CARACTERÍSTICAS PRODUTIVAS, MORFOFISIOLÓGICAS E SANITÁRIAS DE CULTIVARES FORRAGEIRAS ADUBADAS COM POTÁSSIO

Abstract

The objective was to evaluate the effect of different doses of potassium (K) on productive, morphogenic, physiological characteristics and on the incidence of diseases in different forages. Fifteen cultivars separated by gender were evaluated and evaluated in two different experiments carried out in a greenhouse. Experiment 1 was carried out in a randomized block design in a 6x4 factorial scheme, with the cultivars of Panicum: Tanzania, BRS Kenya, Mombasa, BRS Zuri, Massai, BRS Tamani and four doses of K: 0, 205, 410 and 820 mg dm -3. Experiment 2 was a 9x4 factorial, composed of Brachiaria cultivars: Xaraés, BRS Piatã, Marandu, BRS Paiaguás, BRS Ipyporã, Basilisk, Comum, Tupi and Ruziziensis, and four doses of K: 0, 205, 410 and 820 mg dm -3. The first cut took place 50 days after sowing and the other cuts to quantify forage production were performed every 28 days during five regrowth cycles; morphogenesis and SPAD chlorophyll were measured weekly and tiller numbers were counted before each cut. The collection of physiological parameters (photosynthesis, stomatal conductance, transpiration, leaf temperature and CO2) were performed using an IRGA® type canopy analyzer every 28 days. After the last cut, the roots were sieved, dried and weighed to determine the mass (g pot-1). The severities of brown spot, bipolaris leaf spot and mosaic virus were also evaluated. The results show that at the highest rate of K evaluated, the highest rates of leaf appearance and the highest rate of stem elongation were observed in the Tupi cultivar, and the highest phyllochron in the Ruziziensis cultivar, and at the highest K dose there was no difference between the cultivars for the TSeF. Higher number of tillers were recorded in cultivars Comum and Tupi. In the absence of fertilization and at doses of 205 and 410 mg dm-3 of K higher DPP were observed in cv. Tupi and the largest forage production. Increasing doses of K were responsible for increasing linear responses in leaf photosynthesis and stomatal conductance in Tanzania, Kenya, Mombasa, Zuri, Massai and Tamani cvs. On the other hand, transpiration and leaf temperature revealed a positive linear response to the inclusion of K in all cultivars. Chlorophyll was fitted to a quadratic regression model, with maximum production estimated at the dose of 106.00 mg dm-3 of K with 35 SPAD units. In the absence of fertilization and at the lowest K dose, the highest severities caused by brown spot and bipolar spot were recorded in all cultivars. However, higher doses of K increased the severity of mosaic virus in all cultivars in both experiments. Potassium fertilization in tropical forages guarantees an increase in morphogenic variables, in the number of leaves and tillers, increases photosynthesis and stomatal conductance, parameters that notably affected forage production and ensured faster plant growth. In addition to providing greater resistance to brown spot, and lower levels of severity caused by the mosaic virus