# Presentation: 228081

## Terrestrial Processes and Fertilizer N Fate in Southern Pine Plantations:  Needs for Research and Modeling  

**Eric D. Vance**
**National Council for Air and Stream**
**Improvement (NCASI)**
**Research Triangle Park, NC**

## Questions about Fertilizer Nitrogen Fate in Pine Plantations

**Increasing management intensity**
**Fertilizer use, practices**
**Tree uptake, understory, forest floor**
**Potential impacts**
**Water, air, greenhouse gases**
**Minor relative to other land uses **
**Frequency and extent of use may change **
**Need science-supported documentation**

## Area of Pine Plantations Fertilized Annually in the Southeastern U.S.(Fox et al., 2007) 

## Southern Pine Fertilizer Use(Fox et al. 2007, pers. com.)

**0.5 million ha (1.2 million ac) fertilized (2004)**
**81,000 ha (200,000 ac) at establishment**
**405,000 ha (1 million ac) at midrotation**
**At establishment**
**224 kg ha****-1**** DAP (200 lb ac) **
**Supplies 40 kg ha****-1**** N **
**Mid-rotation**
**140 kg ha****-1**** DAP + 431 kg ha****-1**** urea**
**Supplies 223 kg ha****-1**** N **

## Characteristics of Most Forest  Nitrogen Fate Studies

**Not comprehensive – focused on selected components**
**Miss short-term source-sink windows**
**Few long-term studies**
**Few studies linking terrestrial processing and water quality**
**Few studies use labeled N - difficult to directly trace fate**

## Examples of Factors Influencing Fertilizer N Fate

**Tree fertilizer use efficiencies**
**23% to 100% across 14 midrotation installations (Ducey and Allen 2001)**
**Forest floor an N source or sink?**
**Volatile N loss**
**IPCC default - 1.25% for N****2****0 (agricultural studies)**
**< 1% volatile N loss from urea with immediate simulated rain, up to 58% loss without (Kissel et al. 2004)**

## Young (3- 4-yr old) loblolly pineFL Lower C. P. (Baker et al. 1974)

**Single and split applications (May/Aug.)  **
**0, 112, 224 kg N ha****-1**
**20% “recovery” after 2 yr**
**Trees, understory, soil (0.3 m)**
**No effect of application rate**
**30% with split applications **
**Herbaceous recovery up to 50% of total**

## 11-yr old slash pine, FL Lower CP  (Mead and Pritchett 1975a,b)

**Labeled NH****4****SO****4**** around single trees**
**0, 56, 224 kg N ha****-1**** equivalent **
**50% recovery after 2 yr**
**25% trees (41% in foliage), 15% roots **
**24% litter and soil to 2 m**
**Forest floor retention decreased from 20% to 9% from 3-6 weeks due to leaching and/or gaseous loss**

## Univ. GA Consortium for Accelerated Pine Production Studies (CAPPS) (Will et al. 2006)

**13-yr annual fertilization, comp. control, Piedmont, Lower Coastal Plain**
**72 kg N ha****-1**** yr****-1****, 863 kg N total**
**System recovery – 89%**
**Aboveground biomass – 35%**
**Forest floor – 33%**
**Mineral soil – 21%**

## Terrestrial Data and Models are Needed

**Extrapolate across sites, treatments **
**Difficult to replicate**
**Require process-level understanding**
**General guidelines**
**Conservative range of suitable practices**
**Site-practice combinations requiring additional data, potential mitigation  **
**Test and refine assumptions and projections at selected sites**

## Research and Modeling Needs: Management Practices and Trends 

**Quantity, type, and timing of application**
**Synchrony**
**Biotic – vegetation, microbial activity**
**Management - thinning**
**Abiotic – precipitation **
**Management intensity**
**Application frequency**
**Competition control**
**Rotation length**
**Residue removal**

## The Use of Models in Practice 

**Detailed models will not be used by most landowners**
**Basis for general guidelines**
**Conservative default assumptions**
**Range of practices, site categories **
**Contributions at the landscape scale**