Effects of Fertilization on Moisture Content of Soils in the Loess Hilly-gully Region

Xuanbin XU, Zhaoliang GAO

1. State Key Laboratory of Soil Erosion and Dry Land Farming on the Loess Plateau, Institute of Soil and Water Conservation,Northwest A ＆ F University, Yangling 712100, China;

2. Soil and Water Conservation Research Institute of the University of Science and Technology, Northwest Agriculture and Forestry, Yangling 712100, China

Soil moisture is the quantity of water contained in soils, generally referring to absolute moisture content, namely, water contained in 100 g dried soils, also called soil moisture rate[1-3].Soil moisture is a key parameter of agricultural production, could be measured by weighing method, tensiometer method, resistivity method, neutron method, r-ray method, standing wave ratio, time domain reflectometry, and optical method[4]. Specifically, soil moisture rate is the proportions of water in soils,represented by θg and θv.Soil water is an important part of soils, guaranteeing plant growth and microorganism activity,as well as a key index reflecting soil quality and fertility. It is widely known that water contents have effects on plant growth, for water is necessary for material composition or decomposition, nutrient absorption and transportation, and transpiration of plants. Therefore, it is of necessity for improving soils to research soil moisture.

Simulation of Spoil Ground

Changwu County is 30.05 km of length and 27.23 km of width, totaling an area of 567.1 km2. With an altitude of 847-1 274 m, Changwu County is dominated by mountains,whose farmlands reach 20 000 hm2, and farmland per capita is few than 1 334 m2. Furthermore, it is divided into Beiyuan,Jujiayuan and Zaoyuanyuan, forming high plateau, deep valley and steep slope[5-7].In general,the county is higher in the southwest and low in northeast, which is a part of eroded Loess Plateau[8-10]. The test was located in the Changwu Agricultural Eco-experimental Station, Institute of Soil and Water Conservation,CAS&MWR,situated in Shaanxi-Gansu boundary inthe south central Loess Plateau at 107°41′E and 35°14′N. It is 200 km away from Xi’an City, and has a Warm and semi-humid continental monsoon climate.For example,annual average rainfall of reaches 584 mm,concentrated in the summer and autumn. Annual mean temperature is 9.1℃, frost-free period is 171 d, and underground water table is 50-80 m.The soils are dark loessial soils and parent materials are malan loess,performing excellently in conserving water.

Results and Analysis

Analysis on moisture contents in soil layers of 0-10 cm

As shown in Fig.1, with different fertilization methods, moisture contents of soils with varying plants were sainfoin ＞sweet clover ＞Astragalus adsurgens ＞alfalfa＞ryegrass＞coronilla varia ＞Trifolium repens, and average moisture content was 24.13%, which was 2.45%higher compared with control group.It can be concluded that almost all moisture contents in soils with the plants are higher than background value, of which the content of sainfoin was 25.31%, which was 3.63% higher compared to the control group,and the content of Trifolium repens was 22.54% , which was 0.86% higher.These indicated that the 7 crops above would all improve moisture contents,especially for sainfoin, because surface soils covered on crops would reduce water evaporation, increase rainfall infiltration, and decrease runoffs.Meanwhile, plant roots would loosen surface soils and improve water-holding capacity of soils, playing an excellent role in water conservation.

With organic fertilizer applied,moisture contents of soils with plants were as follows:sweet clover＞Coronilla varia ＞sainfoin ＞ryegrass ＞Erect milkvetch ＞Trifolium repens ＞alfalfa.Specifically, moisture content of soils with sweet clover reached the peak of 26.68%, and the lowest of alfalfa of 23.42%,which were higher by 5%and 1.74% compared with control group.Average water content was 25.56%,2.88% higher compared with control group and 1.43% higher compared with the treatment without fertilization.Except of alfalfa, moisture contents of the rest plants fertilized with organic fertilizer all increased to a certain extent compared with the treatments without fertilization, which suggested that growing plants and fertilization with organic fertilizer would significantly increase moisture content of soils,compared with single growing plants,because the application of organic fertilizer would loosen soils in different layers, promoted the absorption of rainfalls and preventing rainfall runoffs.

In the treatment with straws, soil moisture contents from high to low were as follows: Trifolium repens ＞sainfoin ＞alfalfa ＞ryegrass ＞Erect milkvetch＞Melilotus suavcolen＞Coronilla varia,and average moisture content was 20.37%, which lowered by 5.19% and 3.76% compared with the treatments with organic fertilizer and the treatment without fertilizers, and was 1.31% lower compared with control group. In the treatment applied with straws, the moisture content reached the peak of Trifolium repens at 22.88%, which reduced by 1.53%compared with the treatment with organic fertilizer, and was slightly higher compared with the treatment without fertilizers(22.54%).The moisture content of soils with Coronilla varia was the least at 18.03%, which was significantly lower compared with rest treatments. Fig.1 showed that, moisture contents of soils applied with different plants was lowercompared with the former treatments, possibly caused by large consumption of water from straw decomposition.

