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Potassium has important physiological functions in eucalypt plantations, increasing their productivity when applied to soil via mineral fertilizers. There is interest in identifying alternative sources to KCl owing to its high cost and limited reserves. The aim of the study was to test the effect of replacing KCl with NaCl and phonolite rock powder. Two comparisons were made: (1) application of 283 kg ha−1 of KCl compared with that of 2125 kg ha−1 of phonolite rock powder (equivalent to 170 kg ha−1 of K2O in both treatments); (2) application of 139 kg ha−1 of NaCl compared with that of 183 kg ha−1 of KCl (equivalent to 2.33 kmol Na and K, respectively). Radial growth, soil water content, leaf water potential (Ψ), accumulated transpiration, stem volume and biomass increment, as well as water use efficiency (WUE) were evaluated. In the first comparison, both fertilizations presented equal values for all characteristics evaluated. In the second, the accumulated transpiration in trees fertilized with KCl was 17% higher than that in plants fertilized with NaCl. In contrast, the WUE was 20% higher in the trees fertilized with NaCl than in those fertilized with KCl, reflecting the lower water consumption for the same increment in stem volume and biomass. We conclude that phonolite rock powder and NaCl are possible substitutes for conventional K fertilization performed with KCl. [ABSTRACT FROM AUTHOR]

• The drought resistant clone used as much or more water than the high productivity clone across dry, mesic and wet sites. • Water use efficiency for the drought resistant clone was lower than the high productivity clone at the dry and mesic sites. • The drought resistant clone may allocate more resources to roots leading to increased water use. • Decisions to plant drought resistant clones on arid or marginal lands may have unexpected impacts on water resources. Eucalyptus plantation productivity has increased 4-fold across Brazil as a result of improved genetic selection and intensive silviculture. However, the rate of productivity improvements is slowing and suggests increased production will require planting in areas that have never been previously planted with Eucalyptus with uncertain impacts on local water supplies. This study compares water use and water use efficiency between a drought resistant (E. grandis × E. camaldulensis) and high productivity Eucalyptus clone (E. urophylla) across three sites (dry, mesic and wet) spanning a two-fold precipitation gradient (~600–1350 mm y−1) in Brazil. Each site included a 30% reduced rainfall treatment for each clone to investigate within site response to reduced precipitation. We found that the drought resistant clone used as much or more water than the high productivity clone at all three sites. The drought resistant clone transpired almost 20% percent more water than the high productivity clone at the dry site (3.7 vs. 3.0 m3 y−1) while water use between clones did not differ at the mesic (4.6 vs 4.0 m3 y−1) and wet site (4.0 vs 4.5 m3 y−1). The high productivity clone transpired 54, 46 and 37% of annual precipitation at the dry, mesic and wet sites respectively while the drought resistant clone consumed 67, 47 and 31% of annual precipitation from the dry to the wet site. Although the rain reduction treatments did not impact annual water use for either clone at the dry and mesic sites, there were some differences at a subannual timescale. Rain reduction treatments at the dry site lowered transpiration in the driest, hottest three months for the high productivity clone by 25–32%. Rainfall reduction led to lower water use by the drought resistant clone for only one month during the dry season (18%). The high productivity clone transpired less water (24–26%) in the rainfall reduction treatment at the mesic site during three months and the drought resistant clone transpired 18 and 20% less water in the rainfall reduction treatment during two months. Rainfall reduction reduced annual transpiration by 59% for the high productivity clone at the wet site. Average water use efficiency of the drought resistant clone was almost 70% lower than the high productivity clone at the dry and mesic sites (~5.2 vs. 1.5 kg m−3 y−1) and was due to the combination of low growth and high water use. Higher than expected growth by the drought resistant clone at the wet site resulted in similar water use efficiency between clones (6.3 vs. 5.8 kg m−3 y−1). We discuss potential implications of our findings and highlight several lines of evidence that suggest the drought resistant clone in this study allocates a greater proportion of gross primary productivity below ground allowing it to access deeper reserves of soil water during dry periods. Our results suggest that decisions to plant drought resistant clones in drought prone areas should be carefully considered and also highlight the need for more research on water use and drought tolerance strategies for Eucalyptus clones bred for more arid areas in Brazil. [ABSTRACT FROM AUTHOR]

• Leaf area index (LAI) varied among clones but increased with planting density. • Average stand transpiration at low tree density was 40% lower (622 mm) than that exhibited by high density (879 mm). • Selection of clonal material and silvicultural treatments could maximize productivity while minimizing water use. • WUE were significant different among three clones, but it was not sensitive to planting density variation. We examined the influence of stand density and genotype on transpiration and water use efficiency in high productivity plantations. Three widely planted Eucalyptus clones that differ in drought tolerance and productivity (E. urophylla , E. urophylla × E. grandis and E. grandis × E. camaldulensis, clones IP, B2 and C3, respectively) were measured at four densities (590, 1030, 1420, and 2950 trees ha−1). Over the 1-year study period (1.5–2.5 years after planting), individual biomass increment decreased with increasing density, from 21 kg tree−1 at 590 trees ha−1 to 6 kg tree−1 at 2950 trees ha−1. Stand increment typically follows the reverse pattern, increasing as density increases. This was the case for two clones (IP and B2), but stand increment was consistent across tree spacings for C3. Transpiration increased with density, from a low of 622 mm yr−1 to a high of 879 mm y−1. Some of the increased water use resulted from higher leaf area index at higher densities. The B2 clone transpired the most water on average, produced the greatest increment (23 Mg ha−1 yr−1 for 1030 trees ha−1), and produced the most wood L−1 transpiration (water use efficiency, 2.3 g biomass L−1). The clone C3 had the lowest increment (only 12 Mg ha−1 yr−1) because of the combination of low transpiration and low water use efficiency (only 1.5 g biomass L−1). Optimizing clone selection and silviculture for the combination of high yield and high water use efficiency may help reduce risks from drought as well as water conservation. [ABSTRACT FROM AUTHOR]