| The Loess Region（LR）,located in the northwest China.It’s an important grain-producing region in China,playing a vital role in ensuring regional food supply and food security.However,agricultural practices in LR is limited by soil nutrient deficiencies and water shortages,which directly lead to low soil fertility and crop yields.In particularly,the newly-construction cultivated land and degraded cultivated land cannot be rapidly upgraded in the short term to meet the needs of modern agricultural development.In addition,the relationship between the yields of two typical crops（wheat and maize）and the maintenance of soil fertility and efficient use of soil and water resources under traditional dryland agricultural cropping systems in LR still needs to be deepened.In this study,wheat and maize,the main food crops in LR,were used as the research objects.The effects of exogenous organic materials addition on soil organic matter and crop yield in newly-construction cultivated land and degraded arable land were investigated through field trials and pot experiments.To explore the ways of rapid soil fertility enhancement and the underlying mechanisms in newly-construction cultivated land and degraded cultivated land.At the same time,relying on the National Field Scientific Observation and Research Station for Agricultural Ecosystems in Changwu,Shaanxi Province,a continuous five-year field trial（from September,2015 to June,2020）were conducted at the long-term field experiments.To evaluate the combined effects of five fertilization treatments,six patterns of plastic-film mulching under the continuous winter wheat crop system and eight conservation tillage practices under continuous spring maize crop system on soil hydraulics,physics,chemistry,crop growth characteristics,water resources utilization,crop yield and biomass.The research is aimed to provide scientific evidence for the improvement of soil fertility and efficient utilization of soil and water resources in newly-construction cultivated land,degraded cultivated land and traditional cropland in LR.The main results and conclusions obtained from this study are as follows:（1）Proposed a fertilization model for the rapid construction of a high-quality tillage layer in newly-construction cultivated land using engineering measures via three consecutive years of field trials from 2016 to 2018.In details,based on eliminating obstacles to the construction of a high-quality tillage layer,the content of inert soil organic matter was rapidly increased by adding woody peat as an exogenous organic material at one time.The mineralization and decomposition rate of woody peat was regulated by bio-initiated regulators,and straw returning and chemical fertilizers application were applied to supplement the soil available nutrient content in newly-construction cultivated land.The results showed that the soil organic matter content of 0-15 cm in the harvest period in 2016,2017 and 2018 increased by 16.7%,31.8%and 93.9%under this fertilization model,respectively,as compared with the control treatment.The stability of soil water-stable aggregates was enhanced,the content of soil readily oxidized carbon increased,and the maize yield increased by an average of 8.2%in the three years from 2016 to 2018.（2）Compared the rapid fertilization effect of woody peat in degraded soils with four different textures（degraded black soil,loessial soil,lou soil,and degraded red soil）through pot experiments.The results showed that the addition of woody peat increased the soil organic matter content of all four degraded soils compared to the control.In the 0-20 cm soil layer at harvest,soil organic matter content of degraded black soil,loessial soil,lou soil and degraded red soil increased by 40.4%,40.0%,101.3%and 94.6%,respectively.There was a significant positive correlation between soil organic matter content and wheat yield after the addition of woody peat.Soil organic matter in the 0-20 cm soil layer was reduced by 5.1 g kg-1（degraded black soil）,9.9 g kg-1（loessial soil）,7.6 g kg-1（lou soil）and 6.2 g kg-1（degraded red soil）at harvest in each treatment compared to sowing stage of wheat.Except for the coarse-textured loessial soil,among the three medium-textured soils（degraded black soil,lou soil,and degraded red soil）,the higher soil clay content,the smaller the change in soil organic matter,and the change in soil organic matter first decreased and then increased as the clay content increased.（3）Through the field experiments,the effects of different fertilization treatments and plastic-film mulching patterns on soil physicochemical properties,winter wheat yield and water resource utilization in the continuous cropping system of winter wheat on traditional cropland from 2016 to 2020 were comprehensively described.The results showed that:（1）under different fertilization treatments,the multi-combined development index values of the NPK treatment,NP with biochar treatment,NP with organic fertilizer instead of straw returning treatment were 16.8%,12.9%and 0.4%,respectively.Compared to the NP treatment,the NPK treatment significantly increased winter wheat yield by 12.8%-29.2%（P<0.05）between 2016-2020,and 5-year average water use efficiency and rainfall utilization efficiency increased by 49.2%and 19.6%respectively.The average grain yield,water use efficiency and rainfall utilization efficiency of winter wheat increased by 9.9%,59.6%and10.1%respectively in five years under the NP with biochar treatment.