Variability of some important soil chemical properties of rainfed low land paddy fields and its effect on land suitability for rice cultivation

Abstract

Available soil-phosphorus (P), exchangeable soil-potassium (K), soil pH and soil Electrical Conductivity (EC) affect rice production and are highly variable in nature mainly due to the variability in water availability. Therefore, experiments were conducted to find out the variability of some important soil chemical properties of rainfed lowland paddy fields and their effect on land suitability for rice cultivation in the Dry (Mahananeriya), Intermediate (Ibbagamuwa) and Wet (Alawwa) regions in the Kurunegala District of Sri Lanka. Randomly collected soil samples from the above three areas were analyzed for available soil-P, exchangeable soil-K, soil pH (1:2.5) and EC (1:5). Thematic maps for each parameter were prepared using Inverse Distance Weighted interpolation technique. Weighted sum technique was used to overlay maps to prepare the suitability map as Marginally Suitable, Moderately Suitable, Suitable and Highly Suitable. Results showed that the available soil-P and EC levels are preferable for rice cultivation in the rainfed lowland paddy fields in all three regions. Even with this situation, the potential productivity of the lands cannot be obtained due to variability of soil pH and exchangeable Potassium contents. Soil pH and the exchangeable soil Potassium in all rainfed paddy areas of Alawwa is far below the optimum levels for paddy cultivation. In terms of these soil chemical properties, 42% and 32% of rainfed paddy fields in Ibbagamuwa and Mahananeriya regions, respectively, are either highly suitable or suitable but 79% land extent of the rainfed paddy in Alawwa is marginally suitable for rice cultivation. Therefore, a blanket recommendation of remedial measures cannot be introduced to improve productivity of the rainfed paddy fields in these regions while site-specific remedial measures would help to overcome the problems of specific soil chemical properties.

Basic Soil Data Requirements for Process-Based Crop Models as a Basis for Crop Diversification

“…The diversity of observed soil types is captured by global databases to some extent as some of the parameters such as pH in dry and wet zones in all three databases are significantly different. Rathnayake et al [61] reported pH ranges of 4.1 to 7.7 (1:5) and >4.1 to 5.09 (1:5), respectively, in their study areas in DZ and WZ. Although all of the datasets used in this study show ranges within the range mentioned above, failure of observed data to reflect lower pH variation in DZ shows that more local data are required before any conclusion can be made regarding soil acidity in DZ as pH value is highly sensitive to soil moisture content.…”

“…The diversity of observed soil types is captured by global databases to some extent as some of the parameters such as pH in dry and wet zones in all three databases are significantly different. Rathnayake et al [61] reported pH ranges of 4.1 to 7.7 (1:5) and Of all 9 parameters, volumetric moisture content (15 bars level) showed the lowest RMSE across all layers while CEC showed higher RMSE (Table A1). In general, interpolating soil physical properties proved to be challenging as the lowest RMSE for all three parameters belong to the Radial Basis function method which is a deterministic interpolation technique using a regularised spline method which does not use the inherent autocorrelation that exists in soil properties.…”

Variability of pH and EC of Selected Rice Cultivated Soils of Sri Lanka

“…Low soil pH values observed in the WZ (WL and WM) can be due to several reasons. Leaching of basic cations such as K, Ca and Mg is high due to heavy rainfall occurring in these zones (Liu et al, 2013;Rathnayake et al, 2015a;Indraratne 2020;Nayakekorale et al, 2020). Ultisols are the most abundant soil order in WZ, and those have a high weathering and leaching rate under warm temperatures and high soil moisture availability (Indraratne, 2020).…”

“…These conditions affect soil biological, physical and chemical properties (Najafi, 2013;Guo et al, 2018). Among the soil's chemical properties, soil pH and electrical conductivity (EC) are two important variables that widely fluctuate with soil moisture content, thus affecting the productivity of rice crop (Rathnayake et al, 2015a).…”