Effects of Tillage Methods on Soil Available Phosphorus and Available Potassium in the Loess Plateau

Shaanxi Provincial Land Engineering Construction Group Co., Ltd., Xi’an 710075, China; Institute of Shaanxi Land Engineering Construction Group Co., Ltd., Xi’an 710075, China; Key Laboratory of Degraded and Unused Land Consolidation Engineering, Ministry of Land and Resources, Xi’an 710075, China; Shaanxi Provincial Land Consolidation Engineering Technology Research Center, Xi’an 710075, China

Abstract In order to find out the effects of long-term no-tillage operation on soil available phosphorus and available potassium in the loess plateau, a suitable high-yield and high-efficiency tillage technology system was established. In the Changwu loess plateau agri-ecological experiment station of the Northwest A&F University of Changwu County, Shaanxi Province, the no-tillage experimental field for three consecutive years was selected. In September 2015, no-tillage, tillage, and rotary tillage were carried out before winter wheat was sowed. After the harvest of winter wheat in 2016, the contents of available phosphorus and available potassium in 0-30 cm soil layer under three tillage methods were analyzed. The results showed that in the 0-30 cm soil layer, the soil available phosphorus and available potassium decreased with the increase of the soil depth in the three tillage methods. The content of available phosphorus and available potassium in 10-20 cm soil layer and 20-30 cm soil layer decreased by 16.07%, 32.74%, 15.54% and 27.08%, respectively, and there were significant differences (P<0.05). Under different tillage methods, the soil available phosphorus content in the 0-10 cm soil layer significantly reduced by 11.31% compared with no-tillage. The soil available potassium content under tillage and rotary tillage significantly reduced by 6.16% and 4.97%, respectively (P<0.05). Compared with no-tillage, the soil available phosphorus content in the 20-30 cm soil layer significantly reduced by 18.12%. The soil available potassium content under tillage and rotary tillage methods significantly reduced by 17.17% and 9.22%, respectively (P<0.05). Therefore, in the long-term no-tillage dry loess plateau, it is necessary to conduct proper tillage or rotary tillage.

Key words Tillage methods, Available phosphorus, Available potassium, Dry loess plateau

1 Introduction

Soil is the foundation for the survival of crops. Different tillage method of soil is an essential research content in agricultural production technology system[1]. Selecting an appropriate tillage method has a positive effect on soil nutrient fixation, crop growth and yield formation[2-4]. Compared with the traditional tillage, in recent years, there gradually appear protective tillage technologies such as no-tillage and subsoiling[5-6]. Extensive research results both at home and abroad have shown that such protective tillage methods such as no-tillage and less tillage can reduce the wind erosion and alleviate water erosion, improve the soil physical and chemical properties, and also increase the crop yield[7-9]. However, with the extension of the implementation time of protective tillage, the disadvantages of protective tillage measures are also gradually emerging. For example, long-term less and no-tillage will lead to the accumulation of nutrients in the surface soil, which is not favorable for the uniform distribution of nutrients in the deep soil, accordingly influencing the crop yield[10-11].

As an important grain producing area in northwest China, the dry loess plateau area is located in arid and semi-arid areas and belongs to the rain-fed agriculture area. With the rise of protective tillage research, no-tillage operation has been carried out on the experimental field in the study area for three years. Some study has indicated that long-term no-tillage condition may lead to the accumulation of nutrients in the surface soil of the farmland, while the deep soil layers will have less soil nutrients, then the soil nutrients are not balanced, accordingly limiting the crop yield[12]. In order to find out the effects of long-term no-tillage operation on soil nutrient content in the study area, we performed different tillage treatments for the soil after long-term no-tillage. We selected the dry loess plateau area as the study area. In line with existing problems in the long-term no-tillage, we analyzed the effects of long-term no-tillage on the contents of available phosphorus and available potassium in e winter wheat 0-30 cm soil layer, to provide a scientific reference for establishing a proper crop rotation system.

2 Overview of the study area and research methods

2.1OverviewofthestudyareaThe experiment area is located in Changwu loess plateau agri-ecological experiment station of the Northwest A&F University of Changwu County of Shaanxi Province (35°14′ N, 107°40′ E). It belongs to arid agricultural area, and has temperate semi-humid monsoon climate. The crop planting is mainly one-crop-a-year wheat and maize. The experiment site is 1 200 m above sea level, with an annual average temperature of 9.1℃, sunshine hours of 2 226 h, and annual average rainfall of 578.5 mm. The soil in the experimental field is loessial soil, the field water holding capacity is 21%-24%, the wilting humidity is 9%-12%, the tillage soil pH is 8.4, and the bulk density is 1.36 g/cm3.

