Development, growth and water extraction of seeding lucerne grown on two contrasting soil types

Abstract

Dryland lucerne (Medicago sativa L.) was established at Lincoln University, New Zealand in two soils which differed in the plant available water content (PAWC). The high PAWC site is a silt loam soil with ~325 mm of water to 2.3 m. The low PAWC site had a very stony silt loam soil with only ~125 mm to 2.3 m. Both crops were sown on 10 October 2011 and established with 200 plants/m2 . The high PAWC site produced 2600 kg DM/ha shoot yield from sowing to 50% flowering compared with only 900 kg DM/ha at the low PAWC site. Both crops extracted water from the soil to a depth of ~1.2m, but the lucerne grown on the high PAWC soil extracted twice as much water to this depth. The water use efficiency (WUE) for both crops was 27.0 kg/DM/ha/mm of water used. The leaf appearance rate was 48 degree-­days per node (Tb=1°C) and was unaffected by site. Leaf area expansion rates exhibited a strong relationship with accumulated thermal time (R 2>0.94). Leaf area on the high PAWC site increased exponentially at about at 0.004 m2 leaf/m2 soil per degree­day, compared to the low PAWC site which increased linearly at a rate of 0.0009 m2 leaf/m2 soil per degree-day. Soil moisture extraction patterns indicated an extraction front velocity of 13 mm/day at both sites. Differences in lucerne yield were therefore fully attributable to differences in water extraction to a depth of 1.2 m