Water availability limits early growth of poplar (Populus spp.) in the Plane Pampas of Central Argentina

ACHINELLI, FABIO; ANGELINETTI, SEBASTIÁN; DELGADO, MAXIMIANO; SKORUPSKI, EDUARDO; LUQUEZ VIRGINIA M.C.

Beijing, China

Conferencia; 23rd session of the International Poplar Commission (IPC): Poplars, willows and people´s wellbeing; 2008

FAO (Food and Agriculture Organization od the United Nations), Beijing Forest University, State Forestry Administration, Chinese Academy of Forestry

Water availability limits early growth of poplar (Populus spp.) in the Plane Pampa of Central Argentina. Fabio G. Achinelli123, Sebastian P. Angelinetti1, Maximiano R. Delgado1, Eduardo Skorupski4, Virginia M.C. Luquez2. 1 – Cátedra de Silvicultura, Facultad de Ciencias Agrarias y Forestales UNLP, CC 31 (1900) La Plata, Buenos Aires, Argentina. fachinel@agro.unlp.edu.ar. 2 – INFIVE, CONICET (CCT La Plata) - UNLP, CC 327 (1900) La Plata, Buenos Aires, Argentina. 3- CIC, Buenos Aires, Argentina. 4- Papel Prensa SAICF y M, E. “El Gazapo”, San Gregorio, Santa Fe, Argentina. In Argentina, most poplar (Populus spp.) plantations are located at Paraná River Delta, an area where episodes of flooding frequently lead to disruptions in wood supply. This fact prompted the development of poplar plantations in agricultural soils at the humid pampas in central Argentina (33° to 36° S Lat., 57° to 63° W Long.). In this area, annual rainfall ranges between 700 to 1000 mm, and the distribution of the rainfall during the growing season may be uneven. In particular, the occurrence of dry periods in summer, when lack of rainfall is combined with high evaporative demand, could be limiting growth, since commercial plantations are not irrigated. It has been shown that there is variation in water stress tolerance between P.  deltoides Marsh. and P. x canadensis Mönch clones, but a systematic evaluation of drought tolerance in clones planted in Argentina has not been carried out. The aim of this work was to determine which clones are most sensitive to naturally occurring drought episodes during the growing season. A field experiment was carried out at El Gazapo site (34º 12´ S Lat.; 61º 43´ W Long.; 90 m elev.) where nine clones were planted in August 2007 on a typical hapludoll. The experiment design was a split-plot, with 54-plant main plots replicated in tree randomized complete blocks. Main plots were set with and without irrigation, and clones were laid in 6-plant subplots. The irrigation treatments were applied from November 2007 to April 2008 and consisted of: 1- plants received only natural rainfall (515 mm in total), 2 – plants were watered weekly with an equivalent of 36 mm of rainfall when natural precipitation didn´t reach a minimum of 45 mm in the previous week. Measurements were taken in 4 dates: November 15, December 13, 2007, and February 11, April 20, 2008. In the last date, all clones had set the terminal bud. The variables measured were: basal diameter (mm), total height (m), individual leaf area of the last expanded leaf (ILA, cm2) and leaf area (LA, cm2) of leaves formed during each period of sampling. Clonal responses to irrigation were significantly different. The ILA and the LA produced between measurements were higher in the irrigated plants, but there were differences in the clones as well, with significant clone x irrigation interactions. Cumulated growth at the end of the season expressed as volume index (VI, dm3 = [(basal diameter)2] · total height), was always lower in the non-irrigated treatment, but the intensity of response varied between clones. To quantify drought susceptibility, we calculated growth increases due to irrigation, by taking non irrigated plots as reference growth levels. The extreme responses were found in P. deltoides Catfish 2 clone which grew 11.3 times more in watered plots than in the non-irrigated treatment, while in clone P. x canadensis `Guardi´ this increment was only 3.5 times. Using VI data, we made a ranking of clone responses to drought, taking Catfish 2 as the most sensitive and Guardi as the less sensitive, being the others in intermediate positions. This work shows that water availability can limit productivity in poplar plantations of Argentinean plane Pampa, and that some poplar genotypes perform better than others under this adverse condition. Key words: Populus spp., plane pampas, early growth, water availability, volume index, Argentina.