Effect of nitrogen and cane density on cane architecture, fruit and fruit yield components in primocane bearing red raspberries
Wolukau, Joseph Ngwela
Nitrogen fertilization and cane density management are the most critical factors in the commercial production of red raspberries. In general, little is known about these factors in relation to primocane bearing red raspberries and their effect on fruit yield. In two separate experiments, four levels of nitrogen and four levels of cane density were investigated on 2 primocane bearing red raspberries, Rubus strigosus, selections "8008" and "8114", respectively. The experiments were conducted at three sites in Manitoba: a clay soil at St-Adolphe, a clay-loam soil at Morden, and a sandy soil at Souris. In the second year of the study (1991), only the latter two sites were used. A nitrogen response experiment was repeated in a soilless medium in a green house in 1991. Parameters investigated included number of flowers per lateral and per cane, fruit, set, fruit yield (per cane and per plot), number of fruits per lateral, fruit size, fruit dry weight, cane height, cane diameter, number of nodes per cane, internode lengths, number of laterals per cane, length of laterals and lateral branch angle. High nitrogen and row cane density had similar effects on fruit yield components: canes were larger in diameter, and the canes had more laterals which were progressively longer towards the bottom of the cane. At high cane density the relationship of lateral length from the tip to the bottom of the cane was curvilinear. The lateral branch angle increased with cane density. similarly, both high nitrogen and low cane density increased the number of laterals and the proportion of cane that fruited. High nitrogen increased cane height while row cane density decreased cane height. Nitrogen and low cane density increased the number of fruits per lateral and per cane, fruit size and fruit yield per cane. Nitrogen increased the overall fruit yield by as much as 3 times on the sandy soils but had less effect on clay-loam soils. In the cane density study, although overall fruit yield increased with increasing cane density, the increases were not significant due to the greater productivity of individual canes at row cane density. The increase in overall fruit yield stabilised at high cane density and there was a tendency for it to decrease after an optimum number of canes per meter row was reached. The application of nitrogen increased fruit yietds significantly. It can be concluded that nitrogen fertilization and cane density management could improve yield component, performance and the yield potential of primocane bearing red raspberries.