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

Abstract

Abstract. Increasing yield potential of lowland rice remains to be the top priority in rice geneticimprovement programmes, because rice farmers' primary concern is still grain yield and world rice production has to increase by 1% annually in the next 20 years to meet the demand of the growing population. Improvements in yield potential of irrigated lowland rice were achieved under ample supply of water and nutrients. Water use efficiency (WUE) and nitrogen use efficiency (NUE) were seldom included in the breeding objectives for irrigated lowland rice. Scarcity of freshwater resources has threatened the production of the flood-irrigated rice crop, and excessive use of N fertilizer is causing environmental concerns. We have to increase lowland rice yield with less water and N. Newly developed crop management strategies have proven to be effective in increasing WUE and NUE. Several watersaving technologies such as alternate wetting and drying (AWD) and aerobic rice system have been developed to increase the water productivity of rice. However, yield penalty occurred when these watersaving technologies were practised with current varieties. New varieties have to be developed to reduce the yield loss under AWD and aerobic rice system in order to increase WUE further. Direct selection for WUE under flood-irrigated lowland conditions may have a negative impact on grain yield under watersaving strategies. Optimizing the timing and rate of N application to synchronize supply and demand of N by the crop has resulted in a great reduction in fertilizer-N input without yield loss and greater NUE. Genetic improvement of NUE has not been achieved in rice. Genotypic variation in NUE has been reported in many studies. Plant traits that are associated with high grain yield and high NUE should be identified so that breeders are able to use these traits easily as selection criteria in the breeding programme to develop N-efficient varieties without sacrificing rice yield potential. New breeding techniques such as development of F 1 hybrids, marker-aided selection, transformation and genetic engineering should be combined effectively with the empirical breeding method in order to increase rice grain yield with less water and N.

Current Status and Challenges of Rice Production in China

“…In the past, most progress in the improvement of rice yield potential was achieved when water and nutrients were amply supplied (Peng and Bouman, 2007). China has been at the forefront in developing high-yielding varieties using semidwarf, hybrid, and new plant type breeding approaches.…”

“…Therefore, it is not easy to achieve high yields with the "super" rice varieties consistently across seasons and locations. Because of water scarcity and environmental concerns, the challenge is to increase rice yield with less water and less chemicals (Peng and Bouman, 2007). To achieve this goal, new breeding techniques such as marker-aided selection, transformation, and genetic engineering should be combined effectively with the empirical breeding method.…”

Nitrogen economy in relay intercropping systems of wheat and cotton

“…The N-economy of a crop is the result of many processes occurring in the soil, crop and atmosphere and can be quantified by a wide variety of parameters (Peng and Bouman 2007;Spiertz and Vos 2005). In this study, we determined N-uptake in relation to DMyield, physiological N use efficiency, and N-dilution in biomass over time.…”

Nitrogen, sustainable agriculture and food security. A review

“…Surprisingly, the variation in parameter values for nitrogenuse efficiencies does not differ much between low-and highinput systems. Genetic improvements of rice are most effective in enhancing physiological N-use efficiencies (Peng and Bouman, 2007), while applying best management practices can raise apparent N recoveries (Campbell et al, 1995;Cassman et al, 1993) It is concluded that N supply should match N demand in time and space -not only for single crops, but for a crop rotation as an integrated system -to achieve a higher agronomic NUE. Alleviating factors that limit growth -such as drought, flooding, pests and diseases -will be most effective in increasing the apparent N recovery.…”

“…-improved resource use; a better timing of nitrogen and water supply by time-and site-specific management can avoid stress at critical growth stages. More productivity per unit of water will lead to increased yields and thus higher NUE (Peng and Bouman, 2007). -improved cropping systems; farmers can vary the timing of sowing/planting and the choice of crops in a cropping sequence to make a better match of the genetic make-up of a crop and the growing conditions determined by climate, soil and pests (Hobbs et al, 2008;Ladha et al, 2005).…”