Carbon Sequestration in Kiwifruit Orchard Soils at Depth to Mitigate Carbon Emissions

Management practices designed to increase carbon sequestration via perennial tree crops are potential tools to mitigate the consequences of climate change. Changes in orchard management could enable growers to meet eco-verification market demands for products with a low carbon footprint and potentially exploit the emerging business opportunity in carbon storage, while enhancing the delivery of ecosystem services that depend on soil carbon stocks. However, there is no standard methodology to verify any potential claims of carbon storage by perennial vine crops. We developed a robust methodology to quantify carbon storage in kiwifruit orchards. Soil carbon stocks (SCS) were determined in six depth increments to 1m deep in two adjacent kiwifruit blocks, which had been established 10 ("young") and 25 ("old") years earlier. We used a space-for-time analysis. Our key results were the young and old kiwifruit block stored about 139 and 145tC/ha to 1m depth. Between 80-90 percent of the SCS were stored in the top 0.5m, and 89-95 percent in the top 0.7m; there was no significant difference between the SCS in row and alley to a depth of 0.5m; a CV of 5-15 percent indicates that 4-10cores are needed for 80 percent confidence in the estimated SCS; we recommend separating each core into the depths 0-0.1, 0.1-0.3, 0.3-0.5, and 0.5-1m to allow the assessment of SCS dynamics; we detected a weak spatial pattern of the SCS only for the old kiwifruit block with a range of about 3m. A sampling bay along a vine row should have a maximum length of 3m. We then assessed SCS in more than sixty kiwifruit orchards throughout New Zealand. They stored on average 174.9 +/- 3tCha(-1) to 1m depth. On average, 51 percent of the SCS down to 1m depth were stored in the top 0.3m, which is the standard depth according to the Kyoto protocol. About 72 percent of the SCS to 1m depth were captured when increasing the sampling depth to 0.5m. These results underscore the necessity to analyze SCS in an orchard to at least 0.5m deep. Using the same methodology to 1m deep, we determined SCS in two wine grape vineyards on shallow, stony alluvial soils. We found a difference between vineyard and adjacent pasture SCS of nearly 16t/ha. As the vines are 25years old, this equates to carbon sequestration rates of 640kgha(-1)yr(-1). Our results of the space-for-time analysis also showed that all sequestration had occurred below 0.5m. Therefore, we decided to sample C to a greater depth. In a 30-year old kiwifruit orchard and an adjacent pasture, SCS was measured to 9m deep. In the kiwifruit orchard, we found a sequestration rate of 6.3tons of C per hectare per year greater than in the adjacent pasture that was the antecedent land use.