Deep soils modify environmental consequences of increased nitrogen fertilizer use in intensifying Amazon agriculture

Kathijo Jankowski,Christopher Neill,Ciniro Costa,Michael T Coe,Darlisson Nunes,Eric A Davidson,Gillian L Galford,Paul Lefebvre,Marcia N Macedo,Carlos E P Cerri,Christine O’Connell,Leonardo Maracahipes Santos,Richard Mchorney

doi:10.1038/s41598-018-31175-1

Abstract

Agricultural intensification offers potential to grow more food while reducing the conversion of native ecosystems to croplands. However, intensification also risks environmental degradation through emissions of the greenhouse gas nitrous oxide (N2O) and nitrate leaching to ground and surface waters. Intensively-managed croplands and nitrogen (N) fertilizer use are expanding rapidly in tropical regions. We quantified fertilizer responses of maize yield, N2O emissions, and N leaching in an Amazon soybean-maize double-cropping system on deep, highly-weathered soils in Mato Grosso, Brazil. Application of N fertilizer above 80 kg N ha−1 yr−1 increased maize yield and N2O emissions only slightly. Unlike experiences in temperate regions, leached nitrate accumulated in deep soils with increased fertilizer and conversion to cropping at N fertilization rates >80 kg N ha−1, which exceeded maize demand. This raises new questions about the capacity of tropical agricultural soils to store nitrogen, which may determine when and how much nitrogen impacts surface waters.

Highlights

We quantified fertilizer responses of maize yield, N2O emissions, and N leaching in an Amazon soybeanmaize double-cropping system on deep, highly-weathered soils in Mato Grosso, Brazil
The vast majority of studies of the environmental consequences of fertilizer-intensive cropping are from temperate regions, the most rapid and extensive intensification of crop agriculture occurs in tropical forest and savanna regions[1,12,13,14]
Because much of this tropical cropland expansion and intensification occurs on old, highly weathered soils, the environmental consequences of increasing N fertilizer use may differ markedly from those observed in temperate cropping systems on more recently-developed, less weathered soils[1,4,17]

Summary

Introduction

We quantified fertilizer responses of maize yield, N2O emissions, and N leaching in an Amazon soybeanmaize double-cropping system on deep, highly-weathered soils in Mato Grosso, Brazil. We used the results of the field experiment to estimate the distribution and magnitude of N2O emissions and N leaching across the Amazon-Cerrado cropping region based on soils and the current area of soybean-corn double-cropping.

Results

Conclusion