ABSTRACT Little is known about the management of high-yield clonal Coffea canephora in the Amazonian Region, mainly for nutritional aspects and cultivation system efficiency. This study aimed to evaluate the influence of different nitrogen and potassium fertilization rates on coffee grain yield and fertilizer use efficiency of C. canephora trees. An experiment was performed at an experimental field of the Embrapa Rondônia in Porto Velho (RO), Brazil. It was carried out in a split-plot scheme with six doses of 20-00-20 NPK formulation (0; 250; 500; 1,000; 2,000; and 3,000 kg ha-1) and three years of evaluation (2014, 2015, and 2016). An interaction between fertilizer dose and crop year was observed. Fertilizer doses showed an exponential behavior, with maximum yields of 51, 114, and 79 bags ha-1 at 3,000 kg ha-1 in the crop years of 2014, 2015, and 2016, respectively. Such a behavior impacted average and accumulated yields in the three harvest seasons. As for crop year effect within each fertilizer dose, the highest yield was reached in the second harvest after pruning for renewal of orthotropic stems. Moreover, fertilizer use efficiency by plants decreased exponentially, with the highest value at the lowest dose. Increasing doses of 20-00-20 formulation promoted an exponential increase in grain yield but decreased its use efficiency by C. canephora plants. This management also stimulated a strong biannual production.

ABSTRACT This study was conducted with the objective of evaluating the quantum yield, photosynthetic pigments and biomass accumulation of mini watermelon cv. Sugar Baby, under strategies of irrigation with saline water and potassium fertilization. The experiment was conducted in a randomized block design, in a 8 × 3 factorial scheme, with three replicates, corresponding to eight strategies of irrigation with saline water applied at different phenological stages of the crop (control - irrigation with low-salinity water throughout the crop cycle, and salt stress in the vegetative, vegetative/flowering, flowering, flowering/fruiting, fruiting, fruiting/ fruit maturation and fruit maturation stage) and three potassium doses (50, 100 and 150% of the recommendation). The dose of 100% corresponded to 150 mg of K2O kg-1 of soil. Two levels of electrical conductivity of water were used: 0.8 and 4.0 dS m-1. Irrigation with water of 4.0 dS m-1 continuously in the vegetative and flowering stages increased the initial fluorescence and decreased the quantum efficiency of photosystem II of mini watermelon fertilized with 100 and 150% of K recommendation. Fertilization with 50% recommendation did not interfere in the fluorescence parameters of the mini watermelon, regardless of the irrigation management strategy. Chlorophyll a synthesis is inhibited by salt stress in the vegetative/flowering, flowering, flowering/fruiting, fruiting/maturation stages, as well as for total chlorophyll, except for the flowering stage. Application of 4.0 dS m-1 water in the flowering, fruiting/maturation and maturation stages promoted greater biomass accumulation in mini watermelon.