Deep phosphorus fertiliser placement and reduced irrigation methods for rice (Oryza sativa L.) combine to knock-out competition from its nemesis, barnyard grass (Echinochloa crus-galli (L.) P.Beauv)

Abstract

Productivity of rice is increasingly being constrained by limitations in the quantity, quality, and cost of water and nutrients, and competition from weeds. This is a ‘commentary’ on the recent work of Weerarathne et al. (2015). They reported new discoveries from greenhouse experiments that showed that precise deep placement of phosphorus (P) fertilizer 15 to 20 cm below ground level in low-phosphorus-containing soils irrigated using methods such as “alternating wetting and drying” that reduce water use, dramatically increased the competiveness of rice against its most widespread and costly weed pest, barnyardgrass (Echinochloa crus-galli). The growth of barnyardgrass was severely stunted because its roots did not reach the depth necessary to readily access the P fertilizer. In contrast, rice plants maintained robust growth under these conditions because they adapted by lengthening their roots and adding more fine roots, which allowed them to reach, take up, and utilize the deeply placed P.