2.2ExperimentaldesignandtillagemethodIn September 2015, we carried out no-tillage, tillage, and rotary tillage treatments for the winter wheat before sowing in the no-tillage experimental field for three consecutive years, repeated three times, as listed in Table 1. The amount of fertilizer applied to each treatment was in accordance with the local farmers’ management model. The winter wheat variety adopted Changhan 58, and the seeding amount was 150 kg/ha, sowed on September 29, 2015, and harvested on June 4, 2016.

Table1Experimentaltreatmentmethods

2.3SamplingschemeanddeterminationmethodsAfter harvesting the wheat, we took three points on the experimental field with soil drill, took the soil depth to 30 cm, and collected sample according to 0-10, 10-20 and 20-30 cm, took about 40-50 g into the aluminum box, and measured the soil water content[13]; separately, took some soil sample (350-450 g) and placed in a resealable bag to measure the available phosphorus and available potassium in the soil. According to theSoilAgrochemicalAnalysis(third edition) edited by Bao Shidan, we determined the soil available phosphorus content by 0.5 mol/L NaHCO3extraction colorimetric method, and determined the soil available potassium content by ammonium acetate extraction-flame photometry[14].

2.4DataprocessingWe used the mean and standard deviation to indicate the soil available phosphorus and available potassium in different tillage methods and different depths. Besides, we performed One-way ANOVA to analyze the effects of different tillage methods on soil available phosphorus and available potassium. Finally, we analyzed the data byLSDmethod. The results indicate that there were significant differences between the two (P<0.05). We processed the data using Excel 2007, and analyzed the data with the aid of software SPSS 20.

3 Results and analysis

3.1SoilavailablephosphoruscontentunderdifferenttillagemethodsAs shown in Table 2, in the 0-30 cm soil layer, the soil available phosphorus content decreased with the increase of soil depth under the three tillage modes. Under no-tillage method, the available phosphorus content in the 10-20 cm soil layer and 20-30 cm soil layer reduced by 16.07% and 32.74%, respectively; the available phosphorus content in the 20-30 cm soil layer was 19.86% lower than that in the 10-20 cm soil layer; there were significant differences (P<0.05); under tillage method, the available phosphorus content in the 10-20 cm soil layer and 20-30 cm soil layer reduced by 2.01% and 7.38%, respectively, compared with that in 0-10 cm soil layer; the available phosphorus content in the 10-20 cm soil layer was 5.48% lower than that in the 10-20 cm soil layer; there was no significant difference between them (P<0.05); under rotary tillage method, the available phosphorus content in the 10-20 cm soil layer and 20-30 cm soil layer reduced by 5.96% and 18.54%, respectively, compared with that in 0-10 cm soil layer; the available phosphorus content in the 20-30 cm soil layer reduced by 13.38% compared with that in the 10-20 cm soil layer; there was no significant difference between 0-20 cm soil layer and 10-20 cm soil layer, while there were significant differences between other soil layers (P<0.05). Under different tillage methods, the available phosphorus content in the 0-10 cm soil layer by tillage method reduced by 11.31% compared with that by no-tillage, and there was no significant difference between other tillage methods (P<0.05). In 10-20 cm soil layer, there was no significant difference between three tillage methods; in 20-30 cm soil layer, the available phosphorus content by tillage method significantly increased by 18.12% compared with that by no-tillage, and there was no significant difference between others (P<0.05).

Table2Averagesoilavailablephosphoruscontentunderdifferenttillagemethods(±standarddeviation) (mg/kg)

Soil layer∥cm No-tillageTillageRotary tillage0-10 16.8±0.954 aA 14.9±0.751 bA 15.1±0.814 abA10-20 14.1±0.814 aB 14.6±0.889 aA14.2±0.643 aA20-30 11.3±1.153 bC 13.8±0.854 aA12.3±1.100 abB

Note: small letters represent the difference in soil available phosphorus content between different tillage methods at 0.05 level; capital letters represent the difference in soil available phosphorus content between different soil layers at 0.05 level. The same as below.

