Do water-saving ground cover rice production systems increase grain yields at regional scales?

Our study revealed the following findings: (1) Across all sites GCRPS significantly increased grain yield by on average 18%. Statistical analysis allowed us to classify three different groups of yield performance within the 36 paired sites: (a) group of significant increase (SI; n = 22) with increases in yields on average 32%, (b) group showing no significant increase (NI; n = 9), here yields increased on average 6%, and (c) sites with grain yields showing a small (−8%), but non significant decrease (ND; n = 5). (2) Shoot dry biomass, number of productive tillers, spikelets per square meter and percentage of filled grains were significantly larger for GCRPS as compared to Paddy systems. (3) No significant differences in soil physical and chemical properties were found for the 0-20 cm layer between GCRPS and Paddy systems. (4) Significantly higher soil temperatures observed in GCRPS during the first month after transplanting were only found in the SI sites, which showed that higher temperature during this critical period was the decisive factor for GCRPS-induced yield enhancement. (5) The average δ13C of plant leaves and soil redox potential were significantly higher in GCRPS than Paddy for the SI group only. In-detail analyses of the 5 pairs showing decreases in yields (ND) between GCRPS and Paddy systems revealed the lack of significant effects observed in some key parameters such as soil temperatures during the first month, δ13C of plant leaves and soil redox potential. These facts strongly suggested that unnecessary excess water was used, thus hampering GCRPS-induced increases in soil temperature and grain yields, and unequivocally signaling that appropriate water management by farmers is crucial for the successful implementation of GCRPS. Our study demonstrates the large potential of GCRPS to increase grain yields in regions where rice growth is both limited by low temperatures and water scarcity.