Submitted to: International Soil Tillage Research Organization Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/5/2003
Publication Date: 6/22/2003
Citation: Brown, G.G., Oliveira, L., Norton, L.D., Alberton, O., Brandao, O., Saridakis, G.P., Torres, E. 2003. Quantifying scarab beetle-grub holes and their volume as affected by different tillage and crop management systems. In: International Soil Tillage Research Organization Proceedings. CDROM. Interpretive Summary: Organisms living in soils often are pests because they feed on roots and damage plants, but they can also have a beneficial effect on soil hydrology by creating pathways for water to enter the soil that would not otherwise be present. This is particularly important in large rainfall events that cause soil erosion by water. The effect of soil organisms is minimized in conventional tillage systems because burrows are destroyed by the tillage. We measured the burrows created by white grubs (scarab beetles) in a long-term no-tillage experiment and compared them to those found in conventional tillage and chisel plowing systems at the National Soybean Research Center of EMPRAPA in Brazil. No-till was found to have many more grub holes than conventional tillage, with almost 10 times the volume of pore space. The burrows alter the hydrologic function of the soil in both conventional and no-tillage systems and aid in the decomposition of residues and nutrient cycling. This research impacts scientists studying and modeling macropore development and effects on runoff, soil loss and water quality. Better understanding of the creation and properties of these burrows under different tillage systems impacts scientists, conservation planners, and extension service personnel as they assess the benefits of no-till systems when white grubs or other burrowing organisms are or are not present.
Technical Abstract: Scarab beetle (white) grubs are not only pests, but they can also have important beneficial effects on the soil by burying litter and creating vertical holes that act as preferential pathways for water infiltration in large storms. With the aim of studying the effect of white-grubs on the physical and hydrological properties of an Oxisol at the Embrapa Soybean Research Station, the number, diameter and depth of beetle-grub holes opened at the soil surface were measured in a long-term (13-year old) tillage and cropping systems trial. The measurements were performed in experimental plots submitted to conventional (CT) and no (NT) tillage, or scarification (chisel-plowing) every 3 yr. All plots were either in continuous double-cropping (wheat/soybean) or a rotation including lupine/maize-oats/soybean-wheat/soybean. The results revealed that the beetle grub holes were much more abundant in NT (8,8-9,6 m-2) than CT (0,7-1,3 m-2) plots, where tillage destroys them. The largest and deepest holes were also found in NT (up to 33,5 mm diameter and 117 cm deep). Consequently the total volume of pores opened in NT was up to almost 10 times greater than in CT. However, the mean diameter and depth of the few holes found in CT tended to be greater than in NT, probably due to the looser soil, and/or the need of the larvae to go beyond the plow layer. The potential beneficial effects of these holes to soil function (water infiltration, porosity, litter decomposition, creation of fertile niches in the soil) and their effects on the biodiversity of other soil and litter invertebrates in NT systems deserves further attention. These will be studied by researchers at Embrapa Soybean, in collaboration with the USDA-ARS National Soil Erosion Laboratory.