APPRAISAL OF THE SNAP MODEL FOR PREDICTING NITROGEN MINERALIZATION IN TROPICAL SOILS UNDER EUCALYPTUS

Philip James Smethurst,Ana Paula Pulito,Clayton Alcarde Alvares,Keryn Paul,Simone Gomes,José Leonardo De Moraes Gonçalves,José Carlos Arthur Júnior

doi:10.1590/01000683rbcs20140379

Abstract

The Soil Nitrogen Availability Predictor (SNAP) model predicts daily and annual rates of net N mineralization (NNM) based on daily weather measurements, daily predictions of soil water and soil temperature, and on temperature and moisture modifiers obtained during aerobic incubation (basal rate). The model was based on in situ measurements of NNM in Australian soils under temperate climate. The purpose of this study was to assess this model for use in tropical soils under eucalyptus plantations in São Paulo State, Brazil. Based on field incubations for one month in three, NNM rates were measured at 11 sites (0-20 cm layer) for 21 months. The basal rate was determined in in situ incubations during moist and warm periods (January to March). Annual rates of 150-350 kg ha-1 yr-1 NNM predicted by the SNAP model were reasonably accurate (R2 = 0.84). In other periods, at lower moisture and temperature, NNM rates were overestimated. Therefore, if used carefully, the model can provide adequate predictions of annual NNM and may be useful in practical applications. For NNM predictions for shorter periods than a year or under suboptimal incubation conditions, the temperature and moisture modifiers need to be recalibrated for tropical conditions.

Highlights

A quantitative understanding of nitrogen (N) pools and fluxes can underpin improved N fertiliser management in plantation forestry (Smethurst and Nambiar, 1990; Smethurst et al, 2004; Corbeels et al, 2005; Laclau et al, 2010) and agriculture (Keating et al, 2003; Manzoni and Porporato, 2009; Sansoulet et al, 2014; Thorburn et al, 2010)
The Soil Nitrogen Availability Predictor (SNAP) model predicts daily and annual rates of net N mineralization (NNM) based on daily weather measurements, daily predictions of soil water and soil temperature, and on temperature and moisture modifiers obtained during aerobic incubation
The SNAP model predicted daily soil temperatures, which were averaged for each 3 month period for comparison with field measurements

Summary

Introduction

A quantitative understanding of nitrogen (N) pools and fluxes can underpin improved N fertiliser management in plantation forestry (Smethurst and Nambiar, 1990; Smethurst et al, 2004; Corbeels et al, 2005; Laclau et al, 2010) and agriculture (Keating et al, 2003; Manzoni and Porporato, 2009; Sansoulet et al, 2014; Thorburn et al, 2010). Net N mineralization (NNM), a key component of the N cycle, can be measured reliably using an unsophisticated in situ core technique (Raison et al, 1987) This technique is labour-intensive, which often precludes its use in N cycling research or fertiliser management. Soil water and temperature were predicted for field conditions using simple empirical sub-models calibrated for 18 sites in southern Australia. These soil and water predictions were used to adjust the basal NNM rate from which daily rates in the field could be estimated. The SNAP model was most recently used at the headwater catchment scale as a component to understand and model the pools and fluxes of mineral N in soil, ground water and stream water (Smethurst et al, 2014)

Objectives

Methods

Results

Conclusion