Effects of early season and autumn nitrogen applications on young ‘Keisie’ canning peach trees on a sandy, infertile soil

Abstract

The effects of autumn (A) and early season (S) nitrogen (N) applications were investigated in a young ‘Keisie’ canning peach orchard on an infertile sandy soil in the Western Cape Province, South Africa. Over the first four consistent bearing seasons, AN was supplied at four levels, averaging 19.9, 39.8, 59.9 and 119.7 g N tree⁻¹, respectively (treatments AN1, 2, 3, and 4). Early-season N was supplied at three levels, averaging 42.4 (SN1), 82.2 (SN2) and 157.0 (SN3) g N tree⁻¹. Four-year average yields tended to increase as the AN application rate increased from AN2 to AN4 (39.8 to 119.7 g N tree⁻¹), and also tended to increase with increasing SN application rate. At the lowest level of AN (19.9 g tree⁻¹) the yield and growth responses to moderate (82.2 g tree⁻¹) and high (157.0 g tree⁻¹), but not to low (42.4 g tree⁻¹) rates of SN, were large. Thus, whilst yields in AN2, AN3 and AN4 were greater by 4.6% on average in SN2 than in SN1, and by 6.8% in SN3 than SN2, the yields in AN1 were 44.6% greater in SN2 than SN1 and 1.2% greater in SN3 than in SN2. Only in SN1 were progressive yield responses observed with increasing AN. Annual increases in trunk circumference, averaged over the same period, showed the same pattern of response to AN, and to SN, as average yield. Fruit and leaf N concentrations increased with SN at all levels of AN, but fruit diameter and single fruit mass increased with SN only at the lowest level of AN. A high total N rate of 222 g tree⁻¹ (247 kg ha⁻¹), in three applications, was required for a 26.4 t ha⁻¹ yield in the seventh season on this infertile, sandy soil.