Benchmarking nitrous oxide emissions in deciduous tree cropping systems

Abstract

Abstract. Nitrous oxide (N 2 O) emissions contribute 6% of the global warming effect and are derived from the activity of soil-based microorganisms involved in nitrification and denitrification processes. There is a paucity of greenhouse gas emissions data for Australia's horticulture industry. In this study we investigated N 2 O flux from two deciduous fruit tree crops, apples and cherries, in two predominant growing regions in eastern Australia, the Huon Valley in southern Tasmania (Lucaston -apples and Lower Longley -cherries), and high altitude northern New South Wales (Orange -apples and Young -cherries). Estimated from manual chamber measurements over a 12-month period, average daily emissions were very low ranging from 0.78 g N 2 O-N ha -1 day -1 in the apple orchard at Lucaston to 1.86 g N 2 O-N ha -1 day -1 in the cherry orchard in Lower Longley. Daily emissions were up to 50% higher in summer (maximum 5.27 g N 2 O-N ha -1 day -1 at Lower Longley) than winter (maximum 2.47 g N 2 O-N ha -1 day -1 at Young) across the four trial orchards. N 2 O emissions were~40% greater in the inter-row than the tree line for each orchard. Daily flux rates were used as a loss estimate for annual emissions, which ranged from 298 g N 2 O-N ha -1 year -1 at Lucaston to 736 g N 2 O-N ha -1 year -1 at Lower Longley. Emissions were poorly correlated with soil temperature, volumetric water content, water filled porosity, gravimetric water content and matric potential -with inconsistent patterns between sites, within the tree line and inter-row and between seasons. Stepwise linear regression models for the Lucaston site accounted for less than 10% of the variance in N 2 O emissions, for which soil temperature was the strongest predictor. N 2 O emissions in deciduous tree crops were among the lowest recorded for Australian agriculture, most likely due to low rates of N fertiliser, cool temperate growing conditions and highly efficient drip irrigation systems. We recommend that optimising nutrient use efficiency with improved drainage and a reduction in soil compaction in the inter-row will facilitate further mitigation of N 2 O emissions.

Uptake efficiency and internal allocation of nitrogen in apple trees

“…As the pre-harvest fertiliser treatment commenced in late October, there was a considerably longer period of time for N uptake to occur. Within this longer time period there is greater potential for N loss through either leaching or gaseous loss of N as N 2 or N 2 O (Swarts et al, 2016). Thus it is important to interpret our results in the context of leachates being reused in contrast to the field situation of leachates being lost, once below the root zone.…”

Nitrogen Use Efficiency, Allocation, and Remobilization in Apple Trees: Uptake Is Optimized With Pre-harvest N Supply

“…The latter factor is also consistent with the much-reduced NUpE of postharvest fertilizer application observed in our study, where the amount of N taken up is likely to be limited by the lessened transpirational pull associated with the reduced sap flow activity (Fujii and Kennedy, 1985) later in the season. Although there were indications of some fertilizer N remaining in the soil at 2018 dormancy (Table 2), it is very likely that some of that not utilized by the trees may have been lost to the immediate environment either via leaching (Hardie et al, 2018) taken up by roots of neighboring trees or undergone a transformation to other N forms, e.g., by denitrification to nitrous oxide (Swarts et al, 2016), dinitrogen gases, or by dissimilatory nitrate reduction to ammonium (Giblin et al, 2013). • Represents degree of and angle, the parameter was measured in "Brix degree angle".…”

“…However, N fertilizer can be oversupplied in production systems due to the perceived costeffectiveness of achieving increased yield per unit area (Drake et al, 2002;Neilsen et al, 2009). In apple orcharding, this can cause reductions in fruit quality (Carew, 2000) and low use efficiency of N resources (Neilsen et al, 2001a), contributing to the pollution of underground water supplies (Neilsen and Neilsen, 2002), and emissions of the potent greenhouse gas nitrous oxide (Freney, 1997;Swarts et al, 2016). Nitrogen is also commonly applied post-harvest either via fertigation or the application of foliar-applied urea, with the aim of increasing N reserves in storage organs (i.e., buds, spurs, and roots) and for faster decomposition of the leaf litter material (Han et al, 2011).…”

Climate change mitigation beyond agriculture: a review of food system opportunities and implications

“…1.3 and 8.0 Pg CO 2 eq yr −1 (Sommer and Bossio, 2014;Paustian et al, 2016) Horticulture (fruit, vegetable, perennials) Very few reviews exist for horticulture climate mitigation, a clear need for future research. Many noted strategies include: soil amendments, crop residue removal, cover crops, organic production, water use efficiency and improved drainage and compaction prevention in tree crops, many of which may also be relevant for other cropping systems (Aguilera et al, 2013;Congreves and Van Eerd, 2015;Rezaei Rashti et al, 2015;Swarts et al, 2016;Niles et al, 2017).…”