RETARDED GROWTH OF LOWLAND RICE IN SALINE SOIL INOCULATED WITH NITROGEN-FIXER AZOTOBACTER

Low-land rice (Oryza sativa L.) cultivation in saline soils face some constraints include nitrogen availability. Saline-resistant nitrogen fixing bacteria Azotobacter are expected to increase supply nitrogen in saline soils. The objectives of the study were to determine the effect of liquid inoculant concentration of two Azotobacter isolates on early vegetative growth of lowland rice grown in potted saline soil. The greenhouse trial design was a randomized block design with seven treatments and four replications. The treatments were combination of isolates and Azotobacter liquid inoculant concentrations in single and mixed inoculation. The results showed that all plants experienced chlorosis and stunt due to high Electrical Conductivity. Inoculation of different isolates and concentrations did not influence the growth of lowland rice in soil with high EC at the end of experiment. Therefore, neither isolates nor concentration of Azotobacter could improve retarded-growth of lowland rice in saline soil.


INTRODUCTION
Limited arable land leads lowland rice cultivation in saline soils with low nitrogen availability.

Climate changes and irrigation
practices also increase the distribution of saline soil. In general saline soil located in coastal area affected by sea tidal and salt water intrusion. The main features of saline soil are sodium content between 8-15%, pH <8.5, EC > 4 dS/m (equivalent to 4 mmhos/cm) and sodium adsorption ratio >15% (Yan et al., 2015). Saline soil is one of the most destructive environmental conditions that causes major considerable decreased in plant growth, yield and crops quality (Shahbaz and Ashraf, 2013).
Plants grow in saline agroecosystem are not able to adsorb water as much as they need. Limited water absorption in saline and sodic condition lead to water scarcity (Assouline et al., 2015) and then low uptake of plant nutrient. Nitrogen (N) uptake restriction is always evidence in saline soil resulted in retarded early vegetative growth and plant stunting (Hoorn et al., 2001;Assouline et al., 2015). Rice is not resistance to saline soil but some cultivars are more tolerant compared to the others.

RESULTS AND DISCUSSION
The results showed that plant growth and performance was very poor due to salinity (Fig 1). Decreased of plant growth was evidence irrespective of Azotobacter treatments. Control plant that received no inoculation also suffered from salinity stress because of high EC of soil. All rice transplant was stunt and has yellow leaves that was not fully expanded. The severe toxicity was shown even at 3 days after planting (Fig 1).  The mean square of treatment on growth traits at 1 st , 2 nd and 3 rd week after planting was not significant.
Azotobacter inoculation didn't change plant height, number of leave at any week observation (Fig 1). We observe no fully expanded leave in this pot trial. Either plant height or number of leaves were lower than that those of rice grown in non-saline soil.

The result found that
Azotobacter inoculation to rice in saline soil didn't affect number of stem (tiller) of individual pot (Fig 2).
The increase of tiller in each treatment plants from 1 st to 3 rd week was evidence but they are thin and weak. The number of tiller at 3 rd week was 6.3 in average. Rice grown in normal soil had around 8 tiller at 15 days after planting that increased to around 27 at three weeks after (Jalil et al., 2015). Effect of isolates and concentration of Azotobacter liquid inoculant on number of expanded leaves of rice grown in saline soil at 3 weeks after transplanting. A: control, B: isolate S1, 0.1%; C: isolate S1, 0.5%; D: isolate S2, 0.1%; E: isolate S2, 0.1%; F: isolates S1 and S2; 0.1%; G: isolates S1 and S2; 0.5%.
Higher EC after experiment in all pots was a results of transpiration by which salt accumulation was occured surrounding the roots. The increase in EC was also influenced by low organic matter (Carmo et al., 2006) since the soil contain only low organic carbon (0.65%). Application of 50 g cow manure to 5 kg soil was too low to reduce soil EC and maintain Azotobacter proliferation and their enzymatic activities. In all treatments, increased in pH might be caused by the degradation of organic matter by heterotrophic that use organic matter as a carbon source.
Since decades, decomposition of organic matter was verified to increase OHconcentration and hence the pH (Hopkins et al., 1990).
Decrease of early vegetative growth in saline soil of this pot experiment was clear since rice is a grain crops sensitive to saline soil mainly in the early stage of growth (Makihara et al., 1999;Reddy et al., 2017). can reduce the opening of stomata (Silva et al, 2008). High salt solubility inhibit the absorption of water and nutrients, resulting in low uptake of N (Hoorn et al., 2001).