Water use efficiency of fodder beet crops

Abstract In New Zealand, summer rainfall is unpredictable and usually insufficient to meet crop water requirements. The impact of water availability on yield potential of fodder beet (Beta vulgaris L.) is unknown. A single year, single site replicated field experiment investigating biomass production, water use (WU) and water use efficiency (WUE) was carried out on a deep Templeton silt loam soil at Lincoln in 2013. The experiment had four water treatments: 1: Rain fed control, 2: Full potential evapotranspiration (ETo) replaced weekly, 3: 50% of ETo replaced every 3 weeks and 4: 50% of ETo replaced weekly. Final dry matter (DM) yield differed with treatments, increasing from an average of 24 t/ha for the rain fed crops and those receiving 50% of ETo weekly to 28 t/ha for the full ETo replacement crops and those receiving 50% of ETo once every 3 weeks. Water use more than doubled with full irrigation compared with the rain fed crops (774 vs 316 mm). The WU for the intermediate crops was 483 mm. However, DM yield was higher for the treatment with 50% of ETo replaced every 3 weeks rather than weekly. Water use was related to DM yield and accounted for the observed variation (R2=0.75) in final yield. The WUE decreased with water supply, from 80 kg DM/ha/mm for the rain fed crops to 46 kg DM/ha/mm for the full ETo replacement treatments, and 64 and 57 kg DM/ha/mm for the 50% of ETo replaced weekly and every 3 weeks, respectively. Similar DM yield and marginal WUE for the full ETo treatments and those receiving 50% of ETo replaced every 3 weeks, meant that the most economic WUE was 57 kg DM/ha/mm. Although these results are from a single and site, they suggest that full ETo replacement was uneconomic in this type of soil and therefore partial irrigation to 50% of ETo replaced every 3 weeks may be the optimum for this type of soil. It is recommended to investigate similar treatments on shallow and stony soils. Keywords: Beta vulgaris L., evapotranspiration, water use, water use efficiency, water extraction pattern, water extraction depth.