Effects of Soil Improver on Wheat in SalineAlkali Lands in the Yellow River Delta

Liang DONG Shenzhong TIAN Zeqiang SUN Xuejun WANG Zhaohui LIU Ruiqin LI Ye TIAN Deshui TAN Jiafa LUO

Abstract Field experiment carried out to test the effects of soil improver on wheat yield and soil physicalchemical properties. The results indicated that soil improver could optimize soil aggregates structure， decrease soil bulk density， soil pH and soil salt content， increase soil organic matter and 1 000grain weight， thereby enhancing wheat yield. With the increase of soil improver application amount， soil physicalchemical properties became better and wheat yield increased. However， there was no significant difference in the treatments with the application amounts of 3%， 4% and 5%. In addition， the treatment of reducing nitrogen showed no superiority in soil physicalchemical properties and wheat yield， indicating that sufficient nitrogen was essential for the growth of wheat.

Key words Soil improver， Salinealkali land; Wheat

The Yellow River Delta has superior location conditions， abundant natural resources and broad development prospects， mainly reflected in the advantages of land resources. It has 540 000 hm2 of unused land， which is an important reserve land resource in China. Since the evaporation in the Yellow River Delta is far greater than precipitation， together with the high underground water level and large degree of mineralization is large， the soil salinization is as high as over 70%[1]. In turn， the serious soil salinization has made the ecological environment very fragile[2-4].

On December 1， 2009， the State Council of the Peoples Republic of China passed the "Development Plan for HighEfficiency Ecological Economic Zone of the Yellow River Delta". As a starting point， the development of the Yellow River Delta region has risen to a national strategy and has become an important part of the national regional coordinated development strategy of China. Moreover， it has been formally incorporated into the key construction areas of the National "Eleventh FiveYear Plan" of China. At the same time， the Yellow River Delta is also the main body of the central and northern wings of the "one body and two wings" of regional economic development in Shandong Province， and its strategic position is very important.

With the construction and development of the highefficiency ecological economic zone in the Yellow River Delta， China has issued a series of policies for the development and utilization of lowyield soils. With the support and encouragement of current policies in China， it is of great economic and ecological significances to carry out rational development and efficient use of largescale salinealkali land. One of the major problems restricting the development and utilization of the Yellow River Delta at this stage is the problem of poor soil quality due to high soil salinity. At present， all countries in the world have strengthened the improvement of salinealkali land[5]. For a long time， the improvement of salinealkali land has adopted engineering measures， such as freshwater leaching on salinealkali land， and alien soil transferring soil salinity. It is also a common method to add chemical improvers and plant salttolerant plants[6-7]. The improvement of salinealkali land should not only take into account the cost of soil improvement input， whether the soil salinity can be reduced to the level allowed by crop growth， but also the longterm sustainable use of the improved soil and the impact on the regional ecological environment. Therefore， it is the goal and direction for the study on salinealkali soil improvement to explore highefficiency， lowcost， environmentallyfriendly and practical salinealkali land improvement methods and improved materials. It has been found that the application of chemical improvers such as phosphogypsum in salinealkali soils can improve the salinealkali soil by reducing exchangeable sodium in the soil and improving soil physical and chemical properties[8]. In addition， it is also an effective method to use organic fertilizers， zeolites and other materials for improvement[9].

In this study， a salinealkali soil improver was developed with humic acid as the principal component. Field experiment was carried out to verify the effect of the selfdeveloped soil improver on the wheat planted in the salinealkaline land in the Yellow River Delta， so as to provide a scientific basis for the largescale application and promotion of the improver.

Materials and Methods

Test materials

Test fertilizers： urea， heavy calcium， potassium sulfate， all commercially available fertilizers.

Tested salinealkali soil improver： selfdeveloped soil improver with humic acid as the main component.

Test crop： wheat of variety Luyuan 502.

Test soil

Located at 37°17′30.6″N， 118°36′59.62″E， the test site is in the Yellow River Delta Modern Agricultural Experiment Demonstration Base of Shandong Academy of Agricultural Sciences （Dongying Base for short）. It has a warm temperate monsoon climate with the annual average temperature of 12.2， average rainfall of 543.3 mm， frostfree period of 203 d， annual sunshine hours of 2 440.3 h， and annual accumulated temperature greater than 0 of above 4 600. It also has sufficient light and heat resources and four distinct seasons. The soil in this area is dominated with mild coastal saline soil.

The composition of 0-20 cm soil aggregate structure was as follows： > 2.0 mm soil particles accounted for 10.43%， 1.0-2.0 mm soil particles accounted for 9.45%， 0.5-1.0 mm soil particles accounted for 6.01%， 0.25-0.50 mm soil particles accounted for 13.26%， < 0.25 mm soil particles accounted for 60.85%.

