Crop growth and water use under deep tillage

Page 1

2019

Crop growth and water use under deep tillage Authors: Murray Unkovich1, Michael Moodie2 Research Team: Todd McDonald, Mick Brady, Chris Davies 1 School Agriculture, Food and Wine, The University of Adelaide, 2Frontier Farming Systems Funded By: GRDC Project Title: Increasing production on sandy soils in low and medium rainfall areas of the Southern Region Peer Review: Tanja Morgan Key Words: barley, wheat, deep ripping, water use efficiency

Key Messages • • • •

Heads/m2 and grain yield were increased by deep tillage to 30cm but not 20cm Total crop water use was marginally increased by tillage to 30cm but could not account for all of the increase in grain yield Crops may have responded to deeper tillage by producing more tillers and increasing yield potential Water use efficiency was substantially increased by deep tillage, probably due to reduced bare soil evaporation under the better tillering crops

Background Sub-optimal productivity is commonly reported for the deep sands that make up 20 to 30% of the cropping soils in the low rainfall Victorian Mallee. There is evidence of unused soil water, despite an apparent absence of constraints commonly associated with sandy soils (e.g. non-wetting, soil acidity). Some studies have pointed to low fertility (abiotic and biological) in the subsoil layers and physical restriction of rooting depth as the most likely constraints to production. There is considerable interest in strategic deep tillage with/without agronomic amendments (fertilisers, organic amendments) to overcome both physical and nutritional constraints. While ripping approaches can overcome physical constraints, more intensive soil mixing (e.g. spading, inversion ploughing) can also be used to incorporate high nutrient organic amendments into the profile. In this paper we report on a study examining crop responses to deeper (20 and 30cm) tillage on a Mallee sandy soil at Ouyen from 2017 to 2019.

About the trial The trial at Ouyen had two key factors: (1) the depth of tillage, 7.5, 20 or 30cm, with all nutrients applied as a surface band at 7.5 cm depth, and (2) the frequency of the deep tillage, either just at the commencement of the trial in 2017 or annually (2017, 2018 and 2019). Each year plots all plots received 50 kg N through a combination of starter fertiliser (DAP S Z @ 62.5 kg/ha and Urea @ 65 kg/ha) banded below the seed and SOA @ 50 kg/ha top dressed in crop. The trial was sown to Spartacus barley on 29 May 2017 on a full profile of moisture due to 100 mm of rainfall falling in the month preceding sowing. Growing season rainfall in the subsequent two years was very low (Table 1). Crop water use was estimated as the difference between soil water (0-1.5m, 0-1m in 2017) at sowing and at harvest plus growing season rainfall. Table 1. Crops, sowing and harvest dates and growing season rainfall (GSR) at the Ouyen site.

Year Crop Sow Date Harvest Date GSR (mm) 2017 Spartacus barley 29/5/17 22/11/17 123 2018 Kord wheat 31/5/18 27/11/18 93 2019 Spartacus barley 27/5/19 29/11/19 88


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