| Water is a major factor limiting the recovery of vegetation and agricultural development in the Loess Plateau region,and the addition of soil amendments is one of the most important ways to improve the soil water use efficiency and increase food production in this region.Soil amendments can improve the water storage capacity of soils,but they also tend to affect or reduce the ability of crops to absorb water from the soil under drought conditions.Therefore,the effect of soil amendments on crop growth in rainfed areas is a complex issue that is influenced by a combination of soil type,amendment dosing and meteorological conditions.The clay mineral Attapulgite（ATP）is widely distributed and its special colloidal properties and crystal structure make it excellent for improving the physical and chemical properties of soils,and is used as a soil conditioner as it contains constant and trace elements required by plants.In this paper,ATP was used as the research object,and four typical soils（lou soil,dark loessial soil,cultivated loess soil,and sandy soil）of Loess Plateau with different textures were selected and five ATP addition levels（0%,1%,2%,3%and 4%）were set.By conducting indoor simulation tests,maize pot trials and maize field trials,systematically analyzed the effects of ATP on the hydraulic characteristics,soil structure and soil water effectiveness of typical soils of Loess Plateau.A water characteristic curve model containing ATP content was preliminarily constructed,and the reliability of the soil water characteristic curve containing ATP was verified by simulating the one-dimensional water movement process of the soil with the help of the SWMS＿2D model.The DSSAT crop model was used to simulate maize yields at three sites（Yangling,Changwu,and Yan’an）on the Loess Plateau,and to explore the effects of ATP application on maize yields and reasonable application amount in typical areas of the Loess Plateau,and mainly achieved the following research results:（1）The application of ATP could improve soil water holding capacity,reduce soil hydraulic conductivity and enhance soil stability by measuring the soil water characteristics curve and the stability of soil aggregates.The field capacity,wilting point water content and available water content of the four soil types were positively correlated with the amount of ATP added.The average available water content of the lou soil,dark loessial soil,cultivated loess soil,and sandy soil increased by 4.01%,3.40%,13.66%,and 14.94%respectively compared with the control treatment.The van Genuchten model for ATP-containing soils was developed by fitting a modified van Genuchten model to the water characteristic curve,and the parameters of the model were calibrated by genetic algorithm.ATP addition reduced soil unsaturated conductivity,water capacity and diffusivity.The application of ATP improved the mechanical and water stability of the different soil types when ATP was applied at≤3%,and the addition of ATP reduced soil stability when ATP was applied above 3%.（2）The soil evaporation experiment was carried out through a micro-evaporator to explore the effect of ATP addition on the evaporation process and the characteristics of the cracks on the evaporation surface.The results showed that evaporation decreased with increasing ATP addition in all four soil types when ATP was added at<3%,while the evaporation loss ratio increased in lou soil and dark loessial soil when ATP is added above 3%.The crack area,crack aperture,and fractal dimension of lou soil and dark loessial soil with high clay content increased significantly with the addition of ATP,which increased the effective evaporation area of the soil and thus increased soil evaporation.（3）Soil air and water transport characteristics under ATP addition and the interrelationship with pore structure were investigated by measuring soil saturated hydraulic conductivity,relative gas diffusivity and air permeability.The results showed that saturated hydraulic conductivity,relative gas diffusivity and air conductivity all decreased with increasing ATP amount,with differences between treatments depending on soil pore characteristics（air filled porosity,pore tortuosity,pore connectivity,and pore size distribution）.ATP addition resulted in an increase in micropores pores and a decrease in macropores,with a maximum increase of 52.8%in micropores and a maximum decrease of 35.2%in macropores.ATP addition reduced soil pore connectivity and increased soil pore tortuosity.A saturated hydraulic conductivity prediction model was developed using the relationship between air filled porosity and gas transport parameters via a soil conversion function,and error analysis showed that relative gas diffusivity can be better calculated for saturated hydraulic conductivity than air conductivity.（4）The growth physiological indexes and photosynthetic physiological parameters of maize were measured by pot experiment,and the effect of ATP on the physiological process of maize and soil water availability under different water conditions was explored based on the response characteristics of ATP to soil hydraulic properties.The results showed that（1）under the three kinds of water regulation,the application of ATP reduced maize plant height and biomass in lou soils under normal moisture treatment,and under drought stress and drought-rehydration treatments,the application of ATP favoured maize growth in lou soils,dark loessial soil and cultivated loess soil.（2）In the three types of soils,the promotion effect of ATP on maize growth was shown to be cultivated loess soil>dark loessial soil>lou soils.For lou soil,ATP promoted maize growth under drought-rehydration and water stress treatments,and the addition of ATP under normal water regulation was detrimental to maize growth.For dark loessial soil and cultivated loess soil,ATP showed a facilitative effect on maize growth under all three moisture regimes.（3）The changes in photosynthetic parameters（leaf net photosynthesis,transpiration,stomatal limitation,stomatal conductance,intercellular CO2 concentration and water use efficiency）of maize leaves in different soil types under ATP treated showed a threshold response based on relative soil water content,with a certain deviation from the threshold leading to a reduction in photosynthetic physiological indicators.（4）The differences in water critical thresholds and water grading for the different photosynthetic parameters of the treatments were analysed.Soil water effectiveness was higher under the 2%ATP treatment than the 4%ATP treatment and the control treatment,and soil water effectiveness was higher in dark loessial soil and cultivated loess soil than in lou soil after the application of ATP.（5）Through field maize experiments,using the influence characteristics of ATP on soil water characteristic curve parameters,the SWMS＿2D model was used to simulate the soil water movement process in the growth period of maize under different ATP additions by improving the van Genuchten model parameters.The error analysis showed that the improved van Genuchten model could better simulate soil water movement when compared with the measured soil profile water content at different fertility stages of maize.In order to explore the reasonable ATP incorporation rate for improving maize yield,the DSSAT model was used to evaluate the differences in maize yield in Yangling（lou soil）,Changwu（dark loessial soil）and Yan’an（cultivated loess soil）areas over the years（2011-2020）after different ATP additions.The results showed that maize yields in Yangling generally decreased with increasing ATP application between from 2011 to 2020,but in years with relatively low rainfall maize yields were positively correlated with ATP application.Maize yield in the Yan’an area was positively correlated with ATP application.Maize yields in the Changwu area varied considerably between years,with inflection points at 4%,6%and 8%ATP application.The reason for this may be related to the clay content of the soil and the rainfall during the crop reproductive period,which showed that the addition of ATP in areas with low clay content and low rainfall was beneficial to maize growth and vice versa,while the amount of ATP should be increased in areas with low clay content or rainfall if it was beneficial to crop growth and reduced in the opposite direction.The effect of soil amendments on crop growth is a very complex issue,involving a variety of influences such as soil type and climatic conditions.In this paper,indoor,pot and field trials on a variety of typical soils were carried out,and some systematic conclusions were drawn.However,due to time and conditions,the pot trials on the three soil types were conducted under the climatic conditions of Yangling,and the field trials were conducted in the Yangling area,the reliability of simulation studies in other areas need further validation.Therefore,the effects of ATP addition on the growth of a variety of crops under a variety of soil types and climatic conditions should also be carried out in the future to obtain more systematic conclusions. |
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