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Daniel I. Leskovar and Giovanni Piccinni

Restrictions placed on water usage for farmers have prompted the development of irrigation management projects aiming at water savings of economically important crops. The objective of this work was to determine yield, water use efficiency, and leaf quality responses to deficit irrigation rates of processing spinach (Spinacea oleracea L.) cultivars. Three irrigation treatments were imposed with a center pivot system, 100%, 75%, and 50% crop evapotranspiration rates (ETc). Commercial cultivars used were `DMC 09', `ASR 157', and `ACX 3665'. Leaf quality was significantly affected by deficit irrigation rate and cultivar. Leaf yellowness was highest at 50% ETc, and was more evident for `ACX 3665'. The percent excess stem (>10 cm) was higher at 100% ETc. This response was greater in `ACX 3665' than in `ASR 157' and `DMC 09'. Marketable yields were significantly higher for `ASR 157' at either 100% or 75% ETc rates, compared to `DMC 09' and `ACX 3665'. High water use efficiency was also measured at 75% ETc for `ASR 157'. Minimum canopy temperature differences were detected among the irrigation treatments. This work demonstrated that it is possible to reach a 25% water savings in one season, without reducing yields when using vigorous cultivars.

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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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Giovanni Piccinni, Jonghan Ko, Thomas Marek and Daniel I. Leskovar

Weighing lysimeters are used to measure crop water use during the growing season. By relating the water use of a specific crop to a well-watered reference crop such as grass, crop coefficients (KC) can be developed to assist in predicting crop needs using meteorological data available from weather stations. This research was conducted to determine growth stage-specific KC and crop water use for onions (Allium cepa L.) and spinach (Spinacia oleracea L.) grown under south Texas conditions. Seven lysimeters, consisting of undisturbed 1.5 × 2.0 × 2.2-m deep soil monoliths, comprise the Texas AgriLife Research–Uvalde lysimeter facility. Six lysimeters, weighing ≈14 Mg, have been placed each in the middle of a 1-ha field beneath a linear low-energy precision application irrigation system. A seventh lysimeter was established to measure reference grass reference evapotranspiration. Daily water use for onion and spinach was measured at 5-min intervals. Crop water requirements, KC determination, and comparison with existing Food and Agricultural Organization (FAO) KC values were determined over a 2-year period for each crop. The KC values determined over the growing seasons varied from 0.2 to 1.3 for onion and 0.2 to 1.5 for spinach with some of the values in agreement with those from FAO. It is assumed that the application of growth stage-specific KC will assist in irrigation management and provide precise water applications for a region of interest.

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Daniel I. Leskovar*, Darrin J. Moore, Libbie Johnson, Julio Loaiza and Giovanni Piccinni

Regulations restricting water use, competition for water with large urban sector, coupled with extreme high temperatures have placed a large strain on farming areas in south Texas. In addition, consumer demand for healthy vegetables has increased. The objective of this work was to determine yield and fruit quality to deficit irrigation rates and irrigation systems on poblano pepper cv. Tiburon. In 2002, an experiment was conducted at the TAES-Uvalde with a Center pivot using three irrigation rates, 100%, 80%, and 60% evapotranspiration rates (ETc). Transplants were established on beds 1.0 m apart with plants within rows 45 cm apart. In 2003, we compared production efficiency of four irrigation systems in a urban-rural environment near San Antonio. Beds were 0.9 m (single-row) or 1.8 m (double-row) between centers. Irrigation systems were: 1) furrow irrigation with one line/single beds, 2) subsurface drip (SDI)-no mulch, with one line/single bed, 3) SDI-no mulch, with two lines/double bed, and 4) SDI-white mulch with two lines/double bed. In 2002, summer ratooning of the spring-planted crop under deficit irrigation (<100% ETc) allowed a fall crop with a 2.0 fold yield increase, larger fruit size (greater than 10 cm length) and significantly lower defects caused by sunburn or blossom end rot compared to summer production. In 2003, SDI-white mulch had a 2.4-fold yield increase and 760 mm water savings compared to furrow. Fruit vitamin C content was not affected by irrigation, however, mature red fruits had a 3.6 fold increase compared to mature green fruits. Combining deficit irrigation with ratooning we were able to produce marketable poblano fruits. Additional water savings and increased yield were demonstrated by SDI technology.

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Daniel Leskovar, Smiljana Goreta, Kil Sun Yoo, Giovanni Piccinni and Shinsuke Agehara

Introduction of artichokes in the Wintergarden of Texas, an area with mild winters and hot summers, depends on the development of strategies that will overcome limiting climatic conditions for bolting, earliness, and length of harvest. Cultivars with different bolting requirements were evaluated at two planting times and irrigation rates. The cultivars Emerald, Experimental Red, Imperial Star, Green Globe, and Purple Romagnia were transplanted in the field on 27 Sept. and 3 Dec. 2004, and evaluated at 100% and 75% crop evapotranspiration rates (ETc) at Uvalde, Texas (29°1' N; 99°5' W). Harvests started on 24 Mar. and 21 Apr. 2005 for the first and second planting dates, respectively. Yield increased more than 3-fold for the first compared to the second planting date. Irrigation rates did not affect yield, water use efficiency, or head quality. The cultivars Emerald, Imperial Star, and Experimental Red were earlier than Green Globe and Purple Romagnia. The highest yield was measured for cv. Imperial Star, while the largest head weight was for cv. Green Globe. Total fibers, crude protein, and phenolic compounds concentration depended on cultivar, whereas the total sugar concentrations in the edible part of the head were similar among cultivars. Head weight, percentage of heart, and crude protein concentration decreased, whereas total fiber content increased as the harvesting season progressed. Integrating environmental and cultivar strategies aimed at earliness, large head size, and enhanced level of health-promoting compounds, will contribute to the potential production of globe artichokes in the region.

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Giovanni Piccinni, Thomas Gerik, Evelyn Steglich, Daniel Leskovar, Jonghan Ko, Thomas Marek and Terry Howell

Improving irrigation water management for crop production is becoming increasingly important in South Texas as the water supplies shrink and competition with urban centers in the region grows. Crop simulators and crop evapotranspiration (ET) are appealing methods for estimating crop water use and irrigation requirements because of the low investment in time and dollars required by on-site (in-field) measurement of soil and/or crop water status. We compared the effectiveness of the Crop.m.an/EPIC crop simulator and Crop-ET approaches estimating the crop water use for irrigation scheduling of spinach. In-ground weighing lysimeters were used to measure real-time spinach water use during the growing season. We related the water use of the spinach crop to a well-watered reference grass crop to determine crop coefficients (Kc) to assist in predicting accurate crop needs using available meteorological data. In addition, we ran several simulations of CropMan to evaluate the best management for growing spinach under limited water availability. Results show the possibility of saving about 61 to 74 million m3 of water per year in the 36,500 ha of irrigated farms of the Edwards aquifer region if proper irrigation management techniques are implemented in conjunction with the newly developed decision support systems. We discuss the implications of the use of these technologies for improving the effectiveness of irrigation and for reducing irrigation water requirements in South Texas.