Effects of application of poppy waste on spinach yields, soil properties, and soil carbon sequestration in southern Tasmania

Production of fresh market salad and lettuce in southern Tasmania has reduced soil organic carbon levels, resulting in the development of surface crusts, erosion, and poor water infiltration. Options for increasing soil organic carbon under this production system are limited by strict food safety protocols which prohibit the use of composts or 'animal'-based waste products. Poppy waste was identified as a suitable seed-free, inexpensive source of non-animal-based organic carbon. Trials were established on a Chromosol to evaluate the effects of poppy waste incorporation on soil organic carbon and production of Bocane spinach (Spinach oleracea). Application of 50200m 3/ha of poppy waste resulted in significant yield loss (up to 57%) of seedlings planted within 8 weeks following waste incorporation. It was speculated that yield loss resulted from nitrogen drawdown; however, soil analyses demonstrated that yield loss resulted from a combination of increased soil pH and soil salinity (EC). The 200m3/ha treatment increased soil pHwater from 7.2 before application to 8.5 and 7.7, at 4 and 22 weeks after application. Soil EC1:5 increased from 0.15dS/m before application to 0.45dS/m at 2 weeks after application, before returning to 0.15dS/m at 22 weeks. Application of poppy waste at 200m3/ha significantly increased soil organic carbon from 1.24% to 1.57%; however, applications at lower rates were not significant. The carbon sequestration efficiency from poppy waste to soil organic carbon was calculated to be approximately 0.20. © CSIRO 2009.