Effects of Different Soil Amendments on the Yield of Salt-alkali Tolerant Rice

HE Zhong-xiang, LI Chang-jun, LIU Shang-ru, LUO Hai-yan, PENG Hua, ZHU Jian, JIAN Yan

Hunan Institute of Agro-Environment and Ecology, Ministry of Agriculture Key Lab of Agro-Environment Institute in the Midstream of Yangtze River Plain, Key Lab of Prevention, Control and Remediation of Soil Heavy Metal Pollution in Hunan Province, Changsha 410125, PRC

Abstract Aiken base silicon, advanced silicon, activated carbon, desulphurization gypsum, ferric phosphate, humic acid, aluminum dihydrogen phosphate etc. were used as raw meterials to conduct the compound development of salt-alkali soil amendents, and the salt-tolerant rice "Chaoyouqianhao" was used as the test variety to verify the effect of increasing yield under simulated salt stress environment. The results showed that at the tillering stage, the growth indexes of rice plant in the treatment with soil amendements were better than that in the treatment without soil amendments (CK2). Of which, T5 and T6 had the best effect, and the dry weight of rice plant increased by 40.99% and 70.06%, respectively, compared to the CK2. At the maturity stage, T5, T6 and T7 had a better effect on the increase of rice yield. Of which, T5 had the highest yield, up to 6 533.32 kg/hm2, which increased by 29.97%compared to the CK2. Focused on the soil amendments formulation in the T5 and T6,the two formulations all contained ferric phosphate, humic acid, calcium magnesium phosphate fertilizer, indicating that these substances played an important role in saline-alkali soil improvement.

Key words Salt stress; Soil amendment; Formulation; Salt-alkali tolerant rice

1. Introduction

In China, there are about 99 million hmof saline soil which have not been used or the utilization rate is not high, accounting for about 10% of China's arable land area. Soil salinization will cause soil consolidation, poor water retention and water permeability and decreased fertility in soil, limiting soil nitrogen transformation, and further affecting the absorption of water and nutrient, and hindering the growth of crop. Rice is a moderately saline-alkali sensitive crops, whose yield is easily reduced by saline-alkali stress. Therefore, soil salinization is the main factor limiting the stable development of rice production in saline-alkali rice planting area. Recently, how to improve the tolerance of rice under saline-alkali stress and promote rice yield has attracted the attention of researchers.

At present, the main measures to control salinealkali soil at home and abroad are divided into three categories: engineering measures (soil replacement improve, washing salt with fresh water, laying the isolation layer,

etc

.), biological measures (plant improvement, microbial symbioses,

etc

.) and chemical measures (chemical washing, soil amendments,

etc

.).In comparison, engineering measures are expensive and difficult to construct, biological measures pose some limitations because of limited resouces,and chemical measures with simple operation and accessible raw materials, are ideal saline-alkali soil improvement methods. Therefore, soil amendments have been widely used to improve and optimize saline-alkali soil and enhance the salt tolerance of crops recently. In this study, silicon-based materials and ferric phosphate were used as the main raw materials to develop salt-alkali soil amendments and compare the effects of different soil amendments on rice growth and yield increase under salt stress, so as to provide scientific basis for the development and utilization of saline-alkali soil.

2. Materials and Methods

2.1. Materials

The salt-tolerant rice "Chaoyouqianhao" was used as test rice variety. Aiken base silicon, advanced silicon, activated carbon, desulphurization gypsum,ferric phosphate, humic acid, aluminum dihydrogen phosphate

etc

. were used as raw meterials. Paddy soil located in Gaoqiao base of Hunan Academy of

Agricultural Sciences was used as test soil. It was collected, dried, grinded, sieved and placed in a salt pood. Sun-dried sea salt (Shandong Yantai Laizhou Haijing Salt Chemical Company) was added until the salt content of soil was 0.6%.

