Nutrient Accumulation Characteristics of Facility Soils with Different Planting Years in Lateritic Red Soil Region of Guangxi

Guifen CHEN, Yanfei HUANG, Mei PANG, Yuyi HUANG*, Bin LIU, Xiuhe ZHAO, Xiaoqing OU, Yueyue ZHOU, Liumei XIONG

1. Agricultural Resource and Environment Research Institute, Guangxi Academy of Agricultural Sciences, Nanning 530007, China; 2. Agricultural Research Institute of Beihai, Beihai 536000, China

Abstract [Objectives] To explore the nutrient accumulation characteristics of facility soil in different planting years in the lateritic red soil region of Guangxi. [Methods] The soil samples of facility cultivation and open field cultivation were collected in the lateritic red soil region of Guangxi, and the changes of soil pH, water-soluble salts, organic matter, available nutrients and total nutrients were analyzed. [Results] The acidification of the facility soil in the lateritic red soil region of Guangxi became more obvious with the extension of greenhouse planting years, the soil pH decreased by 0.34 units after continuous planting for 10 years, and the water-soluble content was more than 3 times that of the open field and it increased with the extension of the planting years. In addition, the degree of secondary salinization in facility soil became more serious, mainly moderate and mild salinization. The contents of soil organic matter, alkali-hydrolyzed nitrogen, available phosphorus, available potassium, total nitrogen and total phosphorus in the facility soil increased significantly, while total potassium did not change significantly. [Conclusions] This study is expected to provide a scientific basis for facility soil fertilization management, and to promote the sustainable and healthy development of facility cultivation industry.

Key words Facility soil, Planting years, Nutrient accumulation, Acidification, Salinization

1 Introduction

Facility agriculture is an important industry for farmers to increase production and income. Facility cultivation, as a modern agricultural technology, has characteristics of high resource utilization efficiency, easy to achieve high and stable crop yield, and significant economic benefits. With the requirements of modern agricultural development and the needs of agricultural industrial structure adjustment and supply-side reform, facility agriculture has developed rapidly in China in recent years. At present, China ranks first in the world in the facility cultivation area and the total output of agricultural products, and the facility cultivation area in Guangxi is up to 40 000 ha. The input of organic fertilizers and chemical fertilizers in facility cultivation production is much higher than that in the open field production. In addition, due to the high multiple cropping index, long-term high temperature and high humidity conditions, and lack of precipitation leaching, the facility soil is more prone to nutrient enrichment, soil acidification and salinization[1]. With the increase of planting years, the problems of soil secondary salinization, acidification, nutrient imbalance, soil compaction, and frequent occurrence of pests and diseases have become more and more serious[2-3]. In recent years, extensive studies have been carried out on the degradation problems of facility soil, such as the accumulation of nutrients, secondary salinization, and the composition of water-soluble salt ions[4-6]. However, there are few studies about the research on the soil nutrient status of the facilities in the lateritic red soil region of Guangxi, and there is a lack of targeted research. In this situation, taking the facility soil of the lateritic red soil region in Guangxi as the research object, we explored the characteristics of facility soil nutrient accumulation in different planting years, to provide a scientific basis for facility soil fertilization management, and to promote the sustainable and healthy development of facility cultivation industry.

2 Materials and methods

2.1 Soil sample collectionDuring January 2019 to March 2021, we collected soil samples in greenhouses and multi-span greenhouses with different planting years (1-5 years, 6-10 years and more than 11 years) in the lateritic red soil region of Guangxi. The sampling depth was 0-20 cm, and one soil sample represents a mixed sample with an area of 667-2 000 m2in a greenhouse or a multi-span greenhouse. Each greenhouse soil sample was collected from multiple points, and the sampling points were distributed in the "S" shape. Using a stainless steel shovel or a stainless steel soil drill, 5-10 soil sample points of the tillage layer were randomly collected. After fully mixing, 1 kg samples were set aside by the quartering method, put into a polyethylene plastic bag, marked and sealed. Besides, the same method was used to collect soil samples from open field planting near the greenhouse as a control. The samples were brought back to the laboratory for air-drying, ground and sieved according to the requirements of the analysis items, and then bottled for later use. A total of 77 soil samples were collected, including 23 samples with 1-5 planting years, 17 samples with 6-10 planting years, 17 samples with more than 11 planting years, and 20 samples planted in the open field.

