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Florida citrus trees must be irrigated to reach maximum production due to low soil water-holding capacity. In a highly urbanizing state with limited water resources, improved understanding of soil water uptake dynamics is needed to optimize irrigation volume and timing. The objectives of this study were: (i) estimate mature citrus daily evapotranspiration (ETc) from changes in soil water content (θ), (ii) calculate citrus crop coefficients (Kc) from ETc and reference evapotranspiration (ETo), (iii) determine the relationship of soil water stress coefficient (Ks) to θ, and (iv) evaluate how ETc was related to root length density. In a 25-mo field study using mature `Hamlin' orange [Citrus sinensis (L.) Osbeck] trees, ETc averaged 1137 mm yr-1, and estimated Kc ranged between 0.7 and 1.1. Day of year explained more than 88% of the variation in Kc when θ was near field capacity. The value of Ks decreased steadily from 1.0 at field capacity (θ = 0.072 cm³ cm-3) to approximately 0.5 at 50% available soil water depletion (θ = 0.045 cm³ cm-3). Roots were concentrated in the top 15 cm of soil under the tree canopy (0.71 to 1.16 cm roots cm-3 soil), where maximum soil water uptake was about 1.3 mm³ mm roor-1 d-1 at field capacity, decreasing quadratically as θ decreased. Estimating daily plant water uptake and resulting soil water depletion based on root length density distribution would provide a reasonable basis for a citrus soil water balance model. [ABSTRACT FROM AUTHOR]

We try to elucidate which environmental and soil factors control nitrogen uptake efficiency in citrus. Effects of residence time and nitrogen (N) concentration (three 500‐mL applications of 7 mg N L−1, representative of reclaimed water used for citrus irrigation in central Florida, or one 150‐mL application of 70 mg N L−1) on nitrogen uptake efficiency (NUE) of young citrus seedlings were studied. Increasing residence times from 2 to 8 h increased NUE from 36 to 82% and from 17 to 34% for high and low application frequencies, respectively. We developed a model to predict N uptake based on root density, N concentration, and soil temperature (Ts). Assuming a base temperature (Tb) of 10°C, N uptake temperature sum (UTS) = ∑(Ts − Tb)/24 (°CdN, degree day units of N uptake). To eliminate the risk of N leaching for young seedlings, minimum uptake periods of 5 and 16°CdN were required at initial soil N concentrations of 0.9 and 2.5 mg N L−1, respectively. After correcting for differences in root length, this information was then used to predict the effect of irrigation practices on N uptake from reclaimed water for mature trees. Applying 2500 mm yr−1 vs. 400 mm yr−1 reclaimed water reduced the NUE of N in this water from 100 to 63% during the summer and from 100 to 28% during the winter. Reductions in NUE at higher irrigation rates appeared to be related to N displacement below the root zone prior to complete N uptake. [ABSTRACT FROM AUTHOR]

Highlights: [•] Studies on three soil types to determine the effect of harvest method on microclimate. [•] Soil temperature increases at burning were in order of sand soils>clay>muck. [•] Temperature increases dissipated much faster in clay soil than muck soil. [•] Burning may have minimal impact on soil microflora and fauna at the studied depths. [•] Crop canopy damage by frost is more likely to occur with green cane harvest. [Copyright &y& Elsevier]

Florida citrus groves are typically grown in two regions of the state: flatwoods and ridge. The southern flatwoods citrus area has poorly drained fine textured sands with low organic matter in the shallow root zone. Ridge citrus is located in the northern ridge citrus zone and has fine to coarse textured sands with low water-holding capacity. Two commercial citrus groves, selected from each region, were studied from 15 July 2004 to 14 July 2005. The flatwoods citrus (FC) grove had a grass cover and used drainage ditches to remove excess water from the root zone. The ridge citrus (RC) grove had a bare soil surface with weeds periodically eliminated by tillage. Citrus crop evapotranspiration (ETc) rates at the two citrus groves were measured by the eddy correlation method, and components in the energy balance were also examined and compared. The study period had higher than average rainfall, and as a result, the two locations had similar annual ETc rates (1069 and 1044 mm for RC and FC, respectively). The ETc rates were 59% (RC) and 47% (FC) of the rainfall amounts during the study period. The annual reference crop evapotranspiration (ETo) rates were 1180 ram for RC and 1419 ram for FC, estimated using the standardized reference evapotranspiration equation. The citrus crop coefficients (Kc, ratio of ETc to ETo) were different between the two locations because of differences in latitude, ground cover, and rainfall amounts. The Kc values ranged from 0. 70 between December and March to 1.05 between July and November for RC, and from 0.65 between November and May to 0.85 between June and October for FC. The results are consistent with other Kc values reported from field studies on citrus in both Florida and elsewhere using these and alternate methods. [ABSTRACT FROM AUTHOR]