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  • Author or Editor: W.V. Welker x
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Oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide), simazine (2-chloro-4,6-bis(ethylamino)-s-triazine), and diuron (3-(3,4-dichlorophenyl)-l,l-dimethylurea) alone and combinations of oryzalin plus simazine or diuron were applied annually for 4 years to young peach (Prunus persica L.) trees. The effectiveness of each herbicide decreased as years of use increased. Weed population shifts occurred with continuous use of the same herbicide. Herbicide combinations resulted in better weed control than did the monoherbicide treatments. Growth and yield were highly correlated with increased weed control.

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Peach [Prunus persica (L.) Batsch] trees were planted in killed sod developed from five different grasses. Tree growth was evaluated within the killed-sod treatments, as well as between killed-sod and bare soil treatments. Canopy width, tree height, and trunk cross-sectional area were all greater in the killed-sod treatments than in the bare soil treatments. All five grasses tested were acceptable for developing a killed-sod mulch. Chemical names used: N-(phosphonomethyl) glycine (glyphosate); N1(3,4-dichlorophenyl)-N,N-dimethylurea (diuron); 5-chloro-3-(1-1-dimethylethyl)-6-methyl-2,4(1H,3H)-pyrimidinedione (terbacil).

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Our objectives in this study were to measure the effects of low levels of root system carbon dioxide on peach tree growth (Prunus persica L. Batsch) and nutrient uptake. Using soil and hydroponic systems, we found that increased root CO2: 1) increased root growth without increasing shoot growth, 2) increased leaf P concentration, 3) decreased leaf N concentration, and 4) reduced water use relative to air injection or no treatment.

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Peach (Prunus persica L. Batsch) trees were grown for five growing seasons in uniform-sized vegetation-free areas arranged in three patterns within a tall fescue (Festuca arundinacea Schreb.) sod. Trees grown in a vegetation-free area arranged in a strip pattern grew better than trees grown either in the center or edge of a square. The distribution pattern of the vegetation-free area influenced growth during the first 4 years; however, at the end of 5 years, differences in canopy width and trunk cross-sectional area were minimal. Thus, there is much latitude in distributing the available vegetation-free area as orchard floor management practices dictate.

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Carbon dioxide is produced by microbial and plant respiration and accumulates in the soil. In previous field studies, CO2 levels were higher under a killed sod soil management system, relative to cultivation and herbicide systems (1.8 vs 0.8 and 1.0%), respectively. Our objective in these studies was to measure the effect of elevated levels of root system CO2 on root and shoot growth and nutrient uptake. Using soil and hydroponic systems in greenhouse studies, we maintained root system CO2 levels between 1.5 and 2.5%. Control CO2 levels were less than 1%. Root length density and dry matter partitioning to the root system were increased by root CO2 in soil and hydroponic studies; shoot growth was unaffected. In hydroponic culture, root CO2 increased P uptake, solution pH, root volume and the number of lateral roots/cm root axis. Elevated levels of CO2 in the root system stimulated root growth in both the soil and hydroponic studies.

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The effect of ground covers on water uptake was studied using peach trees grown in a 4-part split root system. In 1992, one section of the root system was in bare soil and 3 sections were in combination with `K-31' tall fescue. In 1993, K-31 was eliminated in 2 additional sections, leaving 1 section in combination with `K-31'. When grass transpiration was suppressed by covering the K-31, tree water uptake/cm of root length was greater in the presence of grass compared to bare soil under well watered conditions. These data indicate that peach trees compensate for interspecific competition by increasing root hydraulic conductivity.

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We determined how differences in peach tree water use and shoot and root growth due to ground cover treatments are affected by tree response and soil conditions in the adjacent soil environment. Ground cover combinations of bare soil (BS), a killed K-31 tall fescue sod (KS), a living Poa trivialis sod (PT), and a living K-31 tall fescue sod (LS) were imposed on 50% of the soil surface in greenhouse studies. The ground cover on 50% of the soil surface influenced root and top growth of the peach trees [Prunus persica (L) Batsch], water use, and NO3-N levels in the opposing 50%, depending on the competitiveness of the cover crop (LS vs. PT and KS) and characteristics of the soil (BS vs. KS). Tree growth was allometrically related to root growth.

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Planting sod beneath peach trees (Prunus persica) to control excessive vegetative growth was evaluated from 1987 to 1993 in three field studies. Peach trees were established and maintained in 2.5-m-wide vegetation-free strips for 3 years, and then sod was planted beneath the trees and maintained for 5 to 7 years. Reducing the vegetation-free area beneath established peach trees to a 30- or 60-cm-wide herbicide strip with three grass species (Festuca arundinacae, Festuca rubra, Poa trivialis), reduced total pruning weight/tree in 5 of 16 study-years and weight of canopy suckers in 6 of 7 study-years, while increasing light penetration into the canopy. Fruit yield was reduced by planting sod beneath peach trees in 5 of 18 study-years; however, yield efficiency of total fruit and large fruit (kg yield/cm2 trunk area) were not reduced in one study and in only 1 year in the other two studies. Planting sod beneath peach trees increased available soil water content in all years, and yield efficiency based on evapotranspiration (kg yield/cm soil water use plus precipitation) was the same or greater for trees with sod compared to the 2.5-m-wide herbicide strip. Planting sod beneath peach trees has the potential to increase light penetration into the canopy and may be appropriate for high-density peach production systems where small, efficient trees are needed.

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Seedling `Tennessee Natural' peach [Prunus persica (L.) Batsch] trees were grown in a series of five greenhouse experiments to determine how peach root development was affected by the interaction of soil pressure potential and the presence of Kentucky-31 (K-31) tall fescue (Festuca arundinaceae Schreb.). Peach trees were grown in split-root rhizotrons that had four separate root growth sections. When two of the four sections had live sod (LS) and two remained bare soil (BS), there was no effect of the LS on peach root development when the trees were irrigated daily. Peach root development was reduced in BS and LS treatments when soil pressure potential was less than -0.06 MPa. In contrast, when trees were grown in rhizotrons that had all four sections with either LS or a killed K-31 sod (KS), peach root development was reduced in the LS treatment compared to the KS treatments when irrigated daily or when soil pressure potential reached -0.03 MPa. The apparent root surface water potential of peach trees in the LS treatment was -0.4 MPa lower than that in the KS treatment under daily irrigation due to the interference of the K-31 tall fescue. In two additional experiments using peach trees with BS in all four sections, we maintained three sections at field capacity and allowed one section to dry to -0.06 to 1.5 MPa. During the night, when transpiration was low, water was transferred to the dry soil section via the peach root system from the three wet soil sections. It appears that the root system of peach can maintain root development in the presence of tall fescue by transferring water from regions of high water availability to those of low availability.

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The objective was to determine the interrelationship between root growth and plant available soil water (PAW) for young, nonbearing, and mature fruiting peach trees (Prunus persica L. Batsch) over 7 years. Root growth observed with minirhizotrons indicated that young, nonbearing trees developed new white roots throughout the growing season. The pattern of new white root growth became bimodal when the trees fruited. White root production in mature trees appeared in March, preceding budbreak, ceased in June, resumed following fruitremoval in August, and persisted through January. The appearance of white roots was inversely related to the presence of fruit and was not correlated to PAW levels in the 0 to 90 cm depth. The lack of root growth response to PAW levels was attributed to a root system that penetrated the soil to depths beyond our zone of sampling. Circumstantial evidence suggests that deep roots help maintain the surface root system when the surface soil dries.

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