Response of Contrasting Alfalfa Cultivars to Summer Irrigation in Tasmania, Australia.

Alfalfa (Medicago sativa L.) has been identified as a potential summer forage for Tasmanian dairying.  In the cool temperate environment of Tasmania an important factor in deciding to irrigate summer forages is the expected production response, known as marginal water use efficiency (WUE) of the species or cultivar.  This study aimed to identify the effect of cultivar on the marginal WUE of alfalfa in Tasmania. 
Dry matter (DM) yield of four alfalfa cultivars grown with or without irrigation over the 2007/08 spring and summer were monitored at Elliott, Tasmania (41°4’48”S, 145°46’12” E, 1200mm annual rainfall, Humic Eutrodox soil).  Cultivars chosen to represent a wide range of fall dormancy (FD) consisted of DuPuits (FD3), Grasslands Kaituna (FD4.5), SARDI-7 (FD7) and SARDI-10 (FD10). 

Under rain-fed conditions fall-dormant cultivars produced significantly more (P<0.05) DM than fall-active cultivars. There was no significant difference (P>0.05) in DM yields between cultivars when irrigated.  Differences in marginal WUE existed between alfalfa cultivars with SARDI-10 having significantly greater (P<0.05) marginal WUE than Grasslands Kaituna or SARDI-7 (Table 1). 
Although there were differences in marginal WUE between alfalfa cultivars, it is concluded from this study that little benefit can be gained from irrigating one alfalfa cultivar in preference to another as irrigated yields were similar among cultivars.  However, it is recommended that alfalfa be irrigated in preference to perennial grass pastures, as marginal WUE is substantially higher than the industry average pasture response of 10 kg DM mm^-1.

Table 1. Yield and marginal water use efficiency (WUE) over spring and summer of four alfalfa cultivars grown with or without irrigation at Elliott, Tasmania, Australia

Cultivar	Raingrown Yield (kg ha-1)	Irrigation Yield (kg ha-1)	Marginal WUE (kg mm-1)
DuPutis	7576	13952	18.75
Grasslands Kaituna	7817	13723	17.37
SARDI-7	7243	13171	17.43
SARRD-10	6791	14039	21.32
LSD (P=0.05)	548	ns	3.28

See more from this Division: A06 International Agronomy
See more from this Session: Advances in International Agronomy (includes Graduate Student Competition) (Posters)

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