Control of secondary salinization in soils through Effective Microbes
X.H. Shao¹, D.Y. Liu¹, P. Jiang² and W.L. Cao²

1 Hohai University of Water Conservancy & Hydro-power Engineering, Nanjing 210098, P.R. China

2 Division of Agriculture Water Conservancy, Zhejiang Provincial Bureau of Water Resources, Hangzhou, 310009, P.R. China

Introduction
Through the establishment of drainage-irrigation system combining with biological engineering measures, the salt-affected soils in China are gradually ameliorated and controlled. However, there are still secondary salinization soils of 36.9 million ha., of which cultivated ones mainly occur in the Huang-Huai-Hai plain, the western plain of Northeast China, the Great Bend of the Yellow River and the Inland of Norwest China as well as a small part of eastern coast with a total area of 6.24 million ha., taking up about 7% of the country’s cultivated land (Gong and Luo, 1997). These cultivated lands affected by salts are mostly formed due to irrigation with neglect of the drainage system notably in the (semi) arid region which are great obstacles to the development of agriculture.

Use of beneficial and effective microorganisms as microbial inoculants in agriculture is a promising new technology (Shao et al., 2001). It has been shown to be effective in improving soil health and quality, and raising the growth yield and quality of crops (Li et al., 1999). But few researches are conducted considering the amelioration of salt-affected soils by use of EM technology. In this paper, EM technology combining with subsurface drainage is applied in the rice production in Ningxia and Zhejiang provinces to see the effectiveness of EM in controlling the secondary salinization.

Material and methods

1. Preparation of EM bokashi
EM bokashi is an organic fertilizer prepared by adding water (500ml), molasses (8ml) and effective microorganisms (EM) (8ml) to a thoroughly mixed material of rice bran and animal manure (4.7Kg) then anaerobically fermented for 2 weeks. Equal amount of rice bran and animal manure without addition of EM was also fermented to produce traditional Farmyard Manure (FYM). The chemical properties of EM Bokashi used are presented in Table 1.

2. Description of the field experiment
The field experiments were conducted from 2000 to 2001 in the saline soils of Qianjin Farm in the Autonomous Region of Ningxia and Baiquan town, Zhoushan city in Zhejiang Province respectively. Qianjin Farm is situated in arid area with the average annual rainfall of 186mm, whereas Baiquan town is located at the coastal humid zone with the average annual precipitation of around 1200mm. The experiment consisted of two blocks with and without the field subdrainage system. The subdrainage system used PVC tubes of 5.5cm diameter with the depth of 1.1m and the spacing of 15m respectively. Total eight plots (each of size 100mx30m) were given separately at two blocks of both sites containing a single replicate of each treatment.

The following treatments were applied to designated plots each year in rice production.

1) Chemical fertilizer (N, P) without subdrainage;

2) Farmyard manure (10t ha^-1) + Chemical fertilizer (N, P) without subdrainage;

3) EM bokashi (10t ha^-1) + Chemical fertilizer (N, P) without subdrainage;

4) EM bokashi (20t ha^-1) without subdrainage;

5) Chemical fertilizer (N, P) with subdrainage;

6) Farmyard manure (10t ha^-1) + Chemical fertilizer (N, P) with subdrainage;

7) EM bokashi (10t ha^-1) + Chemical fertilizer (N, P) with subdrainage;

8) EM bokashi (20t ha^-1) with subdrainage;

Chemical fertilizer was applied according to local recommendations as basal and dressing applications. Farmyard manure and EM bokashi were applied as basal and mixed well in the soils up to 15cm depth. Each treatment was adjusted to contain almost equal amount of N and P nutrients at each site. The physio-chemical properties of soils tested were also listed in Table 1.

Rice and soils were managed based on the local methods and traditions. Underground water table, soil moisture and EC of 0-100cm soil profiles, water irrigated and drained were measured in each treatment by use of the observing well, netron probe and salt sensor as well as water gauge in the field. Laboratory analysis and measurement of coefficients related to soils and rice crop were strictly based on the methods of Soil Physico-chemistry Analyses (Agriculture Press, 1989).

Results and Discussion

1. Effect of EM bokashi on soil properties

It could be seen from Table 2 that treatments received EM had a higher microbial biomass level, organic matter, alkaline N, available P and CEC than chemical fertilizer treatment as well as FYM + chemical fertilizer treatment whether with subdrainage or without subdrainage. The lowest soil bulk densities in both experimental sites occurred at 0-20cm where the soils were treated with 20t ha^-1 EM bokashi with subdrainage system. Lower bulk densities resulted from EM bokashi (10t ha^-1) and FYM + chemical fertilizer compared with chemical fertilizer only. Generally, highly productive agricultural soils have bulk densities of less than 1.4gcm^-3 which have a well-developed structure, better porosity and permeability. Results showed that bulk densities of saline soils had reduced to less than 1.40gcm^-3 after two years of amelioration with application of 20t ha^-1 EM bokashi. Therefore, EM bokashi was very effective in raising the salt-affected soil fertility both physio-chemically and biologically.

Before field experiments, the threats of secondary salinization did existed in the both locations with total soluble salt contents of 1.21%, 0.98%, 0.33%, and 0.28% respectively at depths of 0-20cm and 0-100cm. The dates of July and Sept in 2000 represented the processes of leaching just after irrigation and movement upwards of the salt during drainage respectively. The results showed EM bokashi with subsurface drainage treatment was the most effective in controlling the secondary salinization with maximum desalinization degrees at depths of 0-20cm and 0-100cm in both experimental sites. Subdrainage system had no doubt predominant contribution to depressions of total soluble salt content. Nevertheless, EM bokashi also played greater roles in the control of secondary salinization compared with chemical fertilizer treatment. The reasons were possibly that application of EM bokashi improved the permeability and aeration capacity of soils which increased the leaching of salts.

3. Effect of EM bokashi on yield and quality of rice grain

Conclusions
The obtained analytical results lead to the following conclusions:

1. EM bokashi treatments evidently increased soil fertility by increasing soil organic matter content, CEC and available nutrients, by improving soil porosity and permeability and by increasing the micro-biomass of soils.
2. EM bokashi with subsurface drainage treatments were the most effective in controlling the secondary salinization of soils and raising rice grain yields and quality compared with FYM and chemical fertilizer treatments.
3. EM technology could sufficiently reduce or stop the amount of chemical fertilizers application, thereby improving the agricultural environment and guaranteeing the sustainable development of agriculture.