GHG Implications of no-till irrigated farming systems - Keytah

Date Issued:2009-06-30

Abstract

Keytah is an irrigated cotton and grains farming operation west of Moree in Northern NSW. The

total area of the property is 24 000 hectares of which 10 400 hectares is irrigated cotton, grown in

rotation with wheat. During a normal season only half of the irrigated area is cropped at any one

time with the other half maintained as a bare fallow. The farming system includes a summer cotton

crop, planted in October and followed by a winter wheat crop planted in May and harvested in

November. After the winter wheat crop a fallow of approximately 12 months takes place before

cotton is replanted back in October. The farming system incorporates 60” beds where cotton is

usually grown in two rows 30” apart or more recently in a single row where water supplies are

limiting. In comparison the wheat is grown in 4 rows on the same 60” beds at a spacing of 15”.

Regardless of the planting system adopted different plant lines are maintained between the summer

and winter crop options. All tractors have been extended to operate on 120” (i.e. 3 m) centres.

In a normal irrigation season Keytah relies on 7 to 7.5 ML/Ha of water for irrigation which is applied

by surface (furrow) irrigation and two lateral move irrigators. Water is sourced from the Gwydir and

Mehi Rivers and is pumped into on farm storages before being distributed to the field for irrigation.

In response to limited irrigation supplies (1 ML/Ha) in 2007 / 2008, a radical change in farming

practices is currently being pursued to establish and produce a cotton crop. Previously the variation

in soil properties across the farm has been identified via an EM survey. This survey was conducted

when the soil was relatively close to field capacity. In an attempt to identify fields which had

adequate soil moisture for planting cotton, an EM survey of the farm was again conducted to

identify areas of high soil moisture content. The EM survey identified 2 fields side by side where one

field had an estimated increase in soil moisture of 40% soil moisture. This increase in soil moisture

was attributed to no tillage over the fallow period.To assess the benefits of farming system changes in terms of energy and GHG emissions, 3 scenarios

were developed from actual crop history data and evaluated using the energy assessment software,

EnergyCalc.developed by the National Centre for

Engineering in Agriculture to assess total on farm energy use and the associated GHG emissions. The

three scenarios that were developed to assess farming practices on Keytah included:

i) a benchmark of energy use from 2000,

ii) current practices or reduced tillage and

iii) progression towards zero till farming methods

Each scenario was developed from previous farm records of field K8 (in 2000) and current crop

records of K8 and C16 (reduced tillage) and K13 and C17 (towards zero till). Farm practices were also

confirmed via an initial site visit.

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