Effects of Irrigation Amount on Soil Water Content of Gentiana macrophylla

Xiaojun WANG, Xinxue ZHANG, Hua LIU

Abstract [Objectives] This study was conducted to investigate the effects of different irrigation quotas and irrigation times on soil physical and chemical properties and water content in the planting areas of Gentiana macrophylla in dry farming areas of southern Ningxia.

[Methods]G. macrophylla planted for three years was selected as the experimental material， and the water content， nutrients， bulk density and total porosity of the soil at different depths （0-20 and 20-40 cm） were measured under different irrigation quotas and irrigation times.

[Results] Compared with the CK， different irrigation quotas and irrigation times could significantly improve the water contents of the 0-20 and 20-40 cm layers in the planting areas of G. macrophylla. The change trend of water content at the 0-20 cm soil depth was 3 times of irrigation>2 times of irrigation>1 time of irrigation>CK， and that at the 20-40 cm soil depth was 2 times of irrigation>3 times of irrigation>1 time of irrigation>CK. With the increase of irrigation times， soil urease in the 0-20 cm soil showed a trend of decreasing at first and then increasing， reaching a maximum value of 0.415 mg/g·24 h with 1 time of irrigation， which increased by 84.44% compared with the CK， and the value with two times of irrigation was basically the same as that of the CK， but 3 times of irrigation resulted in a value 57.33% higher than the CK. However， the changes of 20-40 cm were the opposite. The change trends of alkali-hydrolyzable nitrogen in the 0-20 and 20-40 cm soil layers with irrigation times was smaller， and the contents of soil organic carbon， available phosphorus and available potassium increased first and then decreased with the increase of irrigation times， and were generally higher than those in the CK.

[Conclusions]This study provides a theoretical and technical basis for the artificial cultivation of G. macrophylla in dry farming areas of Ningxia.

Key words Irrigation quota; Irrigation times; Water content; Effect

Received： February 16， 2022  Accepted： April 18， 2022

Supported by Collection of Gentiana macrophylla Germplasm Resources in Imitated Wild Conditions under Forests in Liupan Mountains and High-yield Cultivation Technology （2020GYKYF011）; Sub-project of Scientific and Technological Innovation Demonstration Project for High-quality Agricultural Development and Ecological Protection in Ningxia Hui Autonomous Region （NGSB-2021-16-05）.

Xiaojun WANG （1983-）， male， P. R. China， research assistant， master， devoted to research about plant nutrition and formula fertilization by soil testing.

*Corresponding author.

Rainfall is scarce in the mountainous areas of southern Ningxia， where the average annual effective rainfall is only 300-320 mm and the soil organic matter content is low[1]. Therefore， the shortage of water resources has become the main limiting factor for the development of agricultural production and ecological environment construction in Ningxia[2]. In order to meet the ever-increasing demand of Gentiana macrophylla in the Chinese herbal medicine market， people are increasingly serious about the development of G. macrophylla resources. It has become the primary choice to develop the Chinese herbal medicine industry in Ningxia according to local conditions， improve local ecological environment， and increase local farmers income. However， due to the backward artificial cultivation technology of G. macrophylla and low soil fertility and drought in the planting area， the development of Chinese herbal medicine industry has been seriously affected. Drip irrigation is mainly concentrated on the production of major cash crops in water-scarce areas[3-7]. For example， drip irrigation under film for maize is 18% more efficient than ground flood irrigation[8]. Relevant studies have shown that 5 times of irrigation during the whole growth period of winter wheat with an irrigation quota of 365 mm was the best[9]. Zhang[10] studied that the yield of winter wheat in arid areas of Xinjiang reached the highest when the drip irrigation quota was 375 mm. Song et al.[11] investigated the effects of the coupling of irrigation amount and nitrogen application rate on the growth and yield of wolfberry. The results showed that implementing a certain degree of adjusted deficit irrigation and nitrogen-reduced fertilization could increase the yield and income of wolfberry. Therefore， a reasonable amount of irrigation will not only improve crop yield， but also improve water use efficiency. There are very few reports on the effects of different irrigation amounts on soil nutrients. Relevant studies have shown that high-volume irrigation can lead to the leaching of soil nitrate nitrogen， resulting in crop yield reduction[12]. Appropriately increasing phosphorus fertilizer and controlling the amount of irrigation can effectively prevent phosphorus leaching[13]. Therefore， the changes of soil physical and chemical properties and water content of G. macrophylla with different irrigation amounts were analyzed to explore the reasonable irrigation amount and nutrient scientific management of G. macrophylla. This study provides a theoretical and technical basis for the artificial cultivation of G. macrophylla in dry farming areas of Ningxia.