2.2. Methods

The experiment was conducted in Gaoqiao base of Hunan Academy of Agricultural Sciences from June to October. Chaoyouqianhao was planted as middle-season rice and seedling was transplanted by hand. 32 artificial salt ponds were prepared. Each salt pond was 3.75 mwith impermeable membrane for isolation. The depth of the salt pond was 60 cm,the depth of backfill soil was 40 cm, and the flooding depth was controlled to 10 cm. The salt content of paddy soil was adjusted to 0.6% by using dried sea salt. 32 salt ponds were divided into 8 groups, T1～T7:applying different compound soil amendments (Table 1); CK2: no applying soil amendments. In addition,4 conventional soils were prepared as CK1 without soil amendments. One week before rice transplanting,soil amendments with an amount of 200 kg/667 mand base fertilizer were applied scatteredly together,then mixed by machine. 100 kg/667 mof compound fertilizer and 5 kg/667 mof urea were applied as base fertilizer.

2.3. Sample collection and determination

At the tillering stage, 5 plants were selected from each plot to determine the SPAD value of upper leaves in rice plant using SPAD-502 chlorophyll meter, and the average value was taken as the SPAD value of theleaves; meanwhile, 5 consecutive representative rice plants with consistent growth from each plot were taken to dertermine the plant height, death rate of seedlings, number of non-healthy seedlings

etc

. At the mature stage, 5 consecutive representative rice plants with consistent growth from each plot were taken to dertermine the number of productive ear, 1 000-grain weight and record the rice yield (the value excluding moisture content).

Table 1 Experiment design

2.4. Data processing

IMB SPSS 21.0 was used for statistical analysis.Least Significant Difference (LSD) was used for significance analysis. Excel 2010, Graphpad prism 9,Origin 2016 were used to make graph.

3. Results and Analysis

3.1. Effects of different soil amendments on the growth of rice at the tillering stage

3.1.1. The rice growing states at the tillering stage

As shown in Table 2, compared with the CK1,the death rate of seedling increased, healthy seedling ratio decreased and plant height at the tillering stage decreased in the CK2. It indicated that salt stress had strong inhibition effect on rice growth. The rice death rate, healthy seedling ratio, plant biomass and plant height in the T1～T7 were superior to CK2. This indicated that applying soil amendments could achieve the effect of reducing salt stress in rice, especially T5 and T6 had strong promoting effect on salt tolerance of rice, and plant dry weight increased by 40.99% and 70.60% compared to CK2, respectively.

3.1.2. SPAD value of rice leaves at the tillering stage

As shown in Fig. 1, the SPAD value in theCK1 was significantly higher than that in the other treatments, indicating that chlorophyll content in rice leaves decreased significantly under salt stress. The SPAD value in the T1～T7 was higher than that in the CK2, whereas the difference was not obvious. This indicated that applying soil amendments could increase chlorophyll content in rice leaves under salt stress.

Table 2 The rice growing states in the different treatments

3.2. Effects of different soil amendments on rice yields

Fig. 1 SPAD value of rice leaves in the different treatments

As shown in Fig. 2～4, the yields in the T5, T6 and T7 were significantly higher than that in the CK2,but they had no significant difference from that of the CK1. Of which, the yiled in the T5 was the highest, up to 6 533.32 kg/hm, increased by 29.97% compared to the CK2, and the 1 000-grain weight and the number of effective ear in the T5 were 23.46 g and 207 400 ears/667 m,respectively. Followed by T6 and T7, in which the yields were 5 893.32 and 5 906.64 kg/hm, increased by 17.24% and 17.50% compared to the CK2,respectively. Moreover, the yield in the T1 was slightly higher than that in the CK2, while the yield in the T2, T3 and T4 were lower than that in the CK2,but there were no significant differences between them. Compared with T2, T3 and T4, T5, T6 and T7 contained ferric phosphate, indicating that the compound of soil amendments with ferric phosphate as the main raw material had a stronger yieldincreasing effect.

