Effects of cropping, nutrition and water supply on accumulation and distribution of biomass and nutrients for apple trees on'M9'root systems

The effects of cropping, nutrition and water supply on accumulation and distribution of biomass and nutrients for apple trees on'M9'root systems were examined using trees growing in lysimeters. For 3-year-old 'Golden Delicious' trees, cropping significantly increased total biomass, although leaf and root biomass were reduced. For 3-year-old'Golden Delicious', 'Coxs Orange' and 'Gloster' trees, cropping only in the third year reduced root biomass by 39 to 45%. Cropping did not affect water use by trees of any cultivar early in the season, but increased water use later in the season for 'Gloster' trees. For trees with fruit, total non-structural carbohydrate (TNC) contents at the end of the season were highest in fruit (up to 1 400 g plant ^?1). For trees without fruit, TNC contents were generally highest in the roots (up to 110 g planr ^?1). Supplying trees with nutrient solution diluted to 10% of the standard composition increased the root biomass for 'Golden Delicious' trees only, but decreased biomass of above-ground tissues for all cultivars. Reducing the nutrient supply decreased water and nutrient uptake, and reduced nutrient contents within vegetative parts of the tree more than within roots. For 'Golden Delicious' trees, restricting the water supply to 50% or 25% of that consumed by control trees significantly reduced above-ground biomass, but root biomass was not significantly affected. The N, P and K. contents for the trees were also reduced by water stress, due to reduced contents within above-ground organs. Water stress reduced the TNC and starch contents of all tissues, except the roots. These results are discussed in relation to the efficiency of root systems for water and nutrient uptake.