Basic Situation of the Experimental Site

The experimental site is 1 550 m above sea level， 36°44′27″ north latitude and 106°43′26″ east longitude. This area has dry winter， and the four seasons are windy; the precipitation is generally concentrated in July to September; the annual evaporation is 1 650 mm; and the accumulated temperature≥10 ℃ is 2 800 to 3 500 ℃; and the annual frost-free period is 150 to 200 d. The soil belongs to Hunan loess. The physical and chemical properties of the tested soil （0-40 cm） were as follows： available phosphorus content 38.5 mg/kg， available potassium content 168 mg/kg， organic matter content 7.38 g/kg， alkali-hydrolyzable nitrogen content 66.0 mg/kg， total nitrogen content  0.61 g/kg， total phosphorus content 0.79 g/kg， total potassium content 14.6 g/kg， and pH value 8.43. The rainfall and temperature conditions in the third consecutive year for the growth of G. macrophylla are shown in Fig. 1.

Experimental Methods

The designed irrigation quotas were 400， 500 and 600 m3/hm2， and the irrigation times were 1， 2， and 3 times during the whole growth period of G. macrophylla， respectively. No irrigation was used as the control check （CK）. The area of each experimental plot was 15 m2， and each treatment was done in triplicate. The irrigation time was March 10， May 9， and July 8. The experimental period was 3 years.

In order to prevent mutual penetration between the plots， a black film with a depth of 2 m and a thickness of 0.5 mm was buried in each plot at the beginning of the experiment. The experiment adopted the methods of pump drip irrigation and water meter measurement， and other field management measures were the same as those in the field.

The first water irrigation was carried out on March 10 every year. The water of the 0-20 and 20-40 cm soil of each treatment were collected every 15 d， and the soil water contents were calculated by the TDR and drying methods. And， the mean value of 3 replicates was taken.

Results and Analysis

Effects of different irrigation times on the water content of the 0-20 cm soil

From Fig. 2， Fig. 3 and Fig. 4， it can be seen that irrigation could effectively increase soil water content and rapidly increase soil water content in a short period of time. However， with the extension of time， the soil water content gradually decreased and gradually became stable under the state of absorption and utilization by plants and soil and natural evaporation. The soil water content curves fully showed that with certain irrigation amount， the frequency of irrigation had a significant effect on the water content of the 0-20 cm soil in arid areas， and the soil water contents were all higher than that of the CK， indicating that irrigation caused a significant increase in the soil water content of 0-20 cm. However， in the later period of irrigation， the soil water contents were basically the same as that of the CK.

Effects of different irrigation times on the water content of the 20-40 cm soil

From Fig. 5， Fig. 6 and Fig. 7， it can be seen that irrigation could also effectively increase the soil water content in the 20-40 cm soil， and the soil water content increased rapidly in a short period of time. With the passage of time after irrigation， the absorption and utilization of water by plants and soil and the state of natural evaporation， the rate of decline was slow with the irrigation quotas of 400 and 500 m3/hm2， and the minimum water content of irrigated soil was higher than that of the CK overall， while the soil water content decreased rapidly and the minimum soil water

content was basically the same as the CK， with the irrigation quota of 600 m3/hm2. It showed that in the dry months， the frequency of irrigation had a certain effect on the water content of the 20-40 cm soil， and it played a role in retaining water in the treatments of 400 and 500 m3/hm2. The main reason might be that affected by the type of crop， external factors， especially artificial weeding， had less disturbance to the 20-40 cm ploughing layer.

Effects of different irrigation quotas on the water content of the 0-20 cm soil

Fig. 8， Fig. 9 and Fig. 10 respectively show the changes of soil water content in the 0-20 cm layer with different irrigation quotas under the same irrigation times.

It can be seen from Fig. 8 that under one time of irrigation， the variation trend of soil water content with the irrigation quotas of 400， 500 and 600 m3 was 600 m3>500 m3>400 m3>CK.

Fig. 8 shows that under two times of irrigation， the variation trend of soil water content with the irrigation quotas of 400， 500 and 600 m3 was 500 m3> 600 m3>400 m3>CK.

It can be observed from Fig. 10 that under three times of irrigation， the variation trend of soil water content with the irrigation quotas of 400， 500 and 600 m3 was 500 m3> 600 m3>400 m3>CK.

The water change curves showed that the soil water contents of the irrigation treatments were significantly higher than that of the CK， and the soil water contents also showed a downward trend in the later period of irrigation with the passage of time. Meanwhile， the overall changing trend of soil water content with different irrigation quotas was 3 times of irrigation>2 times of irrigation>1 time of irrigation>CK， and there were no significant differences between different irrigation times. It indicated that increasing the frequency of irrigation did not significantly increase the water content of the 0-20 cm soil in the dry period.

