Mechanical control of shrubs in a semiarid region of Argentina and its effect on soil water content and grassland productivity

Mechanical shrub control with roller choppers can be an inexpensive and non contaminant system for increasing grassland production in rangelands dry regions. A field experiment was carried out between October 1997 and October 2001 in the “Caldenal-Jarillal” botanic district of Argentina, a natural rangeland ecosystem with a high water deficit throughout much of the year. The trial was conducted on a Typic Ustortent and consisted of the following treatments: a control, the undisturbed natural condition (N), and rolled with (I) and without (R) interseeding of Panicum coloratum. Results showed that I and R improved soil water content within the upper 100 cm, dry matter production of grasses, amount of litter and water use efficiency as compared to N. The positive effect of rolling on soil water content was detected only in autumn months when water balance was positive. In summer months, when a negative water balance occurred, soil water content of rolled treatments was not different from that of the unrolled one. Consumptive water use was similar in rolled and unrolled treatments, and equivalent to the rainfall, reflecting the low soil water-holding capacity. The higher efficiency of water use in rolled treatments indicated that grasses were more efficient in using the consumed water. The I and R treatments had similar values of soil water content within the upper 100 cm, grass dry matter production, amount of litter and water use efficiency. However, a higher grass dry matter production in R than in I was noticed in part of the last year of this study. Grass dry matter production increased at the same rate in all treatments after 4 years, but litter remained constant in the unrolled treatment and decreased in the rolled ones. Mechanical shrub control with a roller chopper decreased shrub competition, thereby increasing the productivity of the ecosystem.