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Giovanni Piccinni, Daniel I. Leskovar, and Thomas Marek

Lysimeters are used to measure real-time water use during the growing season. By relating the water use of a specific crop to a well-watered reference crop, such as alfalfa or grass, crop coefficients (Kc) can be developed to assist in predicting accurate crop needs using available meteorological data. Reference evapotranspiration can be obtained from several weather networks; however, without crop coefficients for specific crops, this information is only useful for grass. Three weighing lysimeters, consisting of undisturbed 1.5 m × 2.0 m area by 2.2-m depth cores of soil, comprise the Texas A&M Research and Extension Center–Uvalde lysimeter facility. Two lysimeters, weighing around 15,000 kg, have been placed beneath a linear LEPA irrigation system and used in field production. A third lysimeter measures reference ET values (ETo) and is located in a grassed area near the field lysimeters irrigated by subsurface drip irrigation system. Spinach was grown in one of the two crop lysimeters while onion was grown in the second lysimeter. Daily water use was measured on 5-min intervals. Results show the possibility of saving ≈61 to 74 million m3 of water per year in the irrigated farms of the Edwards aquifer region if proper irrigation management techniques are implemented in conjunction with the newly developed crop coefficients. Crop water requirements, Kc determination, and comparison to existing FAO Kc values will be discussed.

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Daniel I. Leskovar, Giovanni Piccinni, and Darrin Moore

A two-year experiment was conducted to determine yield, water use efficiency, and leaf quality responses to deficit irrigation and plant population of spinach (Spinacia oleracea L.). Three irrigation regimes were imposed with a center pivot system, 100%, 75%, and 50% crop evapotranspiration rates (ETc). Spinach seeds were planted on 11 Nov. 2003 at three plant populations: 494 (P-1), 618 (P-2), and 741 (P-3) thousand seeds/ha on cvs. DMC 16 and ASR 157, and on 15 Oct. 2004 at four plant populations: 655, 815, 988, and 1149 thousand seeds/ha on cv. DMC 16. Harvests were done on 3 Mar. 2004 and 26 Jan. 2005. In the first season, marketable yield was not reduced by deficit irrigation, but water use efficiency was significantly higher for 50% ETc compared to 100% ETc. The cv. DMC 16 had a significantly lower percentage of stem weight than ASR 157 (8.3 vs. 16.4%). The cv. ASR 157 had an excess of stem weight at 100% and 75% ETc compared to 50% ETc at P-1, but similar at P-2 and P-3. The cv. DMC 16 had a trend of reduced stem weight for P3 at 50% ETc. In the second season, marketable yield was reduced by deficit irrigation. However, water use efficiency was significantly higher for 50% ETc compared to 100% ETc, but similar to 75% ETc. Deficit irrigation also decreased the percentage of stem weight. Despite a slight increase in the percentage of of yellow leaves, but not in percentage of of stem weight, marketable yield and water use efficiency were significantly higher at 1149 thousand seeds/ha. This study showed that deficit irrigation in combination with increased plant population has the potential to increase yield and water savings, without adversely affecting leaf quality.

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José A. Franco and Daniel I. Leskovar

Containerized `Lavi' muskmelon [Cucumis melo L. (Reticulatus Group)] transplants were grown in a nursery with two irrigation systems: overhead irrigation (OI) and flotation irrigation (FI). Initially, root development was monitored during a 36-day nursery period. Thereafter, seedling root growth was monitored either in transparent containers inside a growth chamber, or through minirhizotrons placed in the field. During the nursery period, OI promoted increased early basal root growth, whereas FI promoted greater basal root elongation between 25 and 36 days after seeding (DAS). At 36 DAS leaf area, shoot fresh weight (FW) and dry weight (DW), and shoot to root ratio were greater for OI than for FI transplants, while root length and FWs and DWs were nearly the same. Total root elongation in the growth chamber was greater for FI than for OI transplants between 4 and 14 days after transplanting. Similarly, the minirhizotron measurements in the field showed a greater root length density in the uppermost layer of the soil profile for FI than for OI transplants. Overall, muskmelon transplants had greater root development initially when subjected to overhead compared to flotation irrigation in the nursery. However, during late development FI transplants appeared to have a greater capacity to regenerate roots, thus providing an adaptive mechanism to enhance postplanting root development and to withstand transplant shock in field conditions. At harvest, root length density and yield were closely similar for the plants in the two transplant irrigation treatments.

