田间原位试验分析长期机械作业下稻麦轮作地块土壤入渗性能

Soil infiltration of rice-wheat rotation field under long-term mechanical treatment based on field in situ experiments

田间原位不同深度入渗试验是表达土壤分层状态、展示土层物理分异以及定量土壤剖面水功能变化的关键。为了探究不同深度水稻土的入渗能力及保水作用,该研究以华东稻麦轮作区小农户长期机械化耕整模式下代表地块的土层分异为目标,设计田间原位不同深度入渗试验。在试验地块内开挖7个不同深度的入渗坑并在坑底进行入渗试验,然后渗透48 h分层测取土壤含水率,研究不同坑底深度(坑深)土壤的入渗能力和入渗后各土层含水率的变化。结果表明,不同深度入渗试验准确表达了不同坑深土壤的水分入渗及土层持水分异,同时也能清晰地鉴别出犁底层所在位置和厚度,犁底层始于15 cm深,且耕作层与犁底层分异明显,耕作层平均紧实度为1005.79 kPa,犁底层平均紧实度为1910.73 kPa;土壤剖面分析表明,耕作层土壤形态疏松,根系分布稠密,犁底层土壤容重大,孔隙度小,透水性差,心土层土壤铁锰斑点较多,结构性差;土壤入渗参数随坑深的增加而减少,其中0~15 cm坑深范围内平均的平均入渗速率和累计入渗量分别为>20~30 cm的17.04倍和18.06倍;通过对比初始含水率和渗透48 h后含水率,得到坑深在15 cm范围内的水分入渗深度均为距表土20cm,而大于15cm坑深的水分入渗深度均为坑深以下10cm;利用Horton、Kostiakov和Philip3个模型拟合不同坑深入渗,结果表明,Kostiakov模型的拟合参数与实际相符且R^(2)最高(0.98~0.99),均方根误差最小(0.01~0.77mm/min)。入渗参数与土壤容重、含水率、总孔隙度和田间持水量有极显著的相关性(P<0.01),与土壤紧实度相关性不显著(P>0.05)。该研究通过原位不同深度入渗试验,说明华东稻麦轮作区小农户生产模式下长期机械化耕作导致水稻土明显的分层和土壤水功能垂直分异,进而导致耕作层与耕作层以下土层表现出显著的入渗能力差异。研究可为稻麦轮作地区的机械耕作、灌溉等提供借鉴。

Field in situ infiltration experiments at different depths can be used to express the state of soil stratification,and the physical differentiation of soil layers,in order to quantify the changes in the water of the soil profile.This study aims to obtain the infiltration capacity and water retention of paddy soils.The field in situ soil infiltration experiments were also carried out at different depths to identify the soil stratification in the representative plot under long-term mechanized tillage of smallholder farmers in the rice-wheat rotation region of eastern China.Seven infiltration pits of different depths were excavated in the experimental plots.After that,the infiltration experiments were conducted at the bottom of the pits.Soil water content was then measured in the layers for 48 hours of infiltration.A systematic investigation was made to explore the soil infiltration capacity at the bottom of the pits and the soil water content of each layer.The results showed that an accurate description was achieved in the water infiltration and water holding capacity of the soil at different pits after the infiltration experiments at different depths.The location and thickness of the plow pan were also clearly identified during this time.The plow pan was started at a depth of about 15 cm,indicating the outstanding difference between the cultivated layer and the plow pan.The average soil penetration resistances of the cultivated layer and the plow pan were 1005.79 kPa,and 1910.73 kPa,respectively.The soil profile showed that the soil in the cultivated layer shared a loose morphology and dense root distribution,whereas,the soil in the plow pan presented a high bulk density,low porosity,and poor permeability,while the soil in the subsoil layer was in more iron-manganese spots and poor structure.Furthermore,the soil infiltration parameters decreased with the increasing pit depth.The average infiltration rate and cumulative infiltration in the 0-15 cm pit depth range were 17.04 and 18.06 times higher,respectively,than those in the>20-30 cm pit depth range.The three infiltration models were fitted using Horton,Kostiakov and Philip.Specifically,the Kostiakov model had the highest R^(2)(0.98-0.99)and the smallest root mean square error(0.01-0.77 mm/min),indicating the consistency of the fitted parameters.Infiltration parameters were extremely significant correlated with the soil bulk density,water content,total porosity,and field capacity(P<0.01),but not with the soil penetration resistance(P>0.05).Field in situ infiltration experiment at different depths was an important tool to identify the soil stratification and quantify the water function differentiation in the soil profiles,according to the soil profile,cone penetration and sampling.Long-term mechanized tillage under the smallholder production model in the rice-wheat rotation region of eastern China can be expected to result in the apparent stratification and vertical differentiation of soil water functions in paddy soils.In turn,there are also some significant differences in the infiltration capacity between the cultivated layer and soil layers below the cultivated layer.This study can provide a reference for mechanical cultivation and irrigation in rice-wheat rotation regions.