THE EFFECT OF URBAN REFUSE COMPOST AND DIFFERENT TRACTORS TIRES ON SOIL PHYSICAL-PROPERTIES, SOIL-EROSION AND MAIZE YIELD

Application of urban refuse compost to agricultural soil could help to solve municipalities' problems related to the increasing production o f waste only if soil property improvement and environmental conservati on can be demonstrated. The use of low-pressure tractor tyres is anoth er proposal in modem agriculture for reducing soil compaction. This st udy thus aimed to detect the effects of both compost and low-pressure tractor tyres on soil loss, runoff, aggregate stability, bulk density, penetrometer resistance and maize (Zea mays L.) yield. A 3-year field experiment was carried out on a hilly (15% slope) clay loam soil in c entral Italy. Twelve plots (200 m(2) each) were monitored with tipping -pot devices for runoff and soil erosion measurement. Treatments were: compost addition (64 Mg ha(-1)), mineral fertilisation, use of low-pr essure tyres, use of traditional tyres, with three replicates, in a fu lly randomised block design. Compost was applied once at the beginning of the experiment. Runoff reduction due to compost ranged between 7 a nd 399 m(3) ha(-1) during seasons, while soil erosion was reduced betw een 0.2 and 2.4 Mg ha(-1). Mean weight diameter (MWD) of stable aggreg ates, measured on wheel tracks, increased by 2.19 mm, then progressive ly decreased. Compost significantly increased bulk density by 0.08 Mg m(-3) due to its inert fraction content. This effect was less evident in the second and third year, probably due to harrowing. Maize yields were slightly, but significantly, reduced in composted plots by 1.72 M g ha(-1) in the third year. Low-pressure tyres significantly reduced s oil loss in the third year by I Mg ha(-1). Furthermore, they did not s ignificantly influence runoff volumes and soil structural stability Lo w-pressure tyres or compost addition were singly able to prevent an in crease in penetrometer resistance due to agricultural machinery traffi c. Low-pressure tyres increased the maize yield during the 3 years and the difference (0.4 Mg ha(-1)) became significant in the third year. In conclusion results shaw the positive lasting effect of compost in a meliorating soil physical properties and reducing runoff and soil eros ion. Low-pressure tyres appear justifiable both for the observed incre ase of grain production and reduction of soil compaction. This latter effect is, nevertheless, masked by compost addition which is also able to reduce penetrometer resistance. Further research is required to ex plain the causes of the slight inhibition of grain yield observed when compost was compared with mineral fertilisation. (C) 1998 Elsevier Sc ience B.V. All rights reserved.