Annual course of matric potential in differently used savanna oxisols in Brazil

Sustainable land use in periodically dry Brazilian savannas requires a wate r-saving management. We hypothesized that the annual course of matric poten tials (psi(M)) in very-fine, isohyperthermic Anionic Acrus-toxes of Pinus p lantations (PI), degraded (DP) and productive pastures (PP), no-till (NT) a nd conventional tillage (CT) cropping, and natural savanna (Cerrado, CE) di ffered significantly. On three plots in each of these land-use systems wate r input and psi(M) at the 0.15-, 0.30-, 0.80-, 1.2-, and 2.0-m depths was m easured with tensiometers weekly between 27 Mar. 1997 and 28 Apr. 1998. Pre cipitation between 29 Apr. 1997 and 28 Apr. 1998 was 1562 mm, with only 210 mm in May to September, when psi(M) at the 0.15- and 0.30-m depths decreas ed to less than -80 kPa in all systems; the lowest psi(M) at 2-m depth was -57 kPa. During the monitored period, the PI soils had lower average psi(M) at the 0.8- to 2-m depths (-60 kPa) than those in CE (-46), indicating hig her rainfall interception losses and higher transpiration. In CT, average p si(M) values at the 0.8- to 2-m depths (-29) were higher than in NT (-51) b ecause of different crops and different soil management. Between June and N ovember, psi(M) at the 2-m depth in CE decreased to a lower value (-42) tha n in vegetation-free CT (-22) and NT (-27). In DP and PP soils, psi(M)S wer e similar to those in CE soils at all depths. The estimated average water s torage in the upper 2 m during the monitored period was: 565 mm (CT) > 553 (PP) > 541 (DP) > 537 (CE) > 526 (NT) > 479 (PI). Our results show that mai nly the vegetation type and tillage practices control the annual course of matric potential in differently used savanna Oxisols.