Simulating the effects of different potassium and water supply regimes on soil water content and water table depth over a rotation of a tropical Eucalyptus grandis plantation

Abstract

Although large amounts of potassium (K) are applied in tropical crops and planted forests, little is known about the interaction between K nutrition and water supply regimes on water resources in tropical regions. This interaction is a major issue because climate change is expected to increase the length of drought periods in many tropical regions and soil water availability in deep soil layers is likely to have a major influence on tree growth during dry periods in tropical planted forests. A process-based model (MAESPA) was parameterized in a throughfall exclusion experiment in Brazil to gain insight into the combined effects of K deficiency and rainfall reduction (37% throughfall exclusion) on the water used by the trees, soil water storage and water table fluctuations over the first 4.5 years after planting Eucalyptus grandis trees. A comparison of canopy transpiration in each plot with the values predicted for the same soil with the water content maintained at field capacity, made it possible to calculate a soil-driven tree water stress index for each treatment. Compared to K-fertilized trees with undisturbed rainfall (+K+W), canopy transpiration was 40% lower for K deficiency (−K+W), 20% lower for W deficit (+K−W) and 36% lower for combined K deficiency and W deficit (−K−W) on average. Water was withdrawn in deeper soil layers for −W than for +W, particularly over dry seasons. Under contrasted K availability, water withdrawal was more superficial for −K than for +K. Mean soil water content down to 18 m below surface (mbs) was 24% higher for −K+W than for +K+W from 2 years after planting (after canopy closure), while it was 24% lower for +K−W and 12% lower for −K−W than for +K+W. The soil-driven tree water stress index was 166% higher over the first 4.5 years after planting for −W than for +W, 76% lower for −K than for +K, and 14% lower for −K−W than for +K+W. Over the study period, deep seepage was higher by 371 mm yr −1 (+122%) for −K than for +K and lower by 200 mm yr −1 (−66%) for −W than for +W. Deep seepage was lower by 44% for −K−W than for +K+W. At the end of the study period, the model predicted a higher water table for −K (10 mbs for −K+W and 16 mbs for −K−W) than for +K (16 mbs for +K+W and 18 mbs for +K−W). Our study suggests that flexible fertilization regimes could contribute to adjusting the local trade-off between wood production and demand for soil water resources in planted forests.

Tamm Review: Deep fine roots in forest ecosystems: Why dig deeper?

“…In another Eucalyptus grandis stand, Germon et al 2019showed a negative correlation between the amount of extractable water in the topsoil and the flushes of fine root growth in very deep soil layers. In those plantations, fine root growth in deep soil layers seems to be related to the overall water demand of the whole tree and controlled by the need to use increasingly deeper water resources when water becomes scarce in the topsoil, which is consistent with modeling studies (Christina et al, 2017(Christina et al, , 2018. Vertical growth rates of trees were almost symmetrical above-and below-ground in Eucalyptus plantations, reaching 10.4 and 19.2 m in height and a maximum rooting depth of 9.2 and 15.8 m at 1.5 and 3.5 years after planting, respectively (Christina et al, 2011).…”

A systems biology view of wood formation in Eucalyptus grandis trees submitted to different potassium and water regimes

“…This finding is consistent with previous physiological studies showing that at the end of the dry season, K‐fertilized trees reached a higher level of water stress than K‐deficient trees (Battie‐Laclau et al ., ,b, ). This drought‐induced effect of K‐fertilization was linked to the enhancement of tree growth rate causing a faster decrease in soil water stocks during dry periods (Christina et al ., ). This was particularly true in our study because of the exceptionally low amount of rainfall during the months preceding sampling (Fig.…”

How Does Water-Stressed Corn Respond to Potassium Nutrition? A Shoot-Root Scale Approach Study under Controlled Conditions

“…Water use efficiency results did not show any advantage in applying more K than strictly needed for growth needs, but, as previously mentioned, the experimental bias linked to the delay in plant development did not allow us to form a conclusion. Hence, although K nutrition did partially compensate for water shortage in terms of leaf area and biomass, this may represent a real risk in terms of water mass balance whenever irrigation is not sufficient [65]. Our overall findings suggest that there was no significant advantage to over-fertilizing water-stressed plants with K. The highest level of K fertilization applied to the water-stressed plants did not allow the main plant growth components (green leaf area, leaf lifespan, root biomass, and shoot biomass) to be as high as the well-watered plants fertilized with a non-excessive quantity of K. From a practical point of view, we recommend that farmers should identify their soil-limiting parameters by obtaining soil analysis, and by adapting mineral inputs to the irrigation water facilities.…”