Effects of different irrigation quotas on the water content of the 20-40 cm soil

Fig. 11， Fig. 12 and Fig. 13 respectively show the changes of water content in the 20-40 cm soil with different irrigation quotas under the same irrigation times.

It can be seen from Fig. 11 that under one time of irrigation， the variation trend of soil water content with the irrigation quotas of 400， 500 and 600 m3 was 600 m3>500 m3>400 m3>CK.

Fig. 12 exhibits that under two times of irrigation， the variation trend of soil water content with the irrigation quotas of 400， 500 and 600 m3 was 400 m3>500 m3> 600 m3>CK.

It can be observed from Fig. 13 that under three times of irrigation， the variation trend of soil water content with the irrigation quotas of 400， 500 and 600 m3 was 600 m3> 500 m3>400 m3>CK.

The water change curves showed that the soil water contents of the irrigation treatments were significantly higher than that of the CK. Similar to the changes of soil water content in the 0-20 cm layer， the soil water content also showed a rapid decline trend in the later period of irrigation with the advancement of time. The changing trend of soil water content with different irrigation quotas was 2 times of irrigation>3 times of irrigation>1 time of irrigation>CK， and there were significant differences between different irrigation times. It indicated that the frequency of irrigation had a great effect on the change of the water content in the 20-40 cm soil.

Conclusions and Discussion

Field soil has great variability， and soil water content is significantly affected by factors such as precipitation and irrigation. Irrigation can effectively adjust soil water and nutrients[14]. Guo[15] showed that a large amount of irrigation would increase the migration of water to the deep soil layer and reduce the water use efficiency. In this study， the soil water content in the treatments with the irrigation quota of 600 m3/hm2 decreased rapidly and the minimum soil water content was basically the same as that of the CK， while the 400 and 500 m3/hm2 treatments had the function of retaining water. Some studies have pointed out that under drip irrigation conditions， the soil moisture in the 0-20 cm soil layer was higher[16] or the soil moisture content in the 0-30 cm soil layer at the roots significantly increased[17-18]. In this study， irrigation could effectively increase the water content of the 0-20 cm soil， and the increase was faster than the water content of the 20-40 cm soil， but with the passage of time after irrigation， the soil water content decreased rapidly and became stable gradually， which was mainly because that the annual effective rainfall was less and the evaporation was large in the year of the experiment. However， different irrigation quotas could significantly increase the water content of the 0-20 cm layer under the same irrigation times， and the variation trend of soil water content was 3 times of irrigation>2 times of irrigation>1 time of irrigation>CK. Therefore， the frequency of irrigation and the amount of irrigation can effectively adjust water distribution.

Soil physical and chemical properties are comprehensively affected by many factors， such as rainfall， crop water absorption， soil porosity， and irrigation and fertilization modes， while G. macrophylla is a perennial plant with rhizomes used as a Chinese herbal medicine， and its roots are mainly concentrated above the 40 cm soil layer. The migration of fertilizers into the soil varies greatly due to the absorption of roots and the effect of soil on the migration and diffusion of nutrients. In this study， the number of irrigation times affected soil bulk density and clay particles at different soil depths. Irrigation times can also make soil enzyme activity and nutrient content show different trends with the increase of irrigation times. This study also showed that urease， catalase and sucrase showed a fluctuating trend under different irrigation treatments. The 0-20 cm soil alkali-hydrolyzable nitrogen also changed with irrigation frequency， and soil organic carbon and available phosphorus increased first and then decreased with the increase of irrigation frequency. Studies have shown that irrigation can significantly affect the changes of soil alkali-hydrolyzable nitrogen content and available phosphorus content[19-20]， which is basically consistent with the results of this study. Relevant studies have shown that the content of soil available potassium varies greatly at different levels under different irrigation quotas， but it has less impact on crops with planting depths below 40 cm[21]. In this study， 3 times of irrigation led to a higher content of available potassium in the soil of 0-20 cm， while the effect was less in the soil layer of 20-40 cm， indicating that the times of irrigation could directly affect the migration of available potassium.

References

[1] MA YL. Soil testing and formula fertilization technology in Ningxia[M]. Yinchuan： Ningxia peoples Publishing House， 2005： 171-179. （in Chinese）.

[2] DUAN AW， XIN NQ， WANG LX. Exploitation of water-saving potential in irrigation agriculture in Northwest China[J]. Review of China Agricultural Science and Technology， 2002， 4（4）： 50-55. （in Chinese）.

[3] ZHANG ML. Research on the application of water and fertilizer integrated drip irrigation technology in facility vegetables[J]. Agriculture & Technology， 2018， 38（21）： 113-114. （in Chinese）.