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Maria A. Macias-Leon and Daniel I. Leskovar

In the United States, most short-day onions are direct seeded. With this method, plant stands can be reduced because of extreme temperatures, weed pressure, and soil-borne diseases. Containerized transplants offer an alternative method of stand establishment with less seedling losses while producing uniform bulb sizes and high marketable yield. However, the use of transplants is not a widespread commercial practice because of the high cost of production. This study aims to select the best transplant strategies to improve onion crop performance in semiarid regions of southwest Texas or similar environments. Three sequential transplanting dates of early, mid, and late season (14 Nov., 8 Dec., and 9 Jan.) and two seedling densities of one seed per cell (T1) and three seeds per cell (T3) were evaluated on growth, yield, bulb quality, and phytonutrient content of three onion cultivars, two yellow (‘Caramelo’ and ‘Don Victor’), and one red (‘Lambada’). During early development, late-transplanted onions had an increase in plant height and greater leaf elongation rate than early and midtransplanted onions, whereas early plantings required more days to reach maturity than mid and late plantings. Overall, early and midtransplanting dates resulted in higher yields than late plantings. Although increasing seedling density (T3 vs. T1) did not significantly reduce marketable yield in early plantings, T1 produced a higher number of jumbo and colossal bulb sizes than T3. Onion quality was mostly affected by cultivar and not by transplant strategies. The technique of establishing onions from transplants grown from one plant per cell (T1) or multiple plants (T3) from early November to early December provides a practical and economical alternative to achieve earlier crops, while reducing the length of the production season, as planting date is delayed.

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Brian A. Kahn and Daniel I. Leskovar

Single- and double-row arrangements of a fixed population (one plant every 0.285 m2) were compared in factorial combination with two (2002) or five (2003) cultivars for effects on yield and fruit quality of bell pepper (Capsicum annuum L.). Arrangements for 2002 were S30, single rows 0.95 m apart, plants within rows 30 cm apart; D30, 1.9 m between centers of double-row beds, double rows 30 cm apart on beds, plants within rows 30 cm apart; S37.5, single rows 0.76 m apart, plants within rows 37.5 cm apart; and D37.5, 1.52 m between centers of double-row beds, double rows 24 cm apart on beds, plants within rows 37.5 cm apart. Only the S30 and D30 arrangements were used in 2003 after 2002 results showed almost no differences between S30 and S37.5 or between D30 and D37.5. Choice of cultivar was more critical in Texas, where `X3R Wizard' consistently outperformed `King Arthur', than in Oklahoma. Single rows resulted in more full-season total marketable fruit weight than double rows in three experiments out of four, primarily as a result of an increased weight of U.S. No. 1 fruit with single rows. Average weight per marketable fruit was consistently unaffected by plant arrangement. Single rows also resulted in a greater full-season weight of sunburned fruit than double rows in two experiments out of four. Cultivar × plant arrangement interactions were not evident in Oklahoma and never involved full-season marketable fruit weights at either location in either year. Given the tested population, a single-row arrangement is likely to result in increased full-season production of U.S. No. 1 bell pepper fruit compared with a double-row arrangement, despite an increased potential for sunburned fruit with single rows.

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Daniel I. Leskovar, Daniel J. Cantliffe, and Peter J. Stoffella

