Rapid Yield Loss of Rice Cropped Successively in Aerobic Soil

Abstract

aimed at high yields. The low yield of upland rice, however, is largely a consequence of its production being Upland rice (Oryza sativa L.), commonly considered to be low limited to low harvest index (HI, ratio of grain to total yielding, can be high yielding if the genotype is improved for harvest index (HI) and the crop is grown relatively free from nutrient and biomass) varieties (George et al., 2001) and to infertile drought stresses. We examined whether high and stable rice yields or drought-prone uplands. could be obtained in aerobic soil. In four experiments of 1-to 3-yr Indications are that upland rice can also be high yieldduration, lime, N, and P were inputs for wet-season upland rice ing if the genotype is improved for yield and the crop 'UPLRi-5' in a favorable rainfed Oxisol. In a 3-yr experiment conis not subject to nutrient and drought stresses. With sisting of two crops per year in an irrigated Ultisol, different lowland improved upland rice, yields approaching 7 Mg ha Ϫ1 can and upland varieties were grown in limed and fertilized aerobic soil. be obtained, even in highly acidic upland soils, given First-season rainfed UPLRi-5 yield varied from 1.5 to 7.4 Mg ha Ϫ1 , adequate amounts of lime, N, and P (George et al., with low yields in fields receiving low early-season rainfall. With 2001). In the highly acidic soil of the 240-million-ha irrigation, the lowland hybrid 'Magat' yielded 7.8 Mg ha Ϫ1 vs. 2.1 Mg Cerrado region in Brazil, upland rice is a commercial ha Ϫ1 for traditional upland rice 'Lubang Red'. Magat's high yield was associated with a HI of 0.43 in contrast to 0.31 of improved upland crop in rotational systems (Guimarã es and Yokoyama, rice variety 'Apo' and 0.17 of Lubang Red. Whether the crop was 1998), producing about 5 Mg ha Ϫ1 with fertilizers and rainfed or irrigated, yield loss was rapid following the first season: irrigation (Stone et al., 1997). In China's Huang-Huai-Grain yields decreased by up to 73% for rainfed UPLRi-5 in the Hai River plains, with no soil acidity constraints, yields second to third season. In the irrigated upland, yield loss in the second approaching 7 Mg ha Ϫ1 have been observed for imto fourth season was reflected in a 16 to 79% decline in 10-wk biomass.proved upland rice lines on irrigated dryland (Huaqi Here, the 13-wk biomass in the fifth crop was only half that of the Wang, personal communication, 2000). simultaneously grown first-season crop. We conclude that while prom-

Prospects for Genetic Improvement to Increase Lowland Rice Yields with Less Water and Nitrogen

“…However, not all semi-dwarf varieties have high HI and high yield under aerobic condition. For example, short-stature IR72 produced only 4.9 t ha -1 with a HI of 0.28, which was lower than that of the tall upland variety Apo (George et al 2002). Apparently, IR72 does not have the same aerobic adaptation as PSBRc80 and Magat, although they are all semi-dwarf varieties and produce similar biomass under aerobic conditions.…”

“…However, large varietal differences in grain yield exist under aerobic conditions. George et al (2002) reported that a lowland hybrid variety (Magat) yielded 7.8 t ha -1 compared to 2.1 t ha -1 for a traditional upland rice variety (Lubang Red) when grown under aerobic conditions in the first season with supplemental irrigation. Magat's high yield was because of a harvest index (HI) of 0.43 in contrast to 0.31 of an improved upland rice variety (Apo) and 0.17 of Lubang Red.…”

“…Magat's high yield was because of a harvest index (HI) of 0.43 in contrast to 0.31 of an improved upland rice variety (Apo) and 0.17 of Lubang Red. George et al (2002) concluded that rice can be highly productive in aerobic soils if crop management is optimized for varieties with high HI and adapted to aerobic conditions. Aerobic rice is grown commercially in highly acidic soil of Brazil, producing about 5 t ha -1 with adequate supply of fertilizers and irrigation in rotational systems (George et al 2002).…”

“…George et al (2002) concluded that rice can be highly productive in aerobic soils if crop management is optimized for varieties with high HI and adapted to aerobic conditions. Aerobic rice is grown commercially in highly acidic soil of Brazil, producing about 5 t ha -1 with adequate supply of fertilizers and irrigation in rotational systems (George et al 2002). In China, aerobic rice yield potential approaches 7 t ha -1 in farmers' fields in the Huang-Huai-Hai Rice Plains .…”

“…Yield decline under monocropping of aerobic rice has been reported by George et al (2002) and Peng et al (2006). The causes of yield decline in the continuous aerobic rice system remain unclear.…”