Abstract
Salinity levels in soils of the Outer Coastal Plain of Rio Grande do Sul, Brazil, can be high, due to excess of Na in the irrigation water, evapotranspiration and soil development from marine sediments. The cultivation of irrigated rice could be an alternative, since ion uptake as well as leaching by the establishment of a water layer could mitigate the effects of soil salinity. This study aimed to evaluate the dynamics of basic cations in the solution of Albaqualf soils with different salinity levels growing irrigated rice. The plow layer contained exchangeable Na percentages (ESP) of 5.6, 9.0, 21.2 and 32.7 %. The plant stand, dry matter, Na, K and Ca + Mg uptake at full flowering and grain yield were evaluated. The levels of Na, K, Ca + Mg and electrical conductivity (EC) in the soil solution were also measured weekly during the rice cycle at four soil depths, in the water layer and irrigation water. The Na, K and Ca + Mg uptake by rice at full flowering was used to estimate ion depletion from the layer under root influence. Soil salinity induced a reduction in the rice stand, especially in the soil with ESP of 32.7 %, resulting in lower cation uptake and very low yield at that site. As observed in the water layer and irrigation water, the Na, K, Ca + Mg and EC levels in the soil solution decreased with time at depths of 5, 10 and 20 cm, regardless of the original soil salinity, showing that cation dynamics in the plow layer was determined by leaching and root uptake, rather than by the effect of evapoconcentration of basic cations in the soil surface layer.
Highlights
In Rio Grande do Sul, Brazil, rice is grown in six different regions in the Southern half of the State, called Fronteira Oeste, Campanha, Depressão Central, zona Sul and Planícies Costeiras Interna and Externa
This study aimed to monitor the influence of irrigated rice cultivation on the dynamics of basic cations and electrical conductivity in soils with different salinity levels in the Outer Coastal Plain of Rio Grande do Sul, Brazil
To observations related to the establishment, much less dry matter was produced in Sinval than at the other locations (Table 3), in response to the higher soil salinity (Table 1)
Summary
In Rio Grande do Sul, Brazil, rice is grown in six different regions in the Southern half of the State, called Fronteira Oeste, Campanha, Depressão Central, zona Sul and Planícies Costeiras Interna and Externa (here Outer and Inner Coastal Plain). The discrepancies observed between some regions may be attributed to the different soil types (Streck et al, 2008), variation in solar radiation (Mota, 1995; Custódio, 2007) and region-specific stress, such as soil and water salinity. In this context, the lagoon Laguna dos Patos is highly important, because of its connection to the Atlantic Ocean. The soils can be threatened by salt deposition at incompatible levels for rice cultivation
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