Potassium and Phosphorus

Abstract

The response of 2 rice (Oryza sativa L., Indica) varieties to several soil applied compounds was investigated. The 2 varieties, ‘Khao Dawk Mali 105’ (KDM) and ‘Muey Nawng 62M’ (MN) have been shown to exhibit high and low, respectively, P concentrations when grown on similar soils. Plants were grown in pots filled with an Andosol or sand‐clay mixture containing P compounds and other nutrients. Japonica rice, cv. ‘Nihonbare’ (NB) was also used for a comparison.

The differences in root efficiency for P absorption among these rice varieties were estimated using the method of Hunt (7).

Root development was considerably faster in KDM than in MN under fairly low available P, ‐Ca(H₂PO₄)₂ in Andosol‐, resulting in significant differences in P absorption and in growth. Under extremely low available P, ‐AIPO₄ in Andosol‐, KDM root per unit length had a significant higher efficiency in extracting P from soil than MM. NB root² (per unit length) had a considerably greater efficiency in absorbing P as compared with KDM and MN under relatively high available P in sand‐clay mixture.

Phosphates of Fe‐ and Al‐phytates in Andosol soil were almost unavailable for all varieties, especially MN.

Key words:

• Rice varieties
• P absorption
• root development
• root efficiency