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• W218284138 abstract "'Valencia' orange tree trunk and canopy growth, leaf nitrogen level, water potential, fruit yield, and fruit quality were decreased by competition from annual weeds and bermudagrass. Soil moisture levels were lower where weeds were present. The adverse effects of the weeds on the trees were related to the intensity of weed competition. Control of annual weeds and bermudagrass reduced the adverse effects of the trees in propor­ tion to the amoun~ of weed control. Many of documented effects of weeds on citrus have been reviewed previously by Jordan.3 ,4 It it widely believed that weeds compete with trees for water and nutrients. The extent of the competition varies with each orchard. The result of the com­ petition is reduced tree growth and fruit yield. The reasons for the reduction have not often been documented. More published data is needed concerning effects of weeds on tree growth and physiology and on fruit quality and yield. Materials and Methods Research was performed to determine the effects of different weed populations, weed control, and itrigation methods on soil moisture and growth, leaf water, nitrogen and chlorophyll, fruit quality and yield of 'Valencia' orange trees. Trees planted in 1965 were maintained 12 years under furrow irrigation; the orchard was kept weed-free with annual soil treatments using simazine [2-cWoro-4,6-bis(ethylamino)-s-triazine] and postemergence ap­ plications of weed oil to weeds which had escaped simazine treatment. After 1976, one-half of the orchard was sprinkler irrigated and the other half was furrow irrigated. Each irrigated section was divided into blocks with two rows of nine trees. To establish weedy plots, herbicide treatments were dis­ continued. The soil was rotary-tilled to 5-cm depth to prepare the seed bed, dilute simazine in the soil, and move annual weed seeds to the soil surface for germination. Naturally occurring annual broadleaf weeds, such as redroot pigweek (Amtlranthus retro­ flexus L.), horseweed [Conyza canadensis (L.) Crong.], bullthistle [Orsium vulgare (Savi) Tenore], pale smartweed (Polygonum lapathifolium L.), mixed annual grasses (Bromus L. and Hordeum L. sp.) and other species were allowed to germinate and grow. Bermudagrass, (Cynodon dactylon (L.) Pers.) cv. Tifway stolons were incorporated into the top 2 cm of soil. Ammonium nitrate at the rate of 121 kg N/ha was applied annually in each March. Annual and bermudagrass weed vegeta­ tion were allowed to become established for two years on.all plots except those plots where no weeds were allowed to grow. Plots were then established in which weeds were completely controlled, partially controlled (avg. 50%), or left uncontrolled. To achieve partial control, paraquat treatments (0.5 kg/ha) were begun in Spring 1979 to selected plots containing either mixtures of annual weeds or bermudagrass. Neither annual weeds nor bermudagrass were eradicated but regrew after each treat­ ment. Bermudagrass was resprayed when regrowth reached about 50%; annual weeds were resprayed before regrowth was about 30 cm tall and covered 50% of the plot surface. Annual weeds were suppressed with 5 paraquat treatments, while bermudagrass required 7 treatmen ts at 0.6 kg/ha in 468 I/ha of water. Complete weed control was achieved during the experiment with simazine in the undisturbed soil, by the lack of viable weed seed in the surface soil, and by removal of the few seedlings that emerged. Annual weeds and bermudagrass covered more than 95% of the ) soil surface of plots where no weed control was practiced. Tree, leaf, and fruit parameters were determined in six ; replicated single tree plots in blocks which were surrounded by border trees. There were three blocks of bermudagrass under sprinkler irrigation and three blocks of annual weeds under either furrow or sprinkler irrigation. Soil moisture was measured at two-week intervals at 23, 46, and 92 cm depths midway between the trees in line with the trunks with a neutron moisture probe.6 Tree size was measured each October by determining the' trunk circumference 10 cm above the bud union and by calculating the tree volume from the width and height of the tree canopy. The winter growth flush was evaluated by counting the number and length of new shoots: formed on each tree during December. The total leaf area per tree; was calcula.ted by determining the number of leaves per tree and i leaf area. Tree water status was determined by measuring the leaf i water potential with a pressure chamberS two hours before sunrise (predawn) and at 1100 through 1300 hr (midday). Photosynthesis was measured with a double isotope poro­ meter. 2, 7 Measurements were made at mon thly intervals through­ out the year on leaves one meter abuvr. the soil surface with uniform maturity, size, and illumination on the south side of the trees. Nitrogen content was determined for leaves on six-month­ old, non-fruiting terminals from spring cycle growth by the micro-kjeldaW method. l CWorophyll content of leaves was determined montWy with a portable reflectance meter. 8 At 'I harvest, 18 fruit were picked at random from each tree for quality determinations. Results and Discussion Soil moisture. Increased control of either annual weeds or bermudagrass generally increased soil moisture at 23, 46, and 92 cm deep (Table 1). In either sprinkler or furrow irrigation, soil I moisture was greatest with complete weed control and least : where there was no weed control; the only exception to this was ,i Table 1. Average soil moisture (1981) at three depths in a 'Valencia-' I, orange orchard grown with different methods of irrigation and weed vegetation, and three levels of weed control. Irrigation Vegetation Control Depth (cm)" @default.
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• W218284138 date "1983-01-01" @default.
• W218284138 modified "2023-09-26" @default.
• W218284138 title "Weeds affect citrus growth, physiology, yield, fruit quality." @default.
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