The effect of irrigation on barley root architecture, yield and water-use efficiency in vertic duplex soils. Marek Matuszek1*, Tina Botwright Acuña 1, David Parsons 1 and Marcus Hardie1 1
Tasmanian Institute of Agricultural Science, University of Tasmania Private Bag 54, Hobart 7001, Tasmania, Australia *corresponding and presenting author,
[email protected]
Summary Root-soil interactions have revealed to be an important factor in increasing yields and water-use efficiency of grain crops in hydraulically complex duplex soils. Strategic irrigation of barley was demonstrated to increase rooting depth of barley in vertic, duplex soils and as a result, had a positive influence on grain yield and water-use efficiency.
Introduction Water availability is an ever increasing issue for agricultural production around Australia. Therefore farmers need to improve traditional irrigation techniques in order to operate in an economical and environmentally sustainable manner. Duplex soils occupy a majority of southern Australian agricultural regions and can be difficult to irrigate due to hydraulic complexities particularly with a vertic, clay subsoil (Willatt and Olsson 1982). This project assesses how strategic irrigation can be used to overcome the complexities of duplex soils to maximise yield and water-use efficiency (WUE) of barley through maximising root depth and distribution.
Materials and Methods
Barley (cv. Gairdner) was grown under waterlogged, optimally irrigated and rainfed treatments in 5 replicates on a duplex soil in Southern Tasmania. Plants were sampled at maturity. Following harvest for yield, 1 m2 pits were excavated and root number, soil moisture and soil strength were measured on horizontal soil faces to a depth of 110 cm. Volumetric soil moisture was recorded in each treatment throughout the growing season with a Sentek EnviroSCAN to a depth of 110 cm. Soil, plant and weather data were collated to parameterise APSIM for the calculation of WUE.
Results & Discussion
Increased root depth significantly improved grain yield and WUE. Maximum rooting depth was greatest in the optimum treatment and shallowest in the rainfed treatment (Table 1). Root depth was associated with grain yield. The optimally irrigated treatment had the greatest yield, followed by the waterlogged and rainfed treatments, respectively. The optimally irrigated treatment had the greatest WUE. Even though the rainfed treatment had the poorest yield, WUE was greater that the waterlogged treatment (Table 1). Poor yield in the rainfed treatment was due to a reduced % fertile tillers and ear dry matter compared with the optimum and waterlogged treatments. Reduced yield in the waterlogged treatment was due to a significant decrease in ear dry matter and grains/ear, as a result of the plant producing higher number of tillers during recovery from waterlogging stress, which led to delayed ear maturation. (Robertson et al. 2009). As clay subsoil dries, penetration resistance increases eventually causing root growth to cease (Clark et al. 2003). Root growth was impeded in the rainfed treatment and reduced the exploration capacity of roots, limiting water availability for crop growth as found by Kirkegaard and Lilley (2007). Increased crack formation occurred as the soil dried, which become preferential pathways for water and roots, but may also increase water loss through deep drainage. Concentration of roots within these cracks can account for up to 80% of rooting systems, reducing available water and leading to an earlier onset of moisture stress (Pankhurst et al. 2002).
High soils strength and crack formation can be overcome by ensuring that soil moisture is optimal for root penetration though strategic irrigation. Not only does this provide the crops water requirements, but also leads to greater access to water deeper in the soil profile, which is vital for grain filling (Kirkegaard et al. 2007). Overcoming high soil strength by increased soil moisture was the major aim of the waterlogged and optimum treatments. Root data confirmed increased root depth under optimal and excess irrigation, compared with the rainfed treatment. Increasing the frequency of irrigation led to waterlogging, which is a potential issue in duplex soils (Willatt and Olsson 1982). The abrupt change in texture means there is a large contrast in the permeability of the two soil horizons (Tennant et al. 1992). The low permeability of the B horizon and the low water holding capacity of the A horizon makes the soils very prone to waterlogging, particularly under irrigation. Although the waterlogged treatment had a lower penetration resistance, root depth was shallower than the optimum treatment. As a result, access to available subsoil water towards the end of the growing season was limited as has been reported by Edwards (1992) and Gardner et al. (1992). Strategic irrigation of barley was demonstrated to have a positive influence on grain yield, rooting depth and distribution in vertic, duplex soils. Improved understanding of root -soil interactions can be used to develop more effective irrigation to increase yields and water-use efficiency of grain crops in these hydraulically complex soils. Table 1: Effect of irrigation on barley yield, % fertile tillers, ear dry matter, maximum rooting depth and WUE at final harvest Yield Fertile tillers Max Root Depth WUE Treatment Ear DM(g) (t/ha) % (cm) (kg/ha.mm) Waterlogged
5.49
84.9
0.81
110
15.9
Optimum
6.38
87.2
0.99
130
21.2
Rainfed
4.86
78.1
1.12
90
17.7
Lsd (P>0.05)
0.52
6.4
0.11
References
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