The Changing Characteristics of Profile Distribution of Organic Nitrogen

Huan LIU Qian GAO Shiyuan LIU Jie LI Yu WANG Jicheng HAN Yong GUO

Components in Apple-pear Orchard Soil

Abstract In order to evaluate the effects of soil depth on the contents of soil organic nitrogen， organic nitrogen forms in apple-pear orchard soil profile were quantified using the method proposed by Bremner in 1965. The results indicated that in addition to the amino sugar-N， all the soil organic N components within the same soil layer in wasteland were more than those in apple-pear orchard soil; with the layer depth increasing， the contents of different organic nitrogen forms in apple-pear orchard soil and wasteland were decreased; and the proportion of each organic N component within total hydrolysable N was different， and the percentages of ammonia N and amino acid-N components within total hydrolysable N were higher， especially the percentage of ammonia N components within total hydrolysable N was the highest.

Key words Organic nitrogen components; Profile; Apple-pear orchard soil; Distribution characteristics

Received： May 23， 2021  Accepted： July 20， 2021

Huan LIU （1988-）， female， P. R. China， environmental protection engineer， devoted to researchabout fruit tree cultivation and breeding.

*Corresponding author.

Soil is the largest nitrogen reservoir in the orchard ecosystem， and the organic nitrogen is the main form of soil nitrogen and the source of mineral nitrogen. More than 90% of nitrogen in most surface soils is in the form of organic nitrogen. Its content and distribution are affected to varying degrees by factors such as the soil rhizosphere environment， soil layers， types， cultivation conditions and fertilization factor[1-2]. The chemical form and its existing conditions of soil organic nitrogen is one of the important factors affecting the soil nitrogen availability[3]， and its status in soil fertility， nitrogen cycle and environmental protection cannot be ignored. Therefore， great attention has been paid by researchers for a long time[4-7]. Yanbian is the main production area of apple pears， but there is still a lack of comprehensive research on the distribution of organic nitrogen in different soil layers of apple-pear orchards in Yanbian area. In this study， the soil of apple-pear orchard in Yanbian area was selected as the research object to study the content and distribution of organic nitrogen in different soil layers of the soil， and the purpose was to make a positive contribution to the reasonable fertilization of the apple-pear orchard soil in Yanbian area， the study of soil nitrogen cycle and the construction of ecological environment.

Materials and Methods

Test soil

The apple-pear orchard soil of Yanbian University Agricultural College was chosen as the test soil. The sample was collected in 2011. Healthy and well-growing apple-pear trees were randomly selected to arrange the points， a total of four profile points. The uncultivated wasteland adjacent to the apple pear orchard was set as the control profile point， and a total of 5 profile points and 20 samples of soil were arranged. To avoid the fertilization place， the profile point was set one meter away from the trunk. According to the color of the soil， texture， structure， tightness， dry humidity， root distribution and other characteristics， we separated the occurrence levels of soil， followed by the surface layer， sub-surface layer， deposition layer and parent material.

Analysis method

The determination of soil organic nitrogen components adopted Bremner acid hydrolysis method[8]， and the determination of total nitrogen adopted the Kjeldahl method.

Data processing

Data processing used SPSS11.5 analysis software and Excel to statistically analyze the measurement results.

Results and Analysis

Distribution of acid-hydrolysis organic N in soil profile

Using the Bremner acid hydrolysis method[8]， soil organic nitrogen was divided into two parts： acid-hydrolysis organic N and non-acid-hydrolysis organic N. Fig. 1 shows that with the layer depth increasing， the content of acid-hydrolysis organic N forms in apple-pear orchard soil and wasteland were decreased. Among them， the content of acid-hydrolysis organic N showed a significant decrease from layer A1 to layer B of apple-pear orchard soil. However， the decrease from layer B to layer C was not significant. Wasteland is shown in layers A1-C. The content of acid-hydrolysis organic N decreased significantly， and the differences were up to 5% significant level. The acid-hydrolysis organic N within the same soil layer in wasteland was more than that in apple-pear orchard soil.

From the above results， whether for orchard soil or wasteland， the content of total acid-hydrolysis organic N showed a downward trend with the increase of soil depth， which is similar to Dang Yaais research results[9]. The soil acid-hydrolysis organic N components within the same soil layer in wasteland were more than those in apple-pear orchard soil. Many studies at home and abroad have shown that plant roots can absorb organic nitrogen in the soil[10-15]. Therefore， it might be related to the fact that the root system of apple pear trees is more developed than that of wasteland herbaceous plants， and the roots capacity to absorb nitrogen is superior to the grass roots.

