Subsoil macropore space of a transitional red-brown earth after either deep tillage, gypsum or both .I. Physical effects and short term changes

Abstract

This research aimed to improve understanding of the processes which cause deterioration of macropore space (volume and permeability of air-filled pores at -10 kPa matric potential), as well as providing some guidelines for improving management. This paper reports the effects of amelioration treatments on soil fragment sizes and horizon-of-origin, as well as the distribution of solid gypsum in the profile immediately after deep cultivation. The macropore space of the subsoil after initial winter cropping is described from measurements on soil cores collected from the experiment. The finer fragments from slotting at low speed resulted in smaller macroporosity than in the ripped soil. Macroporosity, permeability and organization of pore space generally increase with the amount of gypsum initially mixed with the soil. In spite of the smaller volume of soil disturbed by slotting than by ripping, the reduction in runoff was similar to the ripped soil when the gypsum application rate to the slotting was twice that applied to the ripped soil. Where no gypsum was applied to the slotted soil, slumping and swelling led to considerable loss of macroporosity formed by the initial deep tillage, as well as surface sealing by dispersed clay. Hence runoff from this treatment was similar to the unameliorated soil.