2.2 Test items and methodsThe soil pH was tested using an acidity meter (soil-water ratio 1∶5); water-soluble salt was tested using the mass method (soil-water ratio 1∶5); the alkaline hydrolysis nitrogen was tested using the the alkaline hydrolysis diffusion method; the available phosphorus was extracted by 0.5 mol/L extraction NaHCO3-molybdenum-antimony anti-colorimetric method; the available potassium was extracted by NH4OAc-flame photometer method; the organic matter content was determined by the potassium dichromate volumetric method; the total nitrogen was determined using Kjeldahl method; the total phosphorus was determined using the sodium hydroxide fusion-molybdenum antimony anti-colorimetric method; the total potassium was determined using the sodium hydroxide fusion-flame photometer method.

2.3 Statistical analysis of dataThe experimental data were statistically analyzed using Excel 2007.

3 Results and analysis

3.1 Characteristics of changes in pH and water-soluble salt content in facility soil with different planting yearsSoil pH is an important indicator of basic soil properties. The pH has a great influence on the form and availability of soil nutrients, physical and chemical properties of soil, microbial activity and plant growth. The salt content of soil, if accumulated to a certain concentration, will also affect plant growth and development. As shown in Table 1, the average pH of the facility soil with different planting years was lower than that of the open field soil, and it showed a gradual decline trend with the increase of the greenhouse planting years. In addition, the proportion of acidic soil samples also increased. After 10 years of greenhouse cultivation, the pH dropped by 0.34 units, and the proportion of soil samples with pH lower than 5.5 increased from 50% to 58.82%, indicating that the soil in the lateritic red soil region of Guangxi facility showed a trend of acidification with the increase of the greenhouse planting years. The water-soluble salt content of facility soil was higher than that of open-field soil, and showed a rising trend with the increase of greenhouse planting years. The water-soluble salt content of the facility soil with 1-5, 6-10 years and more than 11 planting was 3.11, 3.34 and 3.63 times that of the open field soil, respectively. The proportion of salinized soil also showed an increasing trend, indicating that the degree of secondary salinization of facility soil increased with the increase of planting years, and was mainly moderate and mild salinization.

3.2 Characteristics of changes in organic matter content in facility soil with different planting yearsSoil organic matter is an important indicator for evaluating soil fertility, and it is a key factor influencing physical and chemical properties such as soil structure, soil buffer performance, water retention and fertilizer supply performance, nutrient availability, and soil aeration. As shown in Table 2, the organic matter content of the facility soil was higher than that of the open field soil, and it continued to accumulate with the increase of greenhouse planting years. The soil organic matter content of the greenhouse planting years of 1-5, 6-10 and more than 11 years was 34.38%, 76.51% and 86.94%, respectively higher than that of the open field soil, and the proportion in the extremely rich level also increased from 15.0% in the open field to 17.39%, 23.53% and 47.06%, respectively.

Table 1 The pH and water-soluble salt content in facility soil with different planting years

Table 2 Organic matter content in facility soil with different planting years

3.3 Characteristics of changes in available nutrient content in facility soil with different planting yearsFrom Table 3, it can be known that the contents of alkaline-hydrolyzed nitrogen, available phosphorus and available potassium in the facility soil were significantly higher than those in the open field. Alkali-hydrolyzable nitrogen did not change significantly with the increase of greenhouse planting years. The content of alkaline-hydrolyzable nitrogen in facility soil with 1-5, 6-10 and more than 11 planting years was 2.04, 1.98 and 2.08 times that of open field soil, respectively. The highest proportion of samples with extremely high content levels was 6-10 planting years, accounting for 94.12%, followed by more than 11 planting years, accounting for 88.24%, and 1-5 planting years also accounting for 78.26%. The content of available phosphorus continued to accumulate with the increase of greenhouse planting years. The content of available phosphorus in facility soil with 1-5, 6-10 and more than 11 planting years was 2.58, 4.04 and 4.53 times that of open field soil, respectively. Most samples were at extremely high level. The content of available potassium also continued to accumulate with the increase of greenhouse planting years. The content of available potassium in facility soil with 1-5, 6-10 and more than 11 planting years was 2.24, 2.42 and 2.97 times that of open field soil, respectively. The proportion of samples at extremely high level also increased with the planting years.

