| Dry-land with purple soil concentrated in the Sichuan basin accounts for 51.28% of China’s total, of which the total area is 18.891 million hm2. The purple soil behaves fast soil forming, high cultivation and productivity, but it also shows high erosion, poor drought resistance and servious soil degradation. Slope farmland in purple soil hilly area is the main agricultural production area in Sichuan province and Chongqing city. However, under the comprehensive function of the natural factors(rainfall, topography,etc) and artificial factors(cultivation, fertilization,etc), soil degradation, land productivity decrease, and non-point source pollution ecological problems on slope farmland with purple soil is very prominent, and serious soil and water loss of slope farmland also resulted in non-point source pollution serious increasingly. The cultivated-layer soil is not only the object of soil erosion on slope farmland, but also the basic condition to ensure high and stable crop yield. The profile structure and physical and chemical properties of cultivated-layer soil is the root cause of soil quality and the important factor comprehensivly reflecting soil fertility; the important condition to ensure regional food security and ecological security is: 1) understand cultivated-layer quality variation, 2) clear its obstacles, 3) strengthen the effective management, 4) improve the quality of cultivated-layer on slope-farmland.Taking the cultivated-layers of slope-farmland in purple hilly area with high and low yield as the research object, this paper analyzed farmland distribution and quality evolution process in Chongqing, and revealed the function characteristic of planting system, rainfall, cultivation and other driving forces in cultivated-layer quality evolution process through field investigation and data access; the paper analyzed the differences of profile structure, soil physical properties and soil nutrient content of cultivated-layer of slope-farmland, and reveal the structure characteristics of cultivated-layer profile through field investigation and laboratory test; the paper analyzed water storage capability of the cultivated-layers with different crop by using the interior ring knife infiltration method; the paper studied soil retaining property of cultivated-layer by dry-sieving and wet-sieving method. The paper analyzed the crop—cultivated-layer degree of coupling coordination on and evaluated the suitability of cultivated-layer on slope-farmland by constructing the crops—cultivated cultivated-layer coupled coordination model. The main conclusions are as follows:(1) The slope level and soil fertility grade of slope-farmland in the four regions of soil and water conservation in Chongqing was significantly different. The slope farmland in Chongqing centralized in two grades of 6-15° and 15-25°. The area proportion of slope farmland in 6-15° degree in its’ area ranged in such order as soil conservation region of Sichuan Basin in the southern low hilly(53.81%) >soil habitat environment maintenance preserving region in Sichuan parallel ridge and valley mountain(49.86%)>water conservation and soil conservation region in e Yu mountain(41.37%)>soil ecological protection preserving region in Daba Mountains(34.66%); The area proportion of soil fertility level in different areas was significantly different, which in soil ecological protection preserving region in Daba Mountains was changed in third-class>fourth-class>second-class>fifth-class>first-class, the proportion were 36.367%, 28.034%, 19.510%, 10.821% and 5.269%, respectively; there was the same changing trend in water conservation and soil conservation region in e Yu mountain; but the distribution proportion changed in such order as fourth-class(32.129%)>third-class(27.313%)>fifth-class(22.735%)>second-class(13.892%)>first-class(3.931%) in soil conservation region of Sichuan Basin in the southern low hilly, which in soil habitat environment maintenance preserving region in Sichuan parallel ridge and valley mountain varied in the same trend.(2) The soil organic matter content of slope farmland in different soil and water conservation regionalization of Chongqing, showed grater regional difference under the comprehensive effects of natural factors and artificial factors. In each division unit, the organic matter increasing proportion of farmland soil was in such order as soil conservation region of Sichuan Basin in the southern low hilly(12.85%)>water conservation and soil conservation region in e Yu mountain(11.55%)>soil ecological protection preserving region in Daba Mountains(10.38%)>soil habitat environment maintenance preserving region in Sichuan parallel ridge and valley mountain(6.38%). Furthermore, the content of nitrogen and phosphorus of farmland soil also showed increasing trend in different degrees. The phenomenon of soil acidification in farmland is common in different degrees in Chongqing, and the variation coefficient of soil pH value in farmland distributed in-15.66% ~-1.27%. Different tillage methods and protective measures have different effects on the soil water heat and nutrients, and the reasonable management measures could improve the soil physicochemical properties and soil quality of cultivated-layer, which leaded to yield increase.