Fig. 2 Number of effective ears of rice in the different treatments

Fig. 3 1 000-grain weight of rice in the different treatments

4. Discussions

Fig. 4 Rice yield in the different treatments

Rice plant biomass, plant height and death rate of seedling can directly reflect the growth of rice plants under stress. Under salt stress, rice plants will be subjected to different degrees of influence, plant biomass, plant height and other indexes will decrease, the development of rice plant will be blocked or even death will occur. In this study, silicon-based materials and ferric phosphate were used as the main raw materials to explore the effects of different compound soil amendents on the growth and yield of rice under simulated salt stress environment, the results showed that at the tillering stage, the growth indexes of rice plant in the treatment with soil amendements were better than that in the treatment without soil amendments (CK2), indicating that applying soil amendments could alleviate the inhibition of salt stress on the rice growth and improve the gowth status of rice under salt stress. ROMEROARANDA M R,

et al

. showed that the addition of silicon can significantly improve the biomass of wheat at all stages under salt-alkali stress. LIANG Y C

et al

.found that after adding exogenous silicon, chlorophyll content and COassimilation rate of leaves in barley increased, leaf area increased,biomass and plant height also significantly increased.Meanwhile, the addition of silicon fertilizer also can improve the activities of CAT, SOD and APX, and improve the accumulation of ROS in plants under salt stress. However, whether it is directly regulated by silicon or indirectly regulated by various hormones remains to be further studied. In this study, except for T6, all the compound soil amendments in the other treatment were based on activated silica, therefore, the increase of biomass and plant height at tillering stage might be related to the addition of silicon fertilizer.However, T6 had the highest plant biomass at the tillering stage, this maybe because that the organic matter such as humic acid, activated carbon,

etc

. in the T6 possess massive CEC, macromolecular structure and functional groups, which could improve soil pore structure, enhance soil water and fertilizer retention capacity, reduce EC and water-soluble Nacontents in saline-alkali soil, improve the absorption of Kby plants, and promote the absorption and utilization rate of nutrients by plants. Meanwhile, Cain calcium magnesium phosphate fertilizer could also replace Nain soil colloid and form competitive adsorption with plants, thus reducing the absorption of Naby plants.In addition, calcium magnesium phosphate fertilizer not only could significantly increase the contents of available calcium and phosphorus in soil, but also could significantly increase the content of silicon in soil, which may be the reason for the best effect in the T6 at the tillering stage.Previous studies showed that different soil amendments all had increasing effect on rice.Of which, the application that ZHU J L

et al

.used compound soil amendments with gypsum powder and superphosphate as main raw materials to improve saline alkali soil had better increasing effect on rice,and the rice yield was 9 689 kg/hm. Nevertheless, the application amount was quite a lot (34.5 t/hm) and the salt content in soil was less (0.12%), this indicated that the difference of improver effect is related to the amount and type of soil amendments. In this study,the application amount of all soil amendments was less, only 3 t/hm, whereas the highest yield reached up to 6 533.32 kg/hm, which increased by 29.97%compared to the CK2. At the mature stage, the yields in the T5, T6 and T7 were higher than that in the other treatments, which may be related to the existence of ferric phosphate in the three treatments. Because ferric salts could improve the physical and chemical properties of saline-alkali soil, improve soil and water retention ability, and significantly increase antioxidant enzymes activity. In addition, the absorption and utilization efficiency of ferric ion was greatly reduced under saline-alkali stress, which seriously affected the normal growth and metabolism of plants. Because ferric was one of the indispensable trace elements in rice, it played an important role in the growth and development of rice. On the one hand, ferric could participate in photosynthetic electron transport in the form of ferredoxin, promoting plant photosynthesis,which was also consistent with the SPAD value of rice leaves in this study. On the other hand, ferric also participated in the cycle of the cell free radical enzyme system, such as the transformation of catalase (CAT)and peroxidase (POD), which could further improve the activity of antioxidant enzyme system and inhibit membrane lipid peroxidation under salt stress.

In conclusion, it was feasible to improve the salt tolerance and yield of rice by adding soil amendments under salt stress. However, the mechanisms of different compound soil amendments improving rice salt tolerance still need to be studied. After finding out the mechanism, we can select the raw materials purposefully and develop soil amendments with high efficiency and low price.