Nitrogen Source Affecting the Competitiveness Between Lowland Rice and Weeds under Low and High Vapor Pressure Deficit
Duy Hoang Vu1, Sabine Stürz2, Folkard Asch2
1Vietnam National University of Agriculture (VNUA), Dept. of Cultivation Sci., Vietnam
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 Sci., Ngo Xuan Quang - Gialam, 131000 Hanoi, Vietnam, e-mail: vdhoang87gmail.com