The response of'Starking Delicious' (Malus domestica Borkh.) apple trees to four N fertigation treatments in drip irrigation (50, 150, 250 and 400 kg N ha-l, supplemented with a uniform dose of 400 kg K ha-l ) was investigated in a field experiment during 6 years.Nitrate nitrogen in the soil was proportional (7-58 mg kg -1) to the applied N dose at the end of a 6 week fertigation period in the spring. At other times, the nitrate concentration in the soil was very low. Soil K decreased with depth and in the 0-30 cm soil layer it was negatively correlated with the applied N dose, before fertigation started. At the end of the spring fertigation period, higher K was found in all soil layers analyzed.Vegetative growth was correlated positively with the amount of N applied. Leaf chlorophyll and N were significantly lower only in the lowest N treatment, while increased fruit size and decreased fruit color were measured only in the higher N treatments. Yield was severely biennial. In the 'On' years crop load was heavier as less N was applied. An extremely high crop load in the lowest N treatment was followed by a reduced flower density and yield in the following season. In the 'Off years, a significantly higher yield was obtained with the 150 kg ha-~ dose. The dry weights, N, P and K contents of the above ground parts of mature apple trees were determined.
Meager information is available on the specific effects of root volume (V) and N concentration in the water (CN) on uptake rates of water and N by apple trees, as related to fruit yield and tree growth. To investigate this relationship, Golden Delicious/Hashabi trees were grown for 5 years in containers of 200, 50 and 101. Trees in the 200-1 containers were irrigated with a nutrient solution containing 10.7 + 1.3, 7.1 + 1.5 or 2.5 _ 1.0 mM NO 3 . Trees in the remaining two container-volume treatments were uniformly supplied with a solution of 7.1 + 1.5 mM NO 3 . Elevated CN had no effect on the rate of water uptake, but increased the rate of N absorption by the trees from 2.4 to 4.8 g N tree-~ day-~ during July. The stimulated N uptake rate stemmed from enhanced fluxes of N uptake by the roots. CN had a negligible effect on root weight and root permeability to NO 3 and water. The elevated N uptake rate did not result in greater fruit yield and growth, or greater N content in tree organs, indicating considerable release of N from living and decaying roots to the growth medium. Reducing the container volume decreased yield, total dry matter production and N and water uptake rates, but increased root permeability to NO3 and water, and total soluble solids in fruits. The all-season average CN in the irrigation solution above which N concentration in the transpiration stream was lower than the inflowing CN was 4.2 mM NO 3.
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