Spring Canola Critical Growth Stages for Water Management.

Sustaining irrigated agriculture in the U.S Southern Great Plains (SGP) requires low water using alternative crops. Since these alternative crops are competing for water with main cash crops (e.g. corn), understanding critical stages for water is very important for deficit irrigation management. Therefore, a field trial was conducted in 2015 and 2016 at the Agricultural Science Center at Clovis, NM to study effect of limited irrigation on three spring canola (Brassica napus L.) cultivars (H930, H955 and L140)). Irrigation treatments were 1). Full irrigation (FI), 2). No irrigation at vegetative stage (VS), 3). No irrigation at reproductive stage (RS) and 4). Dryland after crop establishment (DL). Seasonal pattern of biomass production indicated that VS recovered from water stress during reproductive stage and produced significantly higher biomass compared to RS and DL at harvest. Recovery of LAI and higher inflorescence biomass were mainly contributing for VS harvest biomass. Biomass in VS was similar to FI in 2015, the season with more rainfall, but was significantly lower in 2016, the drier season. In both years, seed yield of VS was similar to FI, but significantly higher compared to seed yield of VS and DL. Irrigating canola plants stressed during vegetative stage (VS), increased pods per plant, seed per pod and thousand seed weight compared to DL plants, but only seeds per pod and thousand seed weight of VS increased to be similar to FI canola. Harvest biomass, seed yield and yield parameters of all three cultivars responded similarly to irrigation treatments. Overall, reproductive stage of spring canola was more sensitive to water stress compared to vegetative stage. Thus, if water is limited, skipping irrigation during vegetative stage (VS) can save 33% of irrigation water at the loss of only 11% of seed yield.