Polyhalite (PH) is a hydrated sulfate evaporite mineral containing potassium, calcium, magnesium, and sulfur, nutrients all required in significant quantities by crops, but has limited evaluation as a fertilizer for potato (Solanum tuberosum L.). Fertilizer source and application rate field trials were conducted to evaluate PH as a fertilizer for potato production in the weathered tropical soils in Brazil. We selected two locations in the potato producing region of Southeast Brazil in 2015–16, one trial was conducted during the wet season at Tapira in São Paulo and the other during the winter season at Casa Branca in Minas Gerais. A common blend, 4–14–8, was made with either muriate of potash (MOP), sulfate of potash (SOP), or PH as the K source; with kieserite and gypsum added to the SOP to make a synthetic PH with similar composition; P either as single super phosphate (SSP) for the MOP blend or mono ammonium phosphate (MAP) for the PH and SOP blends; and N as urea adjusted for the N in MAP. All blends were applied at four application rates of 62, 125, 187, and 249 kg K/ha. A control was also included consisting of N and P as urea and MAP but no K, Ca, Mg, or S. Total and marketable yields as well as potato quality including dry matter, starch, soluble solids, hardness, and crunchiness were measured at harvest using standard techniques. At Tapira, potato yields increased linearly with increasing K application rate from 22.4 t·ha−1 for the control to the highest yield of 29.2 t·ha−1 and were higher for PH and SOP than MOP (28.8, 29.2, and 25.3 t·ha−1, respectively). At Casa Branca, yields increased from 31.5 t·ha−1 for the control to 42.4 kg·ha−1 at the 62 kg K/ha application rate with no further increases at higher rates and no differences among fertilizer blends at any application rate. Polyhalite blend increased dry matter and starch at the higher application rates compared with MOP and SOP at Tapira and increased potato hardness and crunchiness at the optimum 62 kg K/ha application rate at Casa Branca. Yield response was similar for PH and SOP but quality differences between these two fertilizer blends were observed even though they were similar in composition. Differences between PH and MOP may be related either to Cl or lack of Mg in the MOP blend. PH performed well as a fertilizer for potatoes as it produced equal or higher yields and provided benefits to potato quality when compared with MOP or SOP as a K source in a common fertilizer blend.
The objective of this study was to investigate the effects of the application of indole-3-butyric acid (IBA) at concentrations of 0, 30, 60, and 90 mg·L−1, for 24 hours, on rooting of softwood and semihardwood cuttings of tea (Camellia sinensis var. sinensis ‘Yabukita’ and C. sinensis var. assamica ‘IAC-259’) collected in winter and summer. In the summer, IBA increased root percentage of softwood cuttings from ‘Yabukita’ compared with the control. However, the rooting of semihardwood cuttings was unaffected by this growth regulator. In winter, application of 90 mg·L−1 IBA increased the rooting regardless of the type of ‘Yabukita’ cuttings. In addition, in ‘IAC-259’, there was an increase in dry weight, number of roots (NOR), and rooting percentage of softwood cuttings collected in summer with application of 90 mg·L−1 IBA compared with control. In contrast, during the same period of the year, the semihardwood cuttings of ‘IAC-259’ were unaffected by the IBA. In winter, the percentage of cutting survival, rooting, the number, and length of roots were unaffected by IBA in ‘IAC-259’. Overall, we would recommend the use of exogenous IBA for rooting of cuttings collected in the summer or winter.