Impact of long-term trash blanketing and tillage prior to planting on soil carbon and sugarcane production

Green cane trash blanketing (GCTB) has been widely adopted in the Australian industry for more than 30 years. Trash contributes significant quantities of dry matter and carbon to the soil and this organic input is expected to improve sugarcane soil condition over the longer term. Understanding whether this has occurred is important as sequestering carbon in the soil is part of the Australian Government?s plan to achieve nett zero greenhouse gas emissions by 2050 and soil carbon is a key component of a healthy soil. A new sugarcane crop cycle was established at the long-term trash blanketing trial site at Mackay. Two minimum tillage treatments, bed renovation plus wavy disc (BRWD) and wavy disc only (WD), were imposed in order to evaluate their effect on productivity and soil C dynamics. Soil total C and total N, organic C (Walkey Black), total organic C (Heanes) and potassium permanganate oxidisable C (PPOC), were all measured prior to crop establishment and during the crop cycle. Soil C concentrations and stocks, apart from PPOC in the top two centimetres of soil, were either unchanged or higher in the burnt than the GCTB system. Sugarcane and sugar yield were significantly higher in the GCTB system in the first-ratoon crop, but not in the plant and second-ratoon crops. The BRWD tillage treatment produced significantly higher yields than WD. Soil in the WD system remained hard and compacted from the previous crop cycle. The lack of soil C accumulation under GCTB after three decades at the Mackay long-term site suggests that new approaches to trash management should be investigated.