Sustainable nutrient supply what does the soil tell us? Loretta Garrett, Simeon Smaill, Peter Beets, Peter Clinton, Mark Kimberley
Importance of NZ planted forest soils Expectation for economic growth Emergent shift towards high value sustainably produced primary products Rotation number for NZ planted forests 36% in 2 nd rotation, 20% in 3 rd rotation, 4% in 4 th rotation
Is soil nutrient supply sustainable? Key question to address are: Does soil fertility decline with each successive rotation? Is there an impact of the level of organic matter removal at harvest on productivity and soil fertility? Is there an impact of fertiliser addition on productivity and soil fertility?
Long-term trials Organic matter removal Fertiliser amendment 6 sites, established 1986 Whole tree harvest and forest floor removed Kinleith Tarawera Stem only harvest
Tarawera tree growth results 300 Index 30 25 20 No fert Fert Organic matter removal (T ha -1 ) Nitrogen removal (kg ha -1 ) 15 FF WT SO Whole tree + Forest Floor removed Harvesting Whole treatment tree removed Stem only removed 54.1 30.2 0 507.8 157.9 0 No significant difference between treatments
Tarawera Case Study: Predicting productivity gap with CABALA Volume (m 3 /ha) Stand volume by lever 900 Actual 800 Depth 700 No Stone 600 Fertiliser Organic Matter 500 Opt 400 300 200 100 0 1 3 5 7 9 11 13 15 17 19 21 23 25 Age (yrs) Meason et al., (2015). Quantifying the productivity gap.
Tarawera soil results Stem only removal and no fertiliser addition 0-10 cm 1989 2014 Total C (%) Total N (%) Bray P (mg%) K (cmol/kg) Ca (cmol/kg) Mg (cmol/kg) Na (cmol/kg) CEC (cmol/kg) BS (%) Low Low Medium Low Low Medium Low Medium Medium (ns) (ns) (ns) (ns) (ns) (ns) Significant (ns) Not significant
Tarawera soil results Organic matter management no fertiliser addition Depth (cm) Treatment Bulk density (g/cm 3 ) Total C (%) Total N (%) Total P (mg%) Bray P (mg%) 0-10 FF a a a a a WT a b ab a a SO a b b a a No change in cations (K, Ca, Mg, Na) or CEC 10-20cm soil depth same trend 20-30 cm soil depth Total N decreased but not Total C
Tarawera soil results Change with the addition of fertiliser Depth (cm) Bulk density (g/cm 3 ) Total C (%) Total N (%) Total P (mg%) Bray P (mg%) K (cmol/ kg) Ca (cmol/k g) Mg (cmol/k g) Na (cmol/k g) CEC (cmol/k g) 0-10 none none none none none 10-20 none none none none none none none 20-30 none none none none none none none none
Tarawera soil results Does fertiliser addition compensate for the effect of the forest floor removal treatment? 3.0 Total C concentration (g/cm 3 ) Total C (%) 2.5 2.0 1.5 1.0 0.5 0.0 FF WT SO Treatment Treatment Unfertilised Fertilised 0.16 Total N concentration (g/cm 3 ) Total N (%) 0.14 0.12 0.10 0.08 0.06 0.04 0.02 Unfertilised Fertilised Fertiliser amendment was unable to recover soil carbon and nitrogen 0.00 FF WT SO Treatment Treatment
Summary and comparison to Woodhill Tarawera No tree growth response to organic matter or fertiliser treatments FF treatment reduced soil C and N Woodhill Tree growth decline with FF treatment and tree growth increase from fertiliser addition Fertiliser amendment was unable to recover FF removal treatment soil C and N to SO removal treatment Fertiliser addition increased soil C and N Fertiliser addition increased soil Total P and Bray P Fertiliser addition decreased soil Total P and Bray P
How do these results line up with international findings Meta analysis of long-term trial sites consequences of removing harvesting residues on forest soils and tree growth Achat, et al., 2015. Forest Ecology and Management 348, 124-141.
Meta-analysis on harvest removals Removing harvest residues, especially forest floor and tree foliage compared to stem only removal: o Decrease in tree growth magnitude change generally low (e.g. volume or basal area or biomass decrease 3 7%) o Decrease in soil organic matter, total nitrogen, total phosphorus and total calcium, available soil phosphorus, cation exchange capacity and base saturation However, results were variable due to: o Data available and clustering of experiments o Differences in harvest treatments, tree species o Site factors o Sampling time within the rotation there was evidence that soil fertility may recover as the trees mature
Summary The end of rotation results from Tarawera and Woodhill provide: o Insight into future productive potential of NZ planted forests o Rare data for testing NuBalM Nutrient Balance Model Under stem only harvest operations soil fertility is generally maintained in the second rotation The addition of fertiliser is beneficial to soil fertility but site factors may result in no tree growth response
Summary Tarawera will be an interesting site to reestablish and test the impact of another rotation on soil fertility How many rotations will it take to see nutrient limitations on productivity? Site water limitation SO Site nutrient limitation WT FF 1 2 3? Rotation Number
http://research.nzfoa.org.nz/ www.scionresearch/gcff Loretta Garrett loretta.garrett@scionresearch.com 13 May 2016