EFFECT OF SEWAGE SLUDGE AND SAWDUST IN ASSOCIATION WITH HYBRID RYEGRASS (Lolium × hybrydum HAUSSKN.) ON SOIL MACROAGGREGATES AND WATER CONTENT

Chilean soils degradation is a serious problem affecting directly the productivity of most of the crops. Some evidence indicates sewage sludge can improve soil physical properties, especially when combined with sawdust. The objective of this work was to evaluate the effect of different mixtures of sewage sludge (LU) and sawdust (RA) on water-stable aggregates and available water content of a degraded Alfisol cropped with hybrid ryegrass (Lolium × hybrydum Hausskn.), under greenhouse conditions. The experimental design was a completely randomized with a factorial arrangement of 2 × 9 (ryegrass × rates of sludge and sawdust). Treatments were 25 and 50 Mg LU ha^-1 mixed with 10, 25, and 50 Mg RA ha^-1. Ratio mixtures of LU/RA were set in pots with hybrid ryegrass. Soil available water content (AW), percentage of macroaggregates (MA) and water-stable aggregates (AWD) were evaluated. Ryegrass aboveground biomass was also measured. Mixtures of LU/RA amended to the soil increased MA and AWD, an effect that was most evident at 50 Mg ha^-1. The AW value was greater when LU was amended to 50 Mg ha^-1 mixed with RA at doses of 10, 25, and 50 Mg ha^-1. There was greater aboveground biomass of hybrid ryegrass, directly related to increasing doses of LU and RA in the mixtures. The addition to soil of both organic residues combined, LU and RA, improved the physical parameters studied, especially in the presence of hybrid ryegrass.

Keywords
Soil aggregation, biosolids, remediation, organic wastes, degraded soil