Table 3 Available nutrient content in facility soil with different planting years

3.4 Characteristics of changes in total element content in facility soil with different planting yearsAs shown in Table 4, the total nitrogen content of the facility soil with different planting years was higher than that of the open field soil, and it continued to increase with the increase of greenhouse planting years. The total nitrogen content of facility soil with 1-5, 6-10 and 11 planting years was higher than that of the open field soil by 44.75% and 67.83% and 75.52%, respectively. The change trend of total phosphorus content in facility soil with different planting years was basically consistent with the change trend of total nitrogen content. The total phosphorus content increased with the increase of the greenhouse planting years. Since phosphorus is easier to be adsorbed and fixed in the soil, its accumulation increased greatly. The total phosphorus content of facility soil with 1-5, 6-10 and more than 11 planting years increased by 67.59%, 164.81% and 231.48% respectively compared with the open field soil. However, there was no obvious rule in the change of total potassium content in facility soil with different planting years. The total potassium content of facility soil with 1-5 planting years was 38.75% higher than that of open field soil, while the total potassium content of facility soil with 6-10 planting years and more than 11 years was lower than that of open field soil, possibly because the total potassium content of the facility soil mainly depends on the potassium content in the soil parent material, and has little to do with the greenhouse planting years.

Table 4 Total element content in facility soil with different planting years

4 Discussion

The contents of organic matter and soil nutrients (except total potassium) in the facility soil were generally higher than those in the open field soil. The high content of soil organic matter was mainly due to the accumulation of organic matter on the soil surface due to the long-term application of organic fertilizers and the return of crop straws to the field. In addition, the degradation rate was lower than the application rate, resulting in gradual increase in organic matter content. The level of alkali-hydrolyzed nitrogen content can reflect the ability of the facility soil to supply nitrogen to crops. On the whole, the alkali-hydrolyzed nitrogen content of facility soil was higher than that of open field soil, but there was no significant change with the increase of greenhouse planting years. The total nitrogen content showed an increasing trend with the extension of greenhouse planting years, possibly because the accumulation of nitrogen on the soil surface caused by the long-term blind application of nitrogen fertilizer by farmers in pursuit of high yield, and its degradation rate was lower than the rate of fertilization. The content of available phosphorus and total phosphorus in the facility soil was relatively rich and accumulated year by year. Excessive application of phosphorus fertilizer by farmers caused phosphorus to accumulate on the soil surface. At the same time, phosphorus may form relatively stable complexes with organic matter and remain in the soil, so that phosphorus was enriched in the soil, and the soil phosphorus content was too high. This may lead to unbalanced crop nutrients, low fertilizer utilization rate and other consequences, and may also enter the water body and cause the eutrophication of the water body to deteriorate the ecological environment. In the process of production, it is necessary to take certain measures to control the application amount of phosphorus fertilizers to prevent excessive phosphorus content in the soil from causing phosphorus enrichment and influencing crop yield and quality. Too high content of available potassium in the facility soil is mainly because the "potassium supplementation project" advocated in China in recent years, the excessive application of potassium fertilizer by farmers has increased the concentration of potassium ions in the soil. Although some crops require a large amount of potassium during the growth process, farmers rarely consider the actual effective potassium content in their greenhouse soil and blindly apply a large amount of potassium fertilizer. This not only causes the enrichment of potassium in the soil, but also causes the waste of resources. The total potassium content of the facility soil has little to do with the greenhouse planting years, and the total potassium content of the soil may mainly depend on the potassium content of the soil parent material. According to the results of this study, the content of available phosphorus and available potassium in all greenhouses in the sampling area has exceeded the abundant level. It is necessary to strictly control the application amount of phosphorus and potassium fertilizers to avoid adverse effects on crops due to excessive content. At present, the main problems in greenhouse cultivation in China are unreasonable fertilization, excessive or insufficient fertilization, and single variety. The most important reason is that farmers cannot determine the variety and amount of fertilizers to be applied according to the specific physical and chemical properties of the greenhouse soil and the cultivated plants, and cannot achieve "fertilization in accordance with soil conditions". In addition, farmers do not have sufficient theoretical knowledge of fertilization, and their awareness of using modern science and technology to increase crop production and income is insufficient. In consequence, the nutrients contained in the soil are unbalanced, which has a certain impact on the growth of crops.

5 Conclusions

(i) The facility soil acidification in lateritic red soil region of Guangxi became more obvious with the extension of greenhouse planting years. The soil pH dropped by 0.34 units after 10 years of continuous planting.

(ii) The water-soluble content was more than 3 times that of the open field and it increased with the extension of the planting years. In addition, the degree of secondary salinization in facility soil became more serious, mainly moderate and mild salinization. The contents of soil organic matter, alkali-hydrolyzed nitrogen, available phosphorus, available potassium, total nitrogen and total phosphorus in the facility soil increased significantly, while total potassium did not change significantly.

(iii) The nutrient content of the facility soil was generally accumulated year by year with the extension of the planting years, especially the accumulation of phosphorus has a greater increase. In the process of production, it is necessary to take certain measures to control the application amount of phosphorus fertilizers to prevent excessive phosphorus content in the soil from causing phosphorus enrichment and influencing crop yield and quality.