3.2SoilavailablepotassiumcontentunderdifferenttillagemethodsAccording to Table 3, similar to the soil soil available phosphorus, in the 0-30 cm soil layer, the soil available potassium content decreased with the increase of soil depth under the three tillage modes. The available potassium content in the 10-20 cm soil layer and 20-30 cm soil layer reduced by 15.54% and 27.08%, respectively, compared with that in 0-10 cm soil layer; the available potassium content in the 20-30 cm soil layer was 13.67% lower than that in the 10-20 cm soil layer; there were significant differences between them (P<0.05). Under tillage method, the available potassium content in the 10-20 cm soil layer and 20-30 cm soil layer reduced by 2.54% and 6.19%, respectively, compared with that in 0-10 cm soil layer; the available potassium content in the 10-20 cm soil layer was 3.75% lower than that in the 10-20 cm soil layer; there was no significant difference between them (P<0.05). Under rotary tillage method, the available potassium content in the 10-20 cm soil layer and 20-30 cm soil layer reduced by 7.81% and 15.91%, respectively, compared with that in 0-10 cm soil layer; the available potassium content in the 20-30 cm soil layer reduced by 8.79% compared with that in the 10-20 cm soil layer; there were significant differences between only the 0-10 cm soil layer and 20-30 cm soil layer (P<0.05). Under different tillage methods, the available potassium content in the 0-10 cm soil layer by tillage and rotary tillage methods reduced by 6.16% and 4.97% compared with that by no-tillage (P<0.05), and there was no significant difference between three tillage methods in 10-20 cm soil layer; in 20-30 cm soil layer, the available potassium content by tillage method significantly increased by 17.17% and 9.22% compared with that by no-tillage and rotary tillage methods, respectively (P<0.05).

Table3Averagesoilpotassiumcontentunderdifferenttillagemethods(±standarddeviation) (mg/kg)

Soil layer∥cm No-tillageTillageRotary tillage0-10 142.9±2.511 aA134.1±3.934 bA135.8±2.589 bA10-20 120.7±6.067 aB130.7±4.518 aA125.2±8.994 aAB20-30 104.2±6.619 bC125.8±5.197 aA114.2±3.769 bB

4 Discussions

The change of tillage mode is mainly the change of tillage depth. And the tillage depth is closely related to soil bulk density, soil porosity, plant roots and soil nutrient content[15-16]. According to this study, in 0-30 cm soil layer, the soil available phosphorus and available potassium decreased with the increase of the soil depth under no-tillage, tillage, and rotary tillage methods. This is consistent with findings of Gao Xiaodong in the Loess Plateau, that is, the nutrient content decreases with the deepening of the soil layer[17]. This is because the application of surface fertilizer and litter increase the soil surface nutrient content, while the deep soil nutrient mainly depends on the secretion of roots. No-tillage mainly affects the available phosphorus and available potassium in the soil surface, while tillage mainly affects the available phosphorus and available potassium in the deep soil.

In this study, the soil available phosphorus and available potassium under different tillage methods were in no-tillage>rotary tillage>tillage, there was no significant in the soil available phosphorus and available potassium between tillage and rotary tillage, while there were significant differences between no-tillage and other two tillage methods (P<0.05). Compared with rotary tillage and tillage, no-tillage treatment can reduce the disturbance to the soil surface and increase the soil surface nutrient content, which is consistent with the findings of Hou Xianqingetal.[18]. By comparison, the soil available phosphorus and available potassium in 10-20 cm soil layer and 20-30 cm soil layer were tillage>rotary tillage>no-tillage, and there were significant differences between no-tillage and tillage treatment (P<0.05). According to the analysis, the tillage treatment can break the bottom layer of the plow, so it is favorable for the absorption of nutrients in the lower soil by the crop and can improve the availability of available phosphorus in the deep soil, reducing the available phosphorus and available potassium in the surface soil, but increasing the nutrient content of the deep soil, which is consistent with the results of Zhang Wenchao[19].

5 Conclusions

According to this experiment, the tillage and rotary tillage in long-term no-tillage loess plateau can reduce the accumulation of the soil available phosphorus and available potassium content in the soil surface. In the 0-10 cm soil layer, the soil available phosphorus content by tillage method significantly reduced by 11.31% compared with no-tillage, while the available potassium content under tillage and rotary tillage significantly reduced by 6.16% and 4.97%, respectively. In addition, it can increase the distribution of available phosphorus and available potassium in deep soil. In the 20-30 cm soil layer, the available phosphorus and available potassium content by the tillage method increased significantly by 18.12% and 17.17%, respectively, compared with that by no-tillage method. Therefore, in long-term no-tillage loess plateau, it is necessary to conduct proper tillage and rotary tillage, to realize balance of nutrients in different soil layers, so as to improve the soil productivity.