Distribution of non-acid-hydrolysis organic N in soil profile

Fig. 1 shows， the same as the acid-hydrolysis organic N， with the layers depth increasing， the content of non-acid-hydrolysis organic N forms in apple-pear orchard soil and wasteland were decreased， and the differences were up to 5% significant level. In addition to the A2 layer， the same soil layer， the non-acid-hydrolysis organic N components in apple-pear orchard soil were more than those in wasteland. Statistical analysis showed that in the four soil layers， the contents of non-acid-hydrolysis organic N in apple-pear and wasteland were more than those of acid-hydrolysis organic N.

Distribution of ammonia N in soil profile

As shown in Fig.  with the layer depth increasing， the contents of ammonia N in apple-pear orchard soil and wasteland showed a significantly decreasing trend， which is consistent with the research results of Li Jumei[16]. Among them， the differences in ammonia N content between the A1 layer and the A B and C layers of the apple pear orchard soil reached a significant level of 5%， and from the B to the C layer， ammonia N content did not decrease significantly; and the wasteland showed the four soil layers of A1-C having significant differences in ammonia N content at the level of 5%.

The ammonia nitrogen contents of all soil layers in wasteland were more than those in apple-pear orchard soil. Because the amino acids can be absorbed and utilized by plant roots after being decomposed， it might be related to the facts that the roots are more developed than grass roots.

Distribution of amino sugar-N in soil profile

As shown in Fig.  the content of amino sugar-N was very low. From layer A1 to layer B of the apple pear orchard soil， amino sugar-N content showed a downward trend; and from the B to the C layer， the content of amino sugar-N was on the rise. There were no obvious changes in the content of amino sugar-N in different soil layers of wasteland. The amino sugar-N contents of all soil layers in apple-pear orchard soil were more than those in wasteland.

The above results showed that the content of amino sugar-N in wasteland was relatively stable. It might be because amino sugar-N mainly comes from the biosynthesis of soil microorganisms， and might also be related to the larger amount of inter-root microorganisms in orchard soil than in wasteland. Chen et al.[17] showed that inter-root microorganisms were the most active components associated with plant roots and soil.

Distribution of amino acid-N in soil profile

Fig. 2 shows， from the A1 to the C layer， with the layer depth increasing， the contents of amino acid-N in apple-pear orchard soil and wasteland were decreased significantly. From layer A1 to layer B of apple pear orchard soil， amino acid-N content decreased significantly， and from layer B to layer C， its content decline was not significant; and the change trend of amino acid-N content in wasteland was the same as that of apple-pear garden soil.

The amino acid-N contents of all soil layers in wasteland were more than those in apple-pear orchard soil. It might be related to the ability of the root system to absorb amino acids from the soil. The root system of apple pear trees is more developed than that of wild grass， so it absorbs more amino acid-N.

Distribution of unknown-N in soil profile

As shown in Fig.  from the A1 to the C layers， with the layer depth increasing， the contents of unknown-N in apple-pear orchard soil and wasteland were significantly decreased. There were significant differences in the content between the A1 and A B and C layers. And the unknown-N contents of all soil layers in wasteland were more than those in apple-pear orchard soil.

The ratio of organic nitrogen components to total nitrogen in soil at different profile layers

Fig. 3 shows that the profile distribution of the total nitrogen ratio of the organic nitrogen components of apple-pear garden soil and wasteland was not consistent. In the soil of the apple-pear orchard， the ratio of ammonia N and amino sugar nitrogen to total nitrogen had no obvious change with the increase of soil depth; the ratio of amino acid N to total nitrogen increased first and then decreased with the increase of soil depth; and the ratio of unknown nitrogen to total nitrogen gradually decreased with the increase of soil depth. However， in the soil of the wasteland， the ratio of amino acid nitrogen to total nitrogen decreased with the increase of soil depth trend.

It can also be seen in Fig. 3， in the four soil layers of apple-pear garden， the order of the content of each component of organic nitrogen in apple pear orchard soil was ammonia nitrogen>amino acid nitrogen> unknown nitrogen>amino sugar nitrogen. For layers A1 and A2 in the wasteland， the order of the content of each component of organic nitrogen was the same as that of apple pear orchard soil， while the order of the content of each component of organic nitrogen in layers B and C was ammonia nitrogen> unknown nitrogen>amino acid N>amino sugar nitrogen.

