THE GROWTH RESPONSE OF SUGAR BEET TO 



SIMILAR IRRIGATION CYCLES UNDER 



DIFFERENT WEATHER CONDITIONS 



B. Orchard 

 Rothamsted Experimental Station, Harpenden, Herts. 



INTRODUCTION 



Owen and Watson (1956) reported that when prolonged drought was 

 broken by hght rainfall, unirrigated sugar beet had a greater relative growth 

 rate than irrigated controls and Gates (1955) reported a similar phenomenon 

 in young tomato plants growing in pots. Tliis paper describes an attempt 

 to reproduce and analyse these effects by controlled watering of small field 

 plots protected from rainfall by a static Dutch-hght structure. Three similar 

 experiments (two in summer and one in autumn) were done on the same 

 variety of sugar beet growing on the same plots in three successive years so 

 the effects of radiation and other weather factors on the development of 

 the drought response and the recovery from it can be considered. 



EXPERIMENTAL 



General 



Two treatments in which irrigation was withheld for a period, brief 

 drought (B) and continued drought (C) were compared with a freely 

 available moisture treatment (A). Before the drought and throughout 

 treatment A the plots were maintained near field capacity by frequent 

 watering. The plots were on a heavy clay loam, formerly a garden. The 

 moisture content- pF relationship was determined by the method of 

 Monteith and Owen (1958). Field capacity was about 28-30% of the oven 

 dry weight and the permanent wilting percentage (pF 4-2) I3"8%. The 

 moisture content at pF 4-2 was greater than for a typical Rothamsted soil, 

 possibly because of residual salts from tap-water used in previous irrigation 

 experiments. 



Sugar beet seed (Sharpe's Klein E) was washed for two hours in aerated 

 running water, planted in soil blocks and covered with sand containing 

 'Harvesan' (120 mg per kg). One seedling per block was retained, and when 

 the seedhngs were well estabUshed the blocks were planted at a spacing of 

 I ft X I ft in plots of 14 ft X 9 ft. The soil was dry at planting and afterwards 



