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  • Author or Editor: Josiah W. Worthington x
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Budded, bare root, `Wichita' pecan trees were planted and grown in inexpensive, 2m X.75m, non-weighing lysimeters for three growing seasons. Metered water was applied automatically through microirrigation systems as called for by switching tensiometers. Soil moisture tension was not allowed to exceed 25 Kpa. All tree/sod combinations received 336 kg N per hectare from 1-1-1 ratio commercial fertilizer.

Water use, tree growth, and nutrient status of trees grown under the following orchard floor management practices were measured: 1)Unmowed coastal bermudagrass. 2)Mechanically mowed bermudagrass, 3)Chemically mowed bermudagrass, and 4)Bare soil.

Water use by trees with chemical or mechanically mowed sod were intermediate in water use between unmowed and fallow soil treatments. In spite of the fact that water was never limiting for any treatment, fallow trees grew significantly larger than trees in any of the sodded treatments. A significantly lower level of foliar potassium was noted in trees growing in sod systems.

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Contrasting colors of plastic mulch (black and white over black) were used to modify the rate at which heat units (HU) were accumulated in four different microclimates surrounding watermelon plants during 1996 at the Texas Agricultural Experiment Station-Stephenville. Daily maximum and minimum temperatures from 25 Mar. through 4 Aug. were recorded for air 10 cm above the mulch surface, at the mulch surface, at the soil surface under mulch, and 10 cm below the soil surface under mulch. Accumulated HU were significantly higher for white than for black mulch during two of the four periods monitored; however, the reverse was true for all other points of measurements at all times. Daily mean soil surface heat gain was 3.29 HU higher under black than under white mulch in early season, 6.21 higher in late April and early May, 5.19 higher in late May and June, and 4.19 higher in late June through July. Values for soil at 10-cm depth paralleled those for soil surface.

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Field studies were conducted June 2, July 27, and October 15, 1988 to determine root concentrations within the dry and wetted soil of trickle-irrigated peach trees (Redglobe variety) in Windthorst fine sandy loam soil. Two “dryland” and four irrigation treatments (based on time of year irrigation initiated and previous irrigation history) were used. A single soil core sample 2.2 cm in diameter and 80 cm deep was taken 50 cm from trickle emitters on each of 8 trees per irrigation treatment and a single sample taken the same distance from the trunk on the “dry” side of the 8 trees in each dryland treatment. Each core was sectioned into 20-cm increments, washed, roots collected, separated (small, feeder roots; large suberized roots), dried and weighed.

Analyses of data for the small, feeder roots showed a significant difference (0.01 level) in root density between treatments, between sample times (each treatment), and with depth (each treatment). Root concentrations were highest in soils that had received irrigation in previous years and also when irrigation was initiated early in the year. Root concentrations were also found to be highest in the top 20 cm of soil regardless of treatment.

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Field studies were conducted June 2, July 27, and October 15, 1988 to determine root concentrations within the dry and wetted soil of trickle-irrigated peach trees (Redglobe variety) in Windthorst fine sandy loam soil. Two “dryland” and four irrigation treatments (based on time of year irrigation initiated and previous irrigation history) were used. A single soil core sample 2.2 cm in diameter and 80 cm deep was taken 50 cm from trickle emitters on each of 8 trees per irrigation treatment and a single sample taken the same distance from the trunk on the “dry” side of the 8 trees in each dryland treatment. Each core was sectioned into 20-cm increments, washed, roots collected, separated (small, feeder roots; large suberized roots), dried and weighed.

Analyses of data for the small, feeder roots showed a significant difference (0.01 level) in root density between treatments, between sample times (each treatment), and with depth (each treatment). Root concentrations were highest in soils that had received irrigation in previous years and also when irrigation was initiated early in the year. Root concentrations were also found to be highest in the top 20 cm of soil regardless of treatment.

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Abstract

Evapotranspiration of two 5-year-old mature trees of peach [Prunus persica (L.) Batsch] was measured in weighing lysimeters. Diurnal water use patterns were conventional. Trees used an average of 136, 114, 96, and 61 liters per day in July, August, September, and October respectively, with an overall daily average of 102 liters. The crop coefficient based on class A pan evaporation declined from 0.98 in early July to 0.40 just before leaf fall and averaged 0.71 for the season. Class A pan evaporation correlated well with evapotranspiration on a weekly average but poorly on a daily basis.

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A computer model was used to predict irrigation rates and numbers of emitters or microsprayers required to trickle irrigate Redskin/Nemaguard peach trees. Irrigation rates were 0, 50%, and 100% of the predicted requirement based on a crop coefficient of 50, 80, 100, 80, and 50 percent of pan evaporation for the tree's canopy area for May, June, July, August and Sept. respectively. Full irrigation (100% of predicted) was applied through 6, 8L/hr emitters or one 48L/hr microsprayer. Half the predicted rate was applied through 6, 4L/hr emitters or 1 24L/hr microsprayer. Control trees received no supplemental irrigation. Microsprayers height was adjusted to wet a surface area comparable to the 6 emitters. There was no significant difference in fruit size or yield based on emitter vs microsprayers, but fruit size and total yield was increased in direct proportion to irrigation rate. There was no treatment effect on tree pruning weights. Moisture measurements indicated that trees de-watered the soil efficiently enough that water never moved below the 30 cm level in spite of the fact that up to 260 liters per tree per day were applied in mid-summer.

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The potential for reducing water use of peach [Prunus persica (L.) Batsch] trees with antitranspirants following fruit harvest was investigated using matched peach trees planted in an outdoor twin weighing lysimeter facility. A 10% solution of the antitranspirant Wilt Pruf NCF was applied to one of the two trees on 7 July 1986. Immediately after application, water use of the treated tree was reduced by 40%. One month after treatment, the water use was reduced 30% and, by the termination of the experiment (85 days after treatment), water use was reduced 12% as compared to control. The average reduction in tree water use for the entire period was 30%. Fully expanded, sunlit leaves (nodes 10 to 20 from the terminal end) from the treated tree exhibited the greatest reduction in water loss compared with immature or inner canopy, shaded leaves. Use of the antitranspirant did not prevent the development of water stress once a critical level of soil moisture was reached. The change in tree water use induced by the antitranspirant did not significantly reduce shoot length, new leaf production, or individual leaf size on actively growing, current-season branches. Fruit and leaf bud initiation, as measured the following spring, were not affected: however. flower bud maturation could not be evaluated due to freeze damage. Chemical name used: di-1-p-menthene (Wilt Pruf NCF).

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