Tomato, cv. `Sunny' containerized transplants produced either with overhead (SP1) or sub (flotation) (SP2) irrigation were established in the field in fall, winter, and spring. Leaf area (LA), root volume (RV), and dry weights of shoots (SDW) and roots (RDW) were measured weekly before and after transplanting. In fall 1987, SP1 with 44 cm2 LA, 275 mg SDW, 68 mg RDW, and 0.9 ml RV at transplanting (T0) had 33% more fruit yield than SP2 transplants with 20 cm2 LA, 236 mg SDW, 62 mg RDW, and 0.6 ml RV at T0. In spring and winter 1988, SDW, RDW, and RV increased uniformly in both SP1 and SP2 plants, and yields did not differ significantly. In spring 1989, at T0, SP1 had 182 mg SDW and 7.8 shoot/root ratio (S:R) and SP2 had 92 mg SDW and 4.6 S:R, thereafter SDW and S:R ratios were not different and yields were unaffected. In fall 1989, SP1 total fruit yeild (52.3 t.ha-1) did not differ significantly from that of SP2 (47.4 t.ha-l) plants. Sub irrigated transplants may have similar fruit yields than overhead irrigated transplants provided plants are kept with minimum stress before establishment.

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Daniel I. Leskovar, Daniel J. Cantliffe, and Peter J. Stoffella

Studies were conducted to evaluate growth of tomato (Lycopersicon esculentum Mill.) transplants in the field in response to age of transplants in Spring and Fall 1989. Transplants were 2 (2W), 3 (3W), 4 (4W), 5 (SW), or 6 (6W) weeks old. Drip and subseepage irrigation were used. In spring, older transplants produced more shoot and root growth up to 2 (T2) weeks after transplanting. At 3 (T3) and 4 (T4) weeks after transplanting, there were no differences between 4W, 5W, and 6W transplants. These trends were independent of irrigation systems. Total yield and early yield were similar for all transplant ages. In fall, shoot growth increased linearly with increasing transplant age at TO, but not thereafter. Chlorophyll a + b increased over time, but no treatment differences were found at T4. At planting, 2W transplants had a higher Chl a: b ratio than older transplants. This difference was reduced at T1 and T2 and became insignificant at T4. These results indicate that no improvement in yields was obtained using the traditional older transplants. Younger transplants might be used to achieve rapid seedling establishment with-minimal transplant production costs.

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Daniel I. Leskovar, Daniel J. Cantliffe, and Peter J. Stoffella

`Sunny' tomato (Lycopersicon esculentum Mill.) containerized transplants were grown with the standard or conventional systems (SS) and with recently developed flotation systems (FS). Standard system and FS transplants, and direct-seeding using coated seeds were evaluated in the field for root and shoot growth and yield at Parrish, Bradenton, and Naples during fall, winter, and spring plantings. Plant growth characteristics were measured weekly before, during, and after transplanting or sowing. In the Parrish and Bradenton Fall 1987 and Bradenton Spring 1988 experiments, SS transplants had greater leaf area, root volume, shoot dry weights, and shoot: root ratios than FS transplants. During early development, the FS transplants had more lateral root growth than SS transplants, but had similar total root growth and horizontal and vertical root distribution after transplanting in the field. Transplants and direct-seeded plants allocated 72% of the total root mass in the upper 0 to 10 cm of the soil. In Fall 1987, SS transplants had between 29% and 41% more fruit yield than FS transplants at Bradenton and Parrish, respectively. In the Naples Winter 1988 and Parrish and Bradenton Fall 1989 experiments, both transplant types had similar fruit yields, but more than direct-seeded plants. Transplants grown with the flotation system are recommended for use provided that seedlings are grown and maintained with minimum hardening before establishment in the field.

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Raymond P. Chée, Daniel I. Leskovar, and Daniel J. Cantliffe

Embryogenic callus growth of sweetpotato [Ipomoea batatas (L.) Lam.] was selectively enhanced by subculture on basal callus proliferation medium modified to contain 15 mm NH4NO3. Embryogenic callus production was doubled on basal callus proliferation medium modified to contain 60 mm K+, while nonembryogenic callus production was reduced 40%. Additions of up to 40 mm NaCl to basal callus proliferation medium did not affect callus proliferation. The development of embryos from calli subculture to embryo production basal medium was unaffected by the KCl or NaCl treatments of the callus proliferation phase. However, embryo production was increased by subculturing callus from callus proliferation medium containing 20 mm NH4 + to embryo production medium containing 10 mm NH4 + Our results demonstrate that changes in mineral nutrition, in addition to growth regulator differences between callus proliferation and embryo production media, are important factors in sweetpotato somatic embryogenesis.