Soil Organic Matter Management: The Roles of Residue Quality in C Sequestration and N Supply - Sustainable Management of Soil Organic Matter - page 104

F.A. Robertson and P.J.Thorburn Crop Residue Effects on Soil C and N Cycling

3.1

Crop Residue Effects on
Soil C and N Cycling under
Sugarcane

F.A. R OBERTSON 1

AND P.J. T HORBURN 2

1
CRC for Sustainable Sugar Production,BSES,PMB57, Mackay
MC, Qld 4740; and 2 CSIRO Tropical Agriculture, 306CarmodyRd,
St Lucia, Qld 4067, Australia

Introduction

In the Australian sugar industry, there is a progressive move away from
burning sugarcane ( Sacharum spp.) trash (green and senesced leaves)
before and/or after harvest (burnt system), to the green cane trash blanket-
ing (TB) system, where trash is retained on the soil surface and cultivation
is greatly reduced. Adoption of the TB system is seen as an important move
towards a more sustainable production system. When sugarcane trash is
burnt, > 80% of the organic matter and nutrients in the trash are lost
(P. Larsen and R. Mitchell, unpublished data). Conversely, with retention
of trash, nutrients and organic matter may be accumulating in the soil,
which has led to speculation that fertilizer applications should be reduced.
The effects of these management changes on the fertility of the canelands,
however, are largely unknown. This research was undertaken to investigate
the effects of sugarcane trash management (burnt or TB) on indicators of
short- and long-term soil C and N cycling. The implications of this cycling
for fertilizer management are discussed.

Methods

Burnt and TB systems were compared in five field experiments at three
locations with widely differing climates and varying crop ages (Table 3.1.1).
The experimental treatments, established at the time of planting, were
(i) burnt: trash burnt, soil cultivated to 150 mm depth after harvest and