Inoculant plant growth-promoting microorganisms enhance utilisation of urea-N and grain yield of paddy rice in southern Vietnam

Field experiments were conducted during successive rainy seasons in 2006 in the Chau Thanh district of southern Vietnam to evaluate the effects of an inoculant plant growth promoter product called BioGro and N fertiliser rates on yield and N and P nutrition of rice. The results indicated that inoculation with BioGro, containing a pseudomonad, two bacilli and a soil yeast, significantly increased grain and straw yields and total N uptake in both seasons, as well as grain quality in terms of percentage N. Nitrogen fertilisation increased grain and straw yields as well as total N and P uptakes significantly in both cropping seasons. The estimated grain yield response to added N was quadratic in nature with and without added BioGro. In the first crop, BioGro out-yielded the control up to 90 kg urea N ha(-1) whilst in the second season the beneficial effect of BioGro was observed up to 120 kg urea N ha(-1), indicating either an interaction of the inoculant with higher yielding seasonal conditions or a cumulative effect of BioGro application. In the first season, the estimated N rate for maximum grain yield was 103 kg N ha(-1) with BioGro while it was 143 kg N ha(-1) without BioGro. The maximum estimated grain yields were 3.21 and 3.18 t ha(-1) with and without BioGro, respectively. This information indicates that BioGro was able to save 40 kg N ha(-1) with an additional rice yield of 30 kg ha(-1) in the season. In the second rainy season, the estimated N rates for maximum grain yields were 94 and 97 kg N ha(-1) with and without BioGro, respectively. The estimated maximum grain yields were 3.49 and 3.25 t ha(-1) with and without BioGro, respectively. The two seasons' combined results indicate that application of BioGro improved the efficiency of N use by rice significantly, saving 43 kg N ha(-1) with an additional rice yield of 270 kg ha(-1) in two consecutive seasons at the experimental site. The extra efficiency was shown by the fact that the same yield of rice was obtained with about 40 and 60 kg less fertiliser-N that the maximum yields with urea alone in the two successive harvests on the same plots. (C) 2008 Elsevier Masson SAS. All rights reserved.