Abstract
ABSTRACT Potassium (K) is an essential nutrient for upland rice growth, but little information on the effects of K on root growth and nutrient uptake capacity of upland rice is found. Therefore, an experiment was conducted under greenhouse conditions to evaluate the influence of soil K levels on root growth and nutrient uptake of four upland rice cultivars. A completely randomized experimental design, in a 4x4 factorial scheme (4 levels of K: 20, 40, 80, and 160 mg dm-3; 4 cultivars: Caiapó, BRS-Primavera, IAC-202, and Maravilha) was used, with four replications. Based on regression equations, the highest values of root length density would be found with 136 mg dm-3 of K. The root diameter and dry matter, shoot dry matter and shoot K concentration increased linearly with the increasing K rates. The shoot K concentration of the upland rice cultivars did not differ. The increased level of K in the soil reduced the shoot Ca concentration of intermediate and modern cultivars, and the shoot Mg concentration of all cultivars. The potassium fertilization increased the plant growth, but the magnitude of this effect varied according to the cultivar.
Highlights
Rice (Oryza sativa L.) is grown in Brazil using two different cropping systems, upland and lowland (SANTOS; STONE; VIEIRA, 2006)
The main role of K in plants is the osmoregulation of cells and tissues (FAGERIA; BALIGAR; JONES, 2011a), the increase in rice grain yield due to K fertilization is not as significant as the increases due to nitrogen and phosphorus fertilization, even considering the variations among cultivars (FARINELLI et al, 2004)
The characteristics of the upland rice root system may be an important factor to increase the K fertilization effect on grain yield, but little is known about their mechanisms
Summary
Rice (Oryza sativa L.) is grown in Brazil using two different cropping systems, upland and lowland (SANTOS; STONE; VIEIRA, 2006). The plant yield capacity is reduced under upland conditions, mainly due to water stress, inadequate application of nutrients has been reported as an important limiting factor of plant growth (CLOVER; MALLARINO, 2013; LOPES et al, 2013). The main role of K in plants is the osmoregulation of cells and tissues (FAGERIA; BALIGAR; JONES, 2011a), the increase in rice grain yield due to K fertilization is not as significant as the increases due to nitrogen and phosphorus fertilization, even considering the variations among cultivars (FARINELLI et al, 2004). The characteristics of the upland rice root system may be an important factor to increase the K fertilization effect on grain yield, but little is known about their mechanisms. Root systems can develop significantly to uptake water and nutrients, even under low K availability (FAGERIA; BALIGAR; LI, 2008; GUIMARÃES et al, 2011). The pattern of root growth is controlled genetically, the soil chemical properties can modify the root architecture (SAINJU et al, 2005). Zobel (2003) confirmed that the root length density is usually affected by both factors (genotype and soil conditions), but the root diameter is more influenced by soil conditions
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