Preliminary investigation of clay soils' behaviour under furrow irrigated cotton

Abstract

Six experimental sites were selected, in the Namoi Valley, N.S.W., all on self-mulching cracking clay soil, to provide a variety of both management practice and length of time under cotton. Within each of the sites randomly located plots were positioned to cover both wheel-track and non-wheel-track areas. The design allowed assessment of both during-season effects caused by tractor wheels and between-site effects. Neither soil physical status (as measured by soil water extraction, air permeability and recovery of air-filled pores) nor yield was influenced by during-season tractor passes. However, non-wheel areas had significantly taller plants and more green cotton bolls per plant than wheel-influenced areas. Pronounced differences between sites in both soil physical status and cotton growth and yield were measured. For those sites in their first year of cotton there was greater soil water extraction, greater air permeability and more rapid recovery of air-filled porosity. They also produced up to 30% more yield in comparison with sites growing cotton for 8-17 years. At no site did any evidence arise to show 'ploughpan' or 'hardpan' formation.