Response by sugar beet to irrigation, 1965–75

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Abstract
Summary: Sugar yield increases from irrigation in 19 experiments on a sandy-loam soil at Broom's Barn over an 11-year period were examined in relation to rainfall and to both potential and measured soil moisture deficit. Irrigation increased average yield from 7·6 to 8·3 t sugar/ha and in six of the years significantly increased yield by more than 1 t sugar/ha (15%). The experiments also tested plant density, nitrogen, harvest date and time and amount of irrigation. Without irrigation, maximum sugar yield was from a density of 74000 plants/ha but larger densities gave slightly more yield when irrigated. Irrigation affected the magnitude of response to nitrogen but 100 kg N/ha gave the most profitable yield increase, both with and without irrigation. Yield increases of about 1 t sugar/ha (15%) between early and late harvesting were also independent of irrigation. Early irrigation of 25 mm and 50 mm in June and July respectively increased yield in 4 of the 5 years but in all years applications in late summer did not increase sugar yield. The main factors controlling the yield response to irrigation were period and size of deficit. The soil type and summer rainfall at Broom's Barn were compared with those in 36 other experiments at five localities between 1947 and 1973; yield increases at Broom's Barn were smaller, probably because the others were on lighter soils.