chili' pepper specifically for seed.
J. J Steiner and D. C. Akintobi
A study was undertaken to determine the moisture content at which the seed of ‘Sweet Spanish’ onion (Allium cepa L.) expressed maximum yield and viability but at the same time did not shatter. A harvest maturity curve was developed to provide an estimate for optimum time of harvest. Umbels could be harvested with moisture contents as high as 66% without any adverse effect on seed size or viability. The umbels could be left on the plant until umbel moisture was as low as 52% before shattering commenced. The resulting 14% moisture range, within which harvest may proceed without losses to shattering or immature seed, provides an adequate buffer for harvesting onion seed.
Frank J. Dainello, Larry Stein, Guy Fipps, and Kenneth White
Competition for limited water supplies is increasing world wide. Especially hard hit are the irrigated crop production regions, such as the Lower Rio Grande Valley and the Winter Garden areas of south Texas. To develop production techniques for reducing supplemental water needs of vegetable crops, an ancient water harvesting technique called rainfall capture was adapted to contemporary, large scale irrigated muskmelon (Cucumis melo var. reticulatus L.) production systems. The rainfall capture system developed consisted of plastic mulched miniature water catchments located on raised seed beds. This system was compared with conventional dry land and irrigated melon production. Rainfall capture resulted in 108% average yield increase over the conventional dry land technique. When compared with conventional furrow irrigation, rainfall capture increased marketable muskmelon yield as much as 5355 lb/acre (6000 kg·ha-1). As anticipated,the drip irrigation/plastic mulch system exceeded rainfall capture in total and marketable fruit yield. The results of this study suggest that rainfall capture can reduce total supplemental water use in muskmelon production. The major benefit of the rainfall capture system is believed to be in its ability to eliminate or decrease irrigation water needed to fill the soil profile before planting.
D.I. Leskovar, L.A. Stein, and F.J. Dainello
This study was conducted to determine the effect of within-row plant spacing and mulching on growth, quality, and yield of an experimental semi-savoy spinach (Spinacia oleracea L.) genotype `Ark-310' to produce a high-quality fresh-market product. Spinach transplants were established in the field on 13 Nov. 1995 and 3 Dec. 1997. Within-row spacings were 15 and 25 cm, and mulching treatments were bare-soil and black polyethylene mulch. Plants were destructively sampled weekly (1996) or bi-weekly (1998) for leaf area (LA), leaf number, leaf dry weight (LDW); and root dry weight (RDW) measurements. Plants grown on plastic mulch at 25-cm spacing had the greater LA, LDW, and RDW than when grown at 15-cm spacing on mulch or bare-soil. Leaf number and specific leaf area (LA/LDW) were less affected by either spacing or mulching. The amount of soil on harvested leaves was lowest on plants grown on plastic mulch in both years. In one year, total yields (MT/ha) were 42% higher when plant spacing decreased from 25 cm to 15 cm, while mulch increased yields by 20 %, a response that was independent of plant spacing. These effects were not evident in the year with higher rainfall. It appears that for a root-cut or loose leaf spinach, yield efficiency and product cleanliness of `Ark 310' spinach may be further improved by combining high plant density with efficient irrigation and fertilization programs under mulch and drip.
Daniel I. Leskovar, Larry A. Stein, and Frank J. Dainello
The objective of this work was to determine the effect of within-row plant spacing and mulching on growth, quality, and yield of an experimental semi-savoy spinach (Spinacea oleracea L.) genotype `Ark-310' to produce a high quality fresh market product. Within-row spacings were 15 and 25 cm, and mulching treatments were bare-soil and black polyethylene mulch. Plants were destructively sampled weekly (1995-96) or bi-weekly (1997-98) for leaf area (LA), leaf number, leaf dry weight (LDW) and root dry weight (RDW) measurements. Plants grown on plastic mulch at 25-cm spacing had greater LA, LDW, and RDW than when grown at 15-cm spacing on mulch or bare-soil. Leaf number and specific leaf area (LA/LDW) were less affected by either spacing or mulching. The amount of soil on harvested leaves was lower on plants grown on plastic mulch in both years. In one year, total yields (MT/ha-1) were 42% higher at 15-cm than at 25-cm plant spacing, while mulch increased yields by 20%, independently of plant spacing. These effects were not evident in the year with higher rainfall (1997-98).
