Walnut in Sweden: effects of nurse trees, weed control and fertilization on five-year survival and growth of planted Juglans × intermedia NG23 and NG38

Abstract

ABSTRACT This study quantified the effects of different establishment practices on survival, dieback and early growth of Juglans × intermedia NG23 and NG38 planted in a statistically designed field experiment on glacial till in southern Sweden. Establishment practices included the use or absence of nurse trees (Populus maximowiczii × trichocarpa var. OP42 planted one year before J. × intermedia), weed control (2 m2·tree−1) and fertilization (+25 g N·tree−1·year−1). NG23 transplants were smaller than NG38 at the time of planting. The overall survival rate was 97%. NG23 suffered marginally more mortality than NG38. Leader shoot dieback occurred in all treatment combinations but was most severe in the presence of nurse trees. NG23 suffered less dieback than NG38. Annual height growth of trees unaffected by dieback increased with increasing levels of precipitation during the growing season (194–407 mm) and with increasing soil quality in terms of nitrogen (94·10−3–607·10−3 g·g−1), base saturation (14–99%) or available soil water capacity (8.6–30.6 l·m−3). It was negatively influenced by poplar nurse trees and positively by fertilization. Weed control had no impact on height growth, possibly due to inefficient implementation. With nurse trees, NG23 had stronger growth than NG38. The opposite was true without nurse trees. It was hypothesized that less growth and more dieback resulted from competition for water.