Test methods

There were a total of 7 treatments in the test， and the contents of each treatment and the amount of fertilizer are shown in Table 2.

The test was carried out from October 5， 2014 to June 14， 2015. In Dongying base， a uniform land field was selected to test the effects of the soil improver. Each treatment had 3 repetitions， and the test plots were arranged in random blocks. Each plot was set to 8 m≠5 m， with an area of 40 m2. Treatments with the soil improver were carried out to different plots according to the test design， and the application amounts of the soil improver were calculated according to the total weight of fertilizers. The soil improver was applied by mixing with fertilizers. Treatments 2 and 3 were fertilized according to local fertilization methods， which had the basal application of 60% of the P， K and N fertilizers， and topdressing the other 40% at the jointing stage. In treatments 4， 5， 6 and 7， the fertilizers were applied at one time. Each plot was harvested separately， and then the yield and 1 000grain weight were recorded. The soil was collected at the harvesting time to investigate soil organic matter， salt content， pH value and aggregate structure， which were determined according to Lus Methods for Soil Agrochemical Analysis[10].

Results and Analysis

Effects of soil improver on soil physicalchemical properties

Effect of soil improver on soil aggregate structure in 0-20 cm soil layer

Soil aggregate structure is one of the basic fertility properties of soil and is of great significance in the agricultural use of soil. The composition of soil particles determines the soil texture， which directly affects the retention and movement of soil water， fertilizer， gas， heat， and is closely related to the growth and development of crops. Soil particle size classification was carried out according to the Kachinsky system， that is， >1 mm for gravel， 0.5-1.0 mm for coarse sand， 0.25-0.50 mm for medium sand， and <0.25 mm for fine sand[11].

As shown in Fig. 1， the proportion of gravels of >1 mm was 18.90%， 18.63%， respectively in the soil without fertilization and with conventional fertilization treatment， both of which were higher than the proportion in the optimized fertilization treatment and optimized fertilization+improver treatment. The proportion of fine sand of < 0.25 mm was 58.34% and 59.01%， respectively in the 2 treatments， which were also higher than the optimized fertilization treatment， optimized fertilization+improver treatment. The results indicated that in the treatments with optimized fertilization， optimized fertilization+improver， large gravel and fine sand had low proportions， and the composition of soil particles with different sizes was more reasonable and coordinated.

Compared with the optimized fertilization， soil of the optimized fertilization+improver treatment had higher proportions of gravel and fine sand， indicating that the addition of soil improvers could improve soil aeration and water permeability and improve soil plantability.

Under the same optimized fertilization amount， with the increase of the application amount of soil improver， the proportions of gravel and fine sand decreased， and the composition of soil particles were more coordinated in the treatment with optimized fertilization+5% soil improver.

Under the same soil improver application amount， although the fertilization amount decreased in T7， which had nitrogen reduction， the proportions of large gravel and fine sand increased by 0.34 and 0.79 percentage points， respectively.

Effect of soil improver on soil bulk density

Soil bulk density is an important physical trait that reflects and regulates soil water， fertilizer， gas， heat and other factors， affecting plant root penetration， soil water content， soil aeration and water and fertilizer utilization[11].

As shown in Table 3， the soil bulk density of 0-20 cm and 20-40 cm slightly increased or remained the same in the treatments of conventional fertilization and optimized fertilization. The reason was that the single application of chemical fertilizers increased the aggregate dispersion coefficient， made soil stiff and soil body sticky， and reduced porosity. The application of inorganic and organic compounding could improve this situation.

Under the same fertilization amount， the soil bulk density reduced after adding soil improver to the optimized fertilization treatment. The decrease in 0-20 cm soil layer was 1.99%-5.96%， and the decrease in 20-40 cm soil layer was 1.97%-3.29%. It showed that the soil improver could reduce soil compaction and increase soil aeration and water permeability.

With the same application amount of soil improver， soil bulk density also decreased after decreasing the application amount of nitrogen fertilizer， indicating that proper reduction of chemical fertilizers had a certain effect on maintaining good soil properties.

In general， both the application of soil improver and nitrogen reduction could reduce soil bulk density， and the soil bulk density was reduced to optimize the soil good structure.

Effect of soil improver on soil organic matter contentSoil organic matter is not only a source of mineral nutrients and organic nutrients for plants， but also an important factor in the formation of soil structure. Therefore， soil organic matter directly affects soil fertility， water retention， buffering effect， cultivability and ventilation conditions[11].

