Yield Component Responses of ‘Hull Thornless’ Blackberry to Nitrogen and Mulch

Abstract

Abstract The response of ‘Hull Thornless’ blackberry (Rubus spp.) to annual applications of three N rates (0, 41, and 123 kg N/ha) and straw or wood chip mulch plus 41 kg N/ha was studied. Pruning weight per plant increased linearly with increasing N rate in 1986 and 1987 and with straw mulch in 1987. Plants mulched with wood chips had the largest mean cane cross-sectional area, while neither N rate or straw mulch had an affect. Number of lateral branches per cane was not affected by any treatment. Yield increased linearly with N rate. Plants that received straw mulch produced yields that were greater than or equal to the high N rate. Mean fruit weight increased in response to straw mulch and increasing N levels in 1986, but only to the straw mulch in 1987. The number of flowers per cane and per inflorescence increased with increasing N rate, but inflorescence number per cane and fruit set were not affected. As N rates increased, yield per square centimeter of cane basal cross-sectional area increased. Both mulches decreased inflorescence number per square centimeter of cane basal cross-sectional area, but did not influence any other components of yield. Mean cane cross-sectional area, lateral branches per cane, inflorescences per cane, flowers per inflorescence, and mean fruit weight were significantly and positively correlated with yield per plant in 1987. Averaged over years, as the fertilizer N rate increased, primocane foliar N content increased, P declined, and K, Ca, Mg, and Mn were not affected. Mulching had no effect on nutrient element content.