Response of Khao Dawk Mali 105 rice to magnesium in different paddy soils in Northeast of Thailand

Abstract

A study was carried out on the response of Khao Dawk Mali 105 rice (KDML 105 rice) in different paddy soils consisting of Phimail soil series, Roi Et soil series and Roi Et soil series, saline variant (Re-Sa) to varying rates of Mg applied at 0, 1.5, 3, 6 and 12 kg/rai.  Besides, soil extractant methods for the assessment of Mg content available to rice were compared.  Results revealed that applications of Mg had no statistically effect on rice growth and yield components, but they had a tendency to increase rice grain and stover yields except in the case of Re-Sa soil.  Magnesium applied at all rates significantly increased filled grain number of rice grown in Re1 soil (86.6-88.6%) with the exception at the rate of 6 kg Mg/rai.  Moreover, Mg application significantly decreased plant nutrient concentration and uptake in rice, except for P and Mg that the result showed the opposite trend. Soil Mg was in a residual form in mineral composition (260-333 mg/kg), while the extracted Mg varied among the extractants as follows, NH₄OAC > CaCl₂ > Mehlich III > distilled water.  Flooding the soils for 1 month clearly decreased the contents of extracted Mg but increased the total Mg as the Mg reservoir.  Soil Mg showed no positive statistical correlation with relative rice yield components.  The CaCl₂ extractant gave Mg content in soils (r=0.776**) and in flooded soils (r=0.748**) identical correlated with Mg concentration in rice husk and bran.  In addition, the extracted Mg in flooded soils by distilled water (r=0.742**) and CaCl₂ (r=0.827**) similarly had a significant correlation with Mg concentration in rice grain.  Both extractants can therefore be used to estimate Mg availability for rice in these soils.