As shown in Table 3， compared with the nonfertilization treatment， the soil organic matter at soil layers of 0-20 cm and 20-40 cm in the conventional fertilization treatment was increased by 0.03 and 0.02 percentage points， respectively. Compared with the conventional fertilization treatment， the soil organic matter at soil layers of 0-20 cm and 20-40 cm with optimized fertilization treatment was increased by 0.06， 0.07 percentage points respectively. Under the same amount of fertilization， compared with optimized fertilization， the soil organic matter at soil layers of 0-20 cm in the treatments added with soil improver increased 0， 0.08， 0.02 percentage points， and the increase was 0.02， 0.08 and 0.02 at the soil layer of 20-40 cm. Under the conditions with equal application amount of soil improver， the soil organic matter at the soil layers of 0-20 cm and 20-40 cm was decreased by 0.03， 0.06 percentage points after the reduction of nitrogen fertilizers.

Both fertilization and the application of soil improver could increase soil organic matter content. The reason was that fertilization and applying soil improver increased crop biomass， thereby increasing the soil organic input to the roots， stubbles and fallen leaves.

Effect of soil improver on soil pH

Soil pH has great influence on soil fertility， crop growth and nutrient availability. Therefore， attention should be paid to soil pH in agricultural production， and measures should be taken actively according to the crops and operational requirements[11]. As shown in Table 3， compared with the treatments with no fertilizer application， soil pH decreased both in the fertilization treatments and the treatments with soil improver. The reason was that fertilization and the application of soil improver could promote the growth of crops， the development of crop roots， and soil improver could adjust soil physical structure， reduce evaporation， improve aeration， and inhibit the accumulation of salt in the surface soil， and thus reduce soil pH. However， there was no significant difference and regularity in the pH value at the soil layers of 0-20 cm and 20-40 cm in the treatments with conventional fertilization， optimized fertilization and the treatments with different application amounts of soil improver.

Effect of soil improver on soil salt content

Soil salt content is an indicator of soil salinization[11]. As shown in Table 3， compared with the treatment without fertilization， soil pH slightly increased in the treatment with conventional fertilization， while decreased in the treatments with optimized fertilization and with the application of soil improver. Under the same fertilization amount， compared with the optimized fertilization treatment， the soil salt content at the soil layer of 0-20 cm was decreased by 0.02， 0.01 and 0.02 percentage points after adding 3%， 4% and 5% of soil improver， and the decrease was 0.02， 0.01 and 0.03 percentage points at the soil layer of 20-40 cm. In the treatments with the same application amount of soil improver， the soil salt content in the nitrogen reduction treatment was decreased by 0.02 and 0.01 percentage points at the soil layer of 0-20 cm and 20-40 cm， respectively.

Effects of soil improver on 1 000grain weight and yield of wheat

The 1 000grain weight of wheat is an important component factor affecting wheat yield. As shown in Table 4， fertilization could significantly increase the 1 000grain weight of wheat. Compared with no fertilization， conventional fertilization increased the 1 000grain weight of wheat by 2.74%. Compared with conventional fertilization， the 1 000grain weight of wheat was increased by 2.84% in the optimized fertilization treatment. Under the same fertilization conditions， adding 3%， 4%， 5% soil improver increased the 1 000grain weight of wheat by 0.32%， 0.51%， and 3.02%， respectively from the optimized fertilization treatment. It indicated that with the increase of the application amount of soil improver， the 1 000grain weight of wheat increased. In the treatments with the same application amounts of soil improver， nitrogen reduction treatment could decrease the 1 000grain weight of wheat by 0.62%， indicting that fertilization had a certain effect on the 1 000grain weight of wheat in salinealkali soil.

In terms of wheat yield， fertilization also significantly increased wheat yield. Compared with no fertilization， conventional fertilization had the yield increased by 29.82%， and compared with conventional fertilization， optimized fertilization also increased wheat yield， indicating that scientific and reasonable nutrient distribution ratio was very necessary for crop yield. Under the same fertilization conditions， compared with optimized fertilization， wheat yield increased by 7.65%， 17.65% and 18.82%， respectively after adding 3%， 4% and 5% soil improver， indicating that wheat yield increased with the increase of the application amount of soil improver. In the treatments with the same application amount of soil improver， nitrogen reduction treatment could reduce wheat yield by 4.95%.

Conclusion

The test results showed that the application of soil improver could optimize soil aggregate structure， reduce soil bulk density， pH value and soil salt content， increase soil organic matter content， increase wheat 1 000grain weight， thereby increasing wheat yield. The increase of the application amount of soil improver could improve soil physical and chemical properties and increase crop yield， but there is no significant difference among the treatments with the application amount of 3%， 4% and 5%. Nitrogen reduction treatment showed no advantage over other treatments in soil chemical and physical properties and wheat yield， indicating that sufficient nitrogen supply is essential for the growth of wheat which has a long growth period.

Therefore， in order to further explore the effect of soil improvers， it is recommended to increase the application amount of soil improver on the premise of ensuring the supply of nitrogen fertilizer， and carry out continuous fixed point salinealkali improvement experiments for many years to verify the effects of soil improvers in a more scientific and reasonable way.

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