Properties of Paddy Soils Affected by Algal Boom or Unsuitable Irrigation Water

Abstract

    In this study, the chemical properties of two paddy soils located in a Central Region were determined.
The goal was to better understand why abnormal rice growth occurred in this Thai region and to find possible practical solutions to tackle this problem for next rice production crop cycles. A blooming of algae prohibited rice growth and tilling in the first field, which was located in Hun Kha district, Chai Nat province. In the second field, located in Sao Hai district, Saraburi province, poor germination and growth of rice occurred during the drought season every year, especially in areas where numerous white particles can be found on the soil surface. Soil samples from the first field were collected to measure soil pH, EC, OM, total-N, total and Mehlich III-extractable concentrations of P, K, Ca, Mg, Cu, Zn, Mn, and Fe. Soil samples from the second field as well as a water sample from it, or its irrigation canal, were collected to determine pH, EC, total and water soluble concentrations of Na, K, Ca, Mg, and Fe. Results showed that the chemical properties of soils were favorable for algae growth in the first field, i.e. high pH (above 7), EC lower than 1.2 dS/m, high amount of OM (>5%), N (ammonium form), Mehlich-III extractable P and Fe contents. In the second field, soil pH ranged from 4.11 to 6.35, while ECs and SAR were lower than 2 and 13 dS/m, respectively. Therefore, it could not be considered as a salt-affected soil. High amounts of Na (990 mg/L) and Ca (1,129 mg/L) were found in the water collected from the irrigation canal. The EC and total dissolved solids in this water was up to 7.35 dS/m and 3,558 mg/L, respectively. Thus, the water from this canal was considered as unsuitable to irrigate agriculture fields and could be a main cause of abnormal rice growth in the second field.