|dc.description.abstract||Fodder beet (Beta vulgaris L. subsp. vulgaris var. Alba) is commonly grown in New Zealand as a forage crop to feed dairy cattle. It has high potential yields and feed quality advantage over other traditional winter crops e.g. kale (Brassica oleracea) and swedes (Brassica napobrassica). For these reasons, farmers, agronomists, crop modelers and breeders have heightened their interest in this crop. However there has been increased concern about how nutrients and water are used to meet potential yield expectations in New Zealand. The rationale of this research is that different rates nitrogen and water availability will lead to differences in crop growth and development in the field and potentially final crop yield. The hypothesis is that if water and nitrogen are important sources of crop yield variation, they must influence yield components that include, cumulative radiation interception by the crop (Rcum), radiation use efficiency (RUE) and fraction of total dry matter partitioned in the root (froot). A field experiment was conducted at Plant and Food Research Ltd at Lincoln, Canterbury, New Zealand, to investigate the influence of water and nitrogen on fodder beet growth and development and quantify their impact on yield. There were three nitrogen (0, 30 and 300 N ha-1) and two water (zero and at field capacity) treatments.
Water was the main factor limiting crop yield as there was 98% higher dry matter in the irrigated treatment (28.31 t ha-1 DM) compared with the dry treatment (14.31 t ha-1 DM). Overall, 55% of this yield difference was explained by greater cumulative radiation interception. The irrigated treatment increased RUE by 27% (1.47 g DM MJ-1) compared with dry treatment (1.16 g DM MJ-1). The fraction of total dry matter partitioned in the root (froot) was 5.4% greater in the dry treatment (85.0%) compared with the irrigated treatment (79.6%). The 300 N dry treatment increased total dry matter production by 25% compared with the control nitrogen treatment (0 N). This was mostly explained by 42% greater radiation interception and 1.2% higher froot. The irrigated 50 N and 300 N nitrogen treatments, increased dry matter production by 18% and 23%, respectively, compared with the control treatment. The yield increase from the N treatments was also explained by the larger amount of radiation intercepted by the crop at the end of the season. This was 14% and 42% higher for the 50 N and 300 N treatments, respectively, compared with the control treatment. Froot decreased by 8.3% in 300 N compared with the control, but 50 N had no effect. There was no significant difference in yield between the 50 N and 300 N treatments. A possible reason for this is that 300 N had reached 95% maximum yield 9 DAP or 102 oCd before 50 N. After this point, light intercepted did not result in net photosynthesis and growth ceased earlier. Leaf chlorophyll concentration was 30% higher in water stressed plants. The dry 300 N and irrigated 300 N increased leaf chlorophyll by 10.3% and 13.8%, respectively, compared with the control. Greater leaf chlorophyll concentration did not seem to benefit total yield, as RUE was unaffected by nitrogen and decreased under water stress.
The results confirm the importance of nitrogen and water availability for crop radiation interception and consequently yield. In addition, RUE was significantly lower under limiting water availability. Froot was lower in both limiting water and nitrogen conditions whilst under irrigation. Froot increased under dry conditions and high rates of N. These findings can be used to develop a fodder beet simulation in model to optimize crop yield, nitrogen and water use. These results could also influence the priority of traits selected for during the plant breeding process of new cultivars with the aim of improving yield.||en