（2）Under different plastic-film mulching patterns,the six plastic-film mulching treatments increased winter wheat yields by an average of 32.2%in dry years（2016,2018）and normal years（2017,2020）compared to the traditional tillage without mulching treatment,and increasing by an average of 60.4%in wet year（2019）.The multi-combined development index values under the 50%coverage rate of plastic-film mulching in fallow period treatment,100%coverage rate of plastic-film mulching in fallow period treatment,50%coverage rate of plastic-film mulching in growth period treatment,100%coverage rate of plastic-film mulching in growth period treatment,50%coverage rate of plastic-film mulching in growth year treatment,and100%coverage rate of plastic-film mulching in growth year treatment based on traditional tillage without mulching were 5.4%,-0.1%,9.3%,7.6%,4.3%and 7.2%,respectively,the water use efficiency increased by 53.5%,23.0%,7.3%,40.0%,38.6%and 23.7%respectively compared to the traditional tillage without mulching treatment.The low mulching rate and short mulching time of the 50%coverage rate of plastic-film mulching in growth period treatment had the best comprehensive impact on soil physical and chemical properties,crop yield and water resources utilization.（4）Through the field located experiments,the mechanism of efficient utilization of water and soil resources under the conservation tillage measures of spring maize in traditional cultivated land during 2017-2019 was systematically analyzed.The results showed that:（1）compared with the traditional tillage without mulching treatment,in the 0-10cm soil layer,the plastic-film mulching treatment significantly increased the stability of soil water-stable aggregates,increased the geometric mean diameter and mean weight diameter of water-stable aggregates by 57.4%and 63.9%,respectively,but the straw mulching treatment decreased by 14.7%and 4.4%,respectively.Plastic-film mulching treatment increased soil bulk density and soil air permeability,and affected maize root traits through aggregate stability.The average maize yield,water use efficiency and rainfall utilization efficiency increased by 18.7%,13.0%and 18.9%,respectively,from 2017 to 2019 under the plastic-film mulching treatment,but there was uncertain effect of the straw mulching treatment on spring maize yield,and reduced water use efficiency and rainfall utilization efficiency in both 2017 and 2019.（2）compared with traditional tillage,no-tillage combined with plastic-film mulching increased soil bulk density and stability of soil water-stable aggregates,improved soil water content and soil water storage,and increased spring maize yield by 12.7%-36.5%from 2017 to 2019.No-tillage combined with straw and plastic-film mulching changed the soil bulk density and water and air transport characteristics in the 0-40cm soil profile,improved the stability of soil water-stable aggregates,increased soil water storage in the 0-300 cm soil layer,improved water use efficiency and rainfall utilization efficiency in 2018-2019,which had a positive effect on spring maize yield.Depending on the type of cultivated land,soil fertility enhancement and efficient utilization of soil and water resources in LR need to be applied to different types of cultivated land（newly-construction cultivated land,degraded cultivated land and traditional cropland）.The use of one-time input of stable exogenous organic material（woody peat）,combined with straw returning and fertilizer application,is a rapid way to improve the soil fertility of newly-construction cultivated land and degraded soils in LR.For traditional cropland in LR,winter wheat cultivation should be fertilized with NPK fertilizers or NP fertilizers with biochar,combined with plastic-film mulching at the coverage rate of 50%during the growth period,which can improve the soil fertility,increase the grain yield of winter wheat and the efficiency of soil and water resources utilization.Spring maize cultivation should use no-tillage combined with plastic-film mulching or no-tillage combined with straw and plastic-film mulching conservation tillage measures,which are conducive to maintaining soil fertility,improving spring maize production and water use efficiency.The corresponding measures for different types of cultivated land are not only important for the improvement of soil fertility and the efficient utilization of water and soil resources in LR,but also provide a reference for the high-quality development of dryland agriculture in the region. |
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