Jeffrey J. Steiner and Benjamin F. Letizia
A major difficulty in conducting seed production research with fleshy-fruited vegetables [e.g., pepper (Capsicum annuum L.), tomato (Lycopersicon esculentum L.), and cucumber (Cucumis sativus L.)] is recovering and cleaning the seeds. Once seeds have matured within the fruit, it is necessary to crush the fruit and extract the seeds from the pulp.
Larry A. Stein and J. Benton Storey
Adjuvants at various concentrations were evaluated for phytotoxicity and capacity to enhance foliar absorption of N and P. Some adjuvants among the following classes were phytotoxic to soybean (Glycine max Merr.) leaves at concentrations of 0.25% and 0.5% active ingredient on a volume or weight/volume basis: sulfonates, alcohols, ethyoxylated hydrocarbons, esters, sulfates, and amines. Many adjuvants in the following classes: alcohols, sulfonates, ethoxylated hydrocarbons, polyethylene glycols, carbohydrates, proteins, and phosphates were not phytotoxic at concentrations as high as 1.0%. Sometimes increasing phytotoxicity occurred at increasing concentrations, but the humectants, such as glycerol and propylene glycol, were not phytotoxic at concentrations of 10.0%. Selected adjuvants were mixed with a foliar fertilizer (12.0N–1.7P–3.3K–0.5S) and evaluated for enhancement of foliar absorption of N and P. The average increases in percentage of N and P for the glycerol, lecithin, and Pluronic L-121 (an ethyoxylated hydrocarbon), and foliar fertilizer combinations, respectively, were 8.9%, 2.2%, and 2.5% for N and 34.2%, 27.6%, and 20.8% for P over the foliar fertilizer control, respectively, for the 3 adjuvants.
R.B. Hutmacher, J.J. Steiner, J.E. Ayars, A.B. Mantel, and S.S. Vail
The influence of irrigation frequency and the severity and rate of development of soil water deficits on the vegetative growth and water status of carrots (Daucus carota L. var. sativa DC.) grown for seed were investigated in a fine sandy loam soil. Beginning with the period of rapid development of primary umbels, various irrigation frequencies [daily vs. intervals corresponding to 30 mm of accumulated crop evapotranspiration (ETc)] were investigated at irrigation rates ranging from 40% to 120% of estimated ETC. The magnitude and rate of development of soil water deficits markedly influenced carrot responses to developing water deficits. Stomata] conductance and leaf water potential (LWP) measurements exhibited some potential for use in irrigation scheduling and were the most sensitive and consistent indicators of plant water status. Under low-frequency continuous-deficit irrigation, a combination of moderate reductions in stomatal conductance and major reductions in peak leaf area and late-season maintenance of viable leaf area occurred. These responses were effective water-conserving mechanisms, allowing growth at a reduced rate and continued development of viable seed. In contrast, rapid development of soil water deficits resulted in nearly complete stomatal closure, cessation of growth, and rapid reductions in leaf area.
J.J. Steiner, R.B. Hutmacher, A.B. Mantel, J.E. Ayars, and S.S. Vail
Seed yield and quality of carrot (Daucus carota var. sativa DC.) were influenced by a wide range of water application regimes and levels. Irrigation treatments were imposed beginning at the time of extension of the primary umbel and extending throughout the reproductive development period. The three application regimes used were: 1) a high-frequency, low water deficit treatment [100% of daily accumulated crop evapotranspiration (ETc)]; 2) a series of five low-frequency (irrigated after 30 mm of accumulated ET,) application treatments with a range of water deficits from moderate to minimal (40% to 120% of ETc applied); and 3) a series of three treatments that had rapidly developing water deficits applied by terminating irrigation at 7, 5, and 2 weeks before harvest after being grown under low-stress conditions. Pure live seed (PLS) yield was optimized by different treatments within each of the three application regimes. Maximum yields were achieved with short-term (2-week) rapidly developing water deficits near harvest, moderate deficit irrigation with 60% to 80% of ETc applied after 30 mm of ETc, or with a low water deficit, high-frequency application. Seed germination percentage decreased as the amount of applied water increased. This effect was more pronounced in the later-developing umbel orders. However, seed quality measured as seedling root length was improved with increasing water application.