Conclusions

In general， different soil layers had different organic nitrogen components. The specific manifestation was that with the gradual increase of soil depth， acid-hydrolysis organic N content， non-acid-hydrolysis organic N content and organic nitrogen components of apple pear orchard soil and wasteland showed a downward trend.

In general， in the same soil layer， the contents of amino sugar nitrogen and non-acid hydrolysis nitrogen of wasteland were lower than those of apple pear orchard soil， while the content of acid hydrolysis total nitrogen， acid hydrolysis ammonia nitrogen content， amino acid nitrogen content and the unknown nitrogen content were higher than those of apple pear orchard soil.

Proportions of various fractions of organic N to total N in apple-pear orchard soil and wasteland were different， and the common feature was that both acid-hydrolysis ammonia nitrogen and amino acid-nitrogen occupied a higher proportion of organic nitrogen components， especially acid-hydrolysis ammonia nitrogen in the soil of organic nitrogen components accounted for the highest proportion. Acid-hydrolysis ammonia nitrogen and amino acid nitrogen were the most important organic nitrogen forms in Yanbian soil.

References

[1] XIE QF， LIU JR， SHI QH， et al. Effect of different fertilization patterns on rice yield and nitrogen uptake and transformation in soil[J]. Plant Nutrion and Fertilizer Science， 2004， 10（5）： 462-467.

[2] ZHANG JQ， ZHU P， ZHANG FD. Effect of organic manure and chemical fertilizer combined application on the form and distribution of organic nitrogen of black soil[J]. Plant Nutrion and Fertilizer Science， 2004， 10（3）： 245-249.

[3] XIAO WW， FAN XH， YANG LZ， et al. Response of soil organic nitrogen forms and organic carbon to Long-term fertilization in dry highland of Loess Plateau[J]. Journal of Agro-Environment Science， 2007， 26（2）： 672- 675.

[4] MULVANEY RL， KHAN SA， HOEFT RG， et al. A soil organic nitrogen fraction that reduces the need for nitrogen fertilization[J]. Soil Science Society of America Journal， 2001（65）： 1164-1172.

[5] HU XT， LIU XJ， ZHANG FS. Effects of longterm fertilization on soil organic nitrogen fractions[J]. Scientia Agricultura Sinica， 2004， 37（1）： 87-91.

[6] LI LX， HAO MD， PENG LF. Research on variety of soil organic nitrogen components in artificial herbage land on loess plateau[J]. Research of Soil and Water Conservation Mar.， 2003， 10（1）： 55-57， 84.

[7] LI SX， LI SX， SHAO MA， et al. Effects of long-term application of fertilizers on soil organic nitrogen components and microbial biomass nitrogen in semiarid farmland ecological system[J]. Scientia Agricultura Sinica， 2004， 37（6）： 859-864.

[8] LU RK. Soil agricultural chemical analysis method[M]. Beijing： China Agricultural Science and Technology Press， 2000.

[9] DANG YA， WANG GD， LI SQ. The changing characteristics of profile distribution of soil organic nitrogen component of the typical soil types on the loess plateau[J]. Scientia Agricultura Sinica， 201 44（24）： 5021-5030.

[10] WLH， TAO QN. Research progress on plant organic nutrition[M]. Beijing： China Agricultural University Press， 2000： 58-71.

[11] NASHOML T， PERSSON J. Plant acquisition of organic N in boreal forests[J]. Physiology Plantarum， 2001（111）： 419-426.

[12] JONES DL， HEALEY JR， WILLETT VB， et al. Dissolved organic nitrogen up take by plants Anmi-portant N uptake pathway[J]. Soil Biology and Biochemistry， 2005（37）： 413-423.

[13] MO LY， WU LH， TAO QN. Advances in study of plant organic nitrogen nutrition[J]. Acta Ecologica Sinica， 200 22（1）： 118-124.

[14] NASHOML T， KIELLAND K， GANETEG U. Uptake of organic nitrogen by plants[J]. New Phytologist， 2009（182）： 31-48.

[15] WANG WY， LIU JY. Research advances in organic nitrogen acquisition by plants[J]. Chinese Journal of Applied Ecology， 2009， 20（5）： 1223-1228.

[16] LI JM， LI SX. Relation of mineralizable N to organic N components[J]. Plant Nutrition and Fert ilizer Science， 2003， 9（2）： 158-164.

[17] CHEN W， JIANG ZW， HU YL. Study on biological character of rhizosphere microorganism in apple orchard[J]. Journal of Soil and Water Conservation， 2008， 22（3）： 168-171.