Analysis on moisture contents in soil layers of 10-20 cm

As shown in Fig.2, in the treatment without fertilizers, moisture content of soils with Melilotus suavcolen was the highest at 24.36%,which was 2.62% higher compared with control group, and moisture content of soils with ryegrass was 22.18%, which was 0.44% higher compared with control group. The moisture contents were as follows: Melilotus suavcolen＞Trifolium repens ＞Astragalus adsurgens ＞Coronilla varia ＞sainfoin＞alfalfa＞ryegrass;the moisture content averaged 23.12% , which was 1.38% higher compared with control group, and 1.01% lower compared with the same treatment with soils of 0-10 cm; except of Trifolium repens, moisture contents of soils of 10-20 cm soil layer maintained lower compared with soils of 0-10 cm in the treatment without fertilizers,but still kept higher than that of control group. These indicated that all of the plants would increase moisture content of soils in the 0-20 cm soil layers,but the increase performed bet-ter in surface soils.

In the treatment with organic fertilizer, moisture content of soils with Coronilla varia was the highest of 27.16%,which was a little higher compared with soils of 0-10 cm and 5.42%higher compared with control group;the moisture content of soils with alfalfa was the lowest of 22.50%, which was similar to the soils of 0-10 cm layer. These suggested alfalfa performed the worst in improving soil moisture. Furthermore, in the treatment, moisture contents of soils of 10-20 cm were as follows: Coronilla varia ＞ryegrass ＞Melilotus suavcolen ＞Astragalus adsurgens ＞Trifolium repens ＞sainfoin ＞alfalfa; moisture content averaged 24.14%, which was 1.02% higher compared with the treatment without fertilizer and 2.4%higher compared with control group,but 1.42% lower compared with the treatment with organic fertilizers of soils of 0-10 cm.The research indicated that application of organic fertilizer increased moisture content of surface soils.

Among the treatments with straws, the rate of soil moisture in soil layers of 10-20 cm layer was lower compared with rest treatments and maximal moisture rate reached the peak of 22.95 with soils grown with Trifolium repens,which was 1.21%higher compared with control group, and 4.41% and 4.21% lower compared with maximums in treatments without fertilizers and with organic fertilizer,respectively.The moisture rate of soils with Melilotus suavcolen was the lowest (19.36%),2.38%lower compared with control group. Specifically, moisture rates of soils with plants followed as: Trifolium repens ＞Coronilla varia ＞Astragalus adsurgens＞ryegrass＞sainfoin＞alfalfa ＞Melilotus suavcolen, and average moisture rate was 21.39%,which reduced by 2.75% and 1.73%compared with the treatment with organic fertilizer and the treatment without fertilizers, and .35% lower compared with control group. In the treatment, the rate of soil moisture of 10-20 cm layer still kept lower compared with rest treatments, possibly caused by water consumption during straw decomposition.

Conclusions and Discussions

The research indicated that for soils grown with different plants, the rate of moisture of soils in 0-20 cm would be improved in the treatments with or without fertilizers,application of organic fertilizer and growing plants would enhance soil moisture, reduce moisture loss of soil and improve water supply of soil, and improve soil fertility., average moisture rate in the 0-10 cm layer in the treatment without fertilizer proved 2.45% higher than that of control group and the treatment with fertilizer was 3.88% higher. average moisture rate in the 10-20 cm layer in the treatment without fertilizer proved 1.38%higher than that of control group and the treatment with fertilizer was 2.4% higher. However, the effect of treatment with organic fertilizer performed better.For example,the rate of moisture was 1.43% higher in the treatment with organic fertilizer of soils in 0-10 cm, and 1.02% higher of soils in 10-20 cm soil layer. The decrease of soil moisture in the treatment with straws is possibly due to water consumption from straw decomposition.

Therefore, soil moisture would decline by the application of straws at early stage, which coincides with previous researches. Nevertheless, similar researches demonstrated that after straw decomposition, volume weight and porosity of soil can improve, and organic matter and nutrients of soils increase, which benefit the improvement ofsoil moisture. Specifically, average moisture rate of soils in the0-10 cm layer was higher compared with soils in 10-20 cm soil layer, proved that moisture content significantly increased in the surface soils.

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