Abstract
Abstract: The objective of this work was to evaluate the yield performance and foliar nutrient contents of blackberry (Rubus sp.) cultivars in response to the increase in potassium fertilization. The experiment was carried out in a soil with pH 5.2 and 22 mg dm-3 K content in the fourth and fifth years of production of the Brazos, Guarani, BRS Tupy, and BRS Xavante cultivars, grown in the state of Minas Gerais, Brazil. The tested K2O rates were distributed in a 4x4 factorial arrangement, which consisted of four rates of K2O per plant (10, 20, 30, and 40 g) and of the four blackberry cultivars, distributed in four randomized complete block designs. The maximum economic efficiency (MEE) yield, the formation of primocanes, and the critical level of foliar nutrients were evaluated. The K fertilization recommended for blackberry cultivation in Brazilian conditions is not sufficient to maintain foliar nutrient contents at an adequate level. Fertilization with 20 g per plant per year of K2O, twice the recommended amount, favors the MEE yield, compatible with the yield performance of the cultivars. Foliar nutrient contents should be evaluated to recommend the proper fertilization for the orchard to reach its maximum yield potential.
Highlights
The use of fertilization rates recommended in other countries in Brazilian conditions creates problems for the blackberry (Rubus sp.) production system, such as a slow or excessive plant development, susceptibility to pests and diseases, and a low yield and fruit quality (Pereira et al, 2015a)
The K rates applied to the soil increased blackberry yield in the two evaluated cycles (Table 1)
The average rates of 30 and 20 g K2O obtained for the maximum technical efficiency (MTE) and maximum economic efficiency (MEE) yields, respectively, are higher than that recommended for soils with a low K content of 10 g per plant (Manual..., 2016)
Summary
The use of fertilization rates recommended in other countries in Brazilian conditions creates problems for the blackberry (Rubus sp.) production system, such as a slow or excessive plant development, susceptibility to pests and diseases, and a low yield and fruit quality (Pereira et al, 2015a). Information on blackberry fertilization needs to be improved based on the response of different cultivars in Brazilian regions, considering foliar nutrient contents and plant yield. Depending on the nutrient content of the soil, the recommended potassium rates for orchard maintenance range from 0 to 66.7 kg ha-1 K2O (Manual..., 2016). In countries that consider soil and primocane K contents, the applied amount may be as high as 112 kg ha-1 K2O (Hart et al, 2006). High quantities of the nutrient have been applied to blackberry in high-yield situations, especially since K can induce growth, increase yield, and influence fruit firmness when nitrogen is not limiting (Pereira et al, 2015b)
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