Effects of fertigation of the black currant cultivar "Ben Tron" (Ribes nigrum l.)

The Scottish black currant cultivar "Ben Tron" (ND12/26 x ((Vistavotnjaja x (Mendip Cross x R. dikuscha) x (Goliath x Ojebyn)) x Westra) is high-yield ing with an erect growth habit, good fruit quality and complete field resis tance to mildew (Sphaeroteca mors-uvae) when grown in Norway. A fertilizer experiment with different rates of N, P and K, methods and timing of fertil izing was established at Apelsvoll Research Centre Division Kise, Norway (6 0 degrees 40` N; 10 degrees 11' E) in 1991. Records of yield, berry and clu ster size, soluble solids and concentration of N, P and K in leaf dry matte r were collected over 5 seasons. The experimental field was fitted with a p ressure compensated trickle irrigating system with an emitter spacing of 50 cm and a capacity of 1.6 l/h. The field was irrigated whenever the water d eficit exceeded 10 mm. The plots were either fertigated, broadcast fertiliz ed or a combination of the two methods was used. Broadcasting was performed either in early spring or in autumn, while fertigation was carried out fro m the last week of May until early August. The bushes were planted with a s pacing of 1.5 m in rows 4.0 m apart. Grass that was kept short covered the alleyways, combined with a herbicide strip 1.0 m wide in the rows. All fert ilizer was applied only to the herbicide strip, and only 25 % of the total area was therefore fertilized. Fertigation affected yield significantly in all years. Using a low rate of fertilization (N=12.5 kg/ha, P=3.3 kg/ha, K= 10.0 kg/ha) the average yield was 38 % higher in fertigated plots compared to plots given the same amount of fertilizer broadcast in early spring. A l ow rate of fertilization broadcast in autumn also gave a greater yield than fertilizing in spring. When the plots were fertilized at a medium rate of fertilization (N=25.0 kg/ha, P=6.6 kg/ha, K=20.0 kg/ha), the highest yield was obtained after a combination of fertigating and broadcasting in autumn. The greatest yield was, however, obtained using the highest rate of fertil ization (N=37.5 kg/ha, P=9.9 kg/ha, K=30.0 kg/ha) by a combination of broad casting in early spring, fertigation and broadcasting in autumn. The effect s on berry size by different rates and methods of fertilization corresponde d closely with the effects on yield. The content of soluble solids in the b erries was little affected by the different rates and methods of fertilizat ion. Fertigation gave a higher DM concentration of N in the leaves than bro adcasting at both low and medium rates.