| The loess plateau,as the main apple producing area in China,the improvement of apple yield and quality and the sustainable development of orchard must be inseparable from the orchard soil environment suitable for fruit tree growth as the basic guarantee.In recent years,orchard mulching has become a soil management pattern popularized in orchard production,including raw grass cover,straw cover and so on,which is a key measure to improve organic matter and biodiversity in orchard soil.Soil dissolved organic matter(DOM)plays a very important role in soil carbon and nitrogen and can reflect soil quality status to a certain extent.However,there are few reports on the influence of soil dissolved organic matter in different soil management pattern.In this study,the effects of different soil management pattern in orchards in arid and semiarid areas on soil DOM content,composition and spectral characteristics were analyzed under different exogenous organic matter input conditions using a combination of fluorescence excitation–emission spectroscopy and parallel factor analysis(EEM-PARAFAC),in order to provide data and theoretical support for the improvement of orchard soil quality and the study of production practice.The main results of this study are as follows:(1)The soil dissolved organic matter of different mulching pattern has obvious difference in content,composition and source.Under Different Orchard Mulch Measures,the total soil organic carbon(SOC)and dissolved organic carbon(DOC)content were ranked as intercropping straw mulch > intercropping perennial ryegrass mulch > clean tillage,and decreased with increasing soil depth.In addition,the vertical distribution of DOC with different soil depth was caused by organic matter input but not leaching.The intercropping perennial ryegrass mulch was more favourable than others for the dissolution of soil organic carbon.Three humic-like components(C1,C2,C3)and two protein-like components(C4,C5)were identified by EEM-PARAFAC.Fluorescence spectra showed that humic-like compounds were the dominant fractions in soil DOM in the intercropping mulch straw.Fluorescence Index indicated that the proportion of DOM from the terrestrial source ranked as clean tillage > intercropping perennial ryegrass mulch > intercropping straw mulch and gradually decreased with soil depth.Intercropping mulch plays an important role in improving the content and composition of soil DOM through the input of different forms of organic matter.(2)The content,composition and fluorescence characteristics of dissolved organic matter in soil showed the dynamic evolution characteristics of slow,rapid and tend to balance with different herbage ages.White clover with different herbage ages,the DOC content ranked as follows: 12-yr WC > 8-yr WC > 4-yr WC > CT.The soil dissolved organic nitrogen(DON)content increased slowly after 4 years of raw grass,while it increased rapidly in years 4-8 and remained largely unchanged in years 8-12.Three humic-like components and two protein-like components were identified by EEM-PARAFAC.The total fluorescence intensity change was similar to the change in DON contents.It is worth noting that the fluorescence intensity of component 5 was the highest in the 8-yr WC.The SUVA254 values were ranked as follows: 12-yr WC > 8-yr WC > 4-yr WC > CT.The fluorescence index tended to increase with soil depth.The humification index(HIX)increased with herbage age,and the largest value was obtained in the 0-20 cm soil layer.Intercropping orchard with white clover plays a key role in improving soil DOM content and composition through the different degrees of root function with herbage age.(3)The release of organic matter in the process of decomposition of raw grass is obviously superior to that of grasses.The average rate of decomposition of different grass species was white clover(WC)> crown vetch(CV)> orchardgrass(OG).EEM-PARAFAC identified the DOM of each grass species as one humic acid-like component(C1)and two protein-like components(C2,C3).The fluorescence intensity of the protein-like components was much higher than that of the humic acid-like components,and the C2 component was dominant in the three components.The values of total fluorescence intensity were higher than that of white clover and crown vetch.The microbial source is the main source in the process of crown vetch treatment in the process of decay,while white clover and orchardgrass are mixed sources,that is,terrestrial plant h?mus and microbial source.The h?mification index(HIX)value of each grass species were ranked as follows: CV > OG > WC.The SUVA254 values were ranked OG > CV > WC,and increases with the number of days of decay.There was no obvious change trend in the SR value of each grass.Compared with Gramineae,legumes have great influence on DOM content,composition and spectral characteristics,and release organic matter more fully. |
PDF Full Text Request