[4] HAN Y， ZHANG HM， SONG YP， et al. Research progress and development trend of water and fertilizer integrated equipment in orchards at home and abroad[J]. Journal of Chinese Agricultural Mechanization， 2020， 41（08）： 191-195. （in Chinese）.

[5] LIU Y， LI YF， LI JS， et al. Effects of mulched drip irrigation on water and heat conditions in field and maize yield in sub-humid region of Northeast China[J]. Transactions of the Chinese Society for Agricultural Machinery， 2015， 46（10）： 93-104，135. （in Chinese）.

[6] NIE ZJ， CHEN YQ， ZHANG JS， et al. Effects of drip irrigation patterns on wheat yield and water use efficiency in Heilonggang region[J]. Acta Agronomica Sinica， 2013， 39（09）： 1687-1692. （in Chinese）.

[7] XUE LH， ZHAO LJ， CHEN XW， et al. Effects of different water and nitrogen application patterns on the growth of root and yield of winter wheat[J]. Journal of China Agricultural University， 2017， 22（09）： 21-31. （in Chinese）.

[8] ZHAO LJ， XUE LH， SUN QK， et al. Effect of different irrigation and nitrogen application on water consumption characteristics and the water and nitrogen use efficiencies under drip irrigation in winter wheat[J]. Journal of Triticeae Crops， 2016， 36（08）： 1050-1059. （in Chinese）.

[9] CHEN J， WANG YC， LI H， et al. Effects of drip fertigation with no-tillage on water use efficiency and yield of winter wheat [J]. Scientia Agricultura Sinica， 2014， 47（10）： 1966-1975. （in Chinese）.

[10] ZHANG N， ZHANG YQ， XU WX， et al. Effect of different drip irrigation amounts on microclimate and yield of winter wheat[J]. Chinese Journal of Eco-Agriculture， 2016， 24（01）： 64-73. （in Chinese）.

[11] SONG YC， CHEN XL， REN XL， et al. Combined effects of regulated deficit irrigation and reduced nitrogen fertilization on yield and growth of Chinese wolfberry[J]. Acta Agriculturae Boreali-occidentalis Sinica， 2019， 28（10）： 1666-1673. （in Chinese）.

[12] ZHANG SL， TONG YA， LIANG DL， et al. Nitrate-N movement in the soil profile as influenced by rate and timing of nitrogen application [J]. Acta Pedologica Sinica， 2004， 41（2）： 270-277. （in Chinese）.

[13] XIANG DL， YANG XY， SUN BH， et al. Impacts of irrigation regimes on phosphorus leaching in manural loessial soil[J]. Journal of Plant Nutrition and Fertilizer， 2016， 16（1）： 112-117. （in Chinese）.

[14] WANG C， LI YN. Laboratory experimental study on soil-water movement of subsurface drip irrigation[J]. Journal of Irrigation and Drainage， 2011， 30（1）： 136-138. （in Chinese）.

[15] GUO QZ. Effect of different irrigation amount on the moving of soil water and nutrient in soil profiles of tomato greenhouses[J]. Acta Agriculturae Boreali-occidentalis Sinica， 2013， 22（4）： 153-158. （in Chinese）.

[16] LIU XL， CAI T， XU Y， et al. Effect of limited water-saving irrigation on winter wheat water use efficiency and yield in Guanzhong irrigation district[J]. Water Saving Irrigation， 2018（01）： 24-29. （in Chinese）.

[17] LYU LH， HU YK， LI YM， et al. Effect of irrigating treatments on water use efficiency and yield of different wheat cultivars[J]. Journal of Triticeae Crops， 2007， 27（1）： 88-92. （in Chinese）.

[18] FU WH， JIANG RF， LIU QQ， et al. Influence of different irrigation technology on production of winter wheat in north plain[J]. Acta Agriculturae Boreali-Sinica， 2013， 28（02）： 175-179. （in Chinese）.

[19] ZHU JR， YANG T， WANG B， et al. Sectional distribution of alkaline-hydroluzale nitrogen of cotton field soil under different irrigation water supply in arid area[J]. Xinjiang Agricultural Sciences， 2011， 48（4）： 696-701. （in Chinese）.

[20] WANG YS， ZHANG YL， YU N， et al. Effect of control lower limit of subsurface irrigation on phosphorus distribution in soil profiles of protected land[J]. Transactions of the Chinese Society of Agricultural Engineering， 2009， 25（6）： 66-70. （in Chinese）.

[21] FENG XM， FAN GS. Effects of fast-available potassium in soil after irrigation with spate[J]. Journal of Taiyuan University of Technology： Social Sciences Edition， 2006， 37（2）： 209-212. （in Chinese）.