Plant Nutrients of Rice (Oryza sativa) var. RD41, Pathum Thani1 and Khao Dawk Mali105

Abstract

The nutrient contents of 3 rice varieties: RD41, Pathum Thani1 (PTT1) and Khao Dawk Mali105 (KDML105) were determined at 6 stages: seedling, early tillering, maximum tillering, flowering, harvesting and late harvesting. All nutrient concentrations (N, P, K, Ca, Mg, Fe, Mn, Cu, Zn and B) were at their highest levels during the vegetative phase, and gradually decreased during the reproductive phase. Nutrient contents increased linearly with increased dry mass. During early stage of growth, the rapid construction of shoot required higher amounts of N and K, whereas a steady increase of P, Ca and Mg was required throughout the growing period. In the reproductive part, N was 3–5 times higher than other nutrients. Whole plant major nutrient contents in all three varieties were similar during vegetative phase, with potassium (1.2–1.8%) and N (0.9–1.8%) contents being the most abundant. The levels became different at the reproductive phase, as KDML105 continued to cumulate biomass after flowering, it required much higher amount of nutrients up to harvesting. N in the reproductive part was as high as in the vegetative shoot, while K reduced to ¼, while other nutrients were miniscule. The fertilizer ratio for RD41 was 3.5 : 1 : 1.8, as similar for PTT1 at 3.4 : 1 : 1.9, but that for KDML105 was distinctive at 2.2 : 1 : 2.1. The application of the widely recommended amount of fertilizer was estimated to barely compensate for N and P in the harvested grain, with almost or no application of K, Ca and Mg. The incomplete types and insufficient amount of nutrients applied to replenish the soil in each rice production cycle is deemed as the cause of the stagnant rice yield of the country.