Tropentag 2021, September 15 - 17, hybrid conference, Germany "Towards shifting paradigms in agriculture for a healthy and sustainable future"

Nitrogen Source Affecting the Competitiveness between Lowland Rice and Weeds under Low and High Vapour Pressure Deficit

¹Vietnam National University of Agriculture (VNUA), Dept. of Cultivation Sciences, Vietnam
²University of Hohenheim, Inst. of Agric. Sci. in the Tropics (Hans-Ruthenberg-Institute), Germany

Abstract

Implementation of water-saving irrigation practices in lowland rice results in increased availability of nitrate (NO₃^-) in the soil and favours germination of upland weeds. Since plant species show a specific preference for either ammonium (NH₄⁺) or NO₃^- as nitrogen (N) source, changes in both soil NO₃^- concentration and weed flora may affect the competition between rice and weeds. In addition, vapour pressure deficit (VPD) affects leaf gas exchange and plant growth, which may alter the N uptake of plants. The study was conducted to evaluate the effects of N source on the competition between two rice varieties (NU838 and KD18) and two weed species (Echinochloa crus-galli and Solanum nigrum) at low and high VPD. Rice and weeds were grown hydroponically as monoculture or mixed culture with different N sources (75%/25% or 25%/75% NH₄⁺/NO₃^-). Independent of N source, rice and E. crus-galli took up a larger share of NH₄⁺, whereas S. nigrum took up a larger share of NO₃^-. A high correlation between water uptake rate and total N uptake rate was found in S. nigrum and E. crus-galli but not in rice. Moreover, in contrast to the other species, growth of S. nigrum was not reduced at high VPD, resulting in increased competitiveness and total N uptake of the weed. In competition, high NO₃^- increased the competitiveness of NU838 against E. crus-galli, but decreased the competitiveness of NU838 against S. nigrum. Our results suggest that increased availability of NO₃^- in aerobic rice soils may be disadvantageous for rice in competition with upland weeds, especially at high VPD, whereas, it may reduce pressure of common lowland weeds.

Keywords: Alternative wetting and drying, nitrogen source, plant competitiveness, water-saving irrigation, weeds in lowland rice

Contact Address: Duy Hoang Vu, Vietnam National University of Agriculture (VNUA), Dept. of Cultivation Sciences, Ngo Xuan Quang - Gialam, 131000 Hanoi, Vietnam, e-mail: vdhoang87gmail.com