(3) The profile structure, particle composition and physicochemical properties of cultivated-layer(0-20cm) on different slope-farmland with purple different yields, were different significantly. The profile structure of cultivated-layer on slope-farmland was mainly loose or less loose, of which the compaction was5.31~8.46kg/cm2 and with a variety of granular, granular structure and crop roots distributed in large quantities. The soil compaction of cultivated-layer with high yields were lower than that of the low one, which cultivated with corn and tobacco reduced by 32.1% and 9.11% by compared with their low yield one. The soil bulk density increased with the increase of cultivated-layer depth, which with high corn yield reduced by 8.83%, 13.80% and 3.50% by compared with its’ low yield one, and with high tobacco yield reduced 7.44%, 17.86%, 14.11%. The soil organic matter content of cultivated-layer varied in the order of cultivated-layer with high corn yield(15.30 g·kg-1)>cultivated-layer with high tobacco yield(14.80g·kg-1)>cultivated-layer with low tobacco yield(14.30 g·kg-1)>cultivated-layer with low corn yield(11.80 g·kg-1), and the soil total nitrogen content changed in the same trend. The cultivated-layer with low yield has low coverage and greater slope, which leaded to high nutrient attenuation degree under rainfall. The research showed that cultivated-layer profile with yield on slope-farmland with purple soil showed higher organic matter and nutrient content, loose soil. Whtat’s more, the soil texture and soil compaction is the main factor affecting soil profile structure performance.(4) The soil infiltration capacity of different cultivated-layer on slope-farmland and its’ various depth was significantly different. The soil stable infiltration rates of 0-20 cm, 2-40 cm and 40-60 cm cultivated-layer with purple soil were 5.80-9.58 mm/min, 2.81-4.35mm/min and 0.98-1.96mm/min. The cumulative infiltration decreased linearly with the increase of cultivated-layer depth, which of 20-40 cm and 40-60 cm cultivated-layer with high corn yield were 84.85% and 91.63% less than that of 0-20 cm, that with high tobacco yield were 78.54% and 86.85% lower than its’ 0-20 cm, and this infiltration capacity was conducive to soil water storage. The initial soil infiltration rates of 0-20 cm, 2-40 cm and 40-60 cm cultivated-layer with high corn yield were 70.95%, 2.62%, 19.20% more than that with low yield, the steady infiltration rate increased by 65.17%, 35.59%, 77.55% over the low one; while the initial infiltration rates with high tobacco yield decreased by 14.94%, 20.53%, 20.39% over that with low yield, and the stable infiltration were 32.90%, 52.10%, 7.69% more than that with low yield, which indicated that low soil porosity and greater soil bulk density of cultivated-layer leaded to the low water permeability and retention property.(5)The soil aggregates and dynamics stability of different cultivated-layer on slope-farmland was significantly different. The stable index of 0-20 cm cultivated-layer varied in such order as cultivated-layer with high tobacco yield(HT)(2.96)>cultivated-layer with high corn yield(HC)(2.55)>cultivated-layer with low tobacco yield(LT)(2.45)>cultivated-layer with low corn yield(LC)(2.38), and soil shear strength changed in the order as LC(36 Kpa)>HC(29 Kpa)>LT(25 Kpa)>HT(21Kpa), and soil penetration resistance varied in the order as LC(1.8Mpa)>HC(0.95Mpa)>LT(0.7Mpa)>HT(0.4Mpa),The soil aggregate composition of cultivated-layer concentrated in three fractions grades of > 5 mm, 5~3 mm and 1~0.5 mm, and mechanical stable aggregates content of> 0.25 mm distributed in 41.50-89.71%, which decreased with the increase of cultivated-layer. The stable aggregates of 1~0.5 mm and 0.5~0.25 mm increased after wet-seived, that in grades of > 5 mm, 5~3 mm and 3~2 mm decreased significantly; water-stable aggregates in grades of > 1 decreased with the increase of cultivated-layer depth significantly, which of 20-40 cm and 40-60 cm of cultivated-layer with high corn yield were 20.99% and 37.52% lower than that of 0-20 cm, and that with high tobaccon yield decreased by 15.18%, 24.89%, respectively. The soil shear strength and penetration resistance of cultivated-layer increased first then decreased sharply with the increase of depth, of which the peak value appeared in 20~40 cm and 40~50cm, respectively. Tests show that cultivated-layer with high yield on slope-farmland of purple soil reflected these features:1) high content of mechanical stable and water stable aggregate, 2) lower soil shear strength and penetration resistance. Furtheremore, the soil organic matter content, soil compaction and bulk density were main factors of soil conservation ability and cultivation ability of cultivated-layer.(6)The study defined interval and divided type of crop—cultivated-layer coupling coordination degree by using evaluation model of crop—cultivated-layer coupling coordination degree. The comprehensive weights of canopy density, species number, biological yield and economic yield index values in CCE were 0.0739, 0.0345, 0.1832 and 0.7084, respectively. The comprehensive weights of the field surface slope, topsoil thickness, soil bulk density and soil texture comprehensive weight value in the PCE were 0.1055, 0.1533, 0.1742, 0.1013, and which of the pH, organic matter, total nitrogen, available phosphorus and available potassium comprehensive weight value were 0.0561, 0.1334, 0.1079, 0.0832 and 0.0852, respectively. The study divided crop—cultivated-layer coupling coordination types into four major categories and ten kinds of types, namely imbalance decline(0-0.2), on the verge of disorders(0.2-0.5), the basic coordination(0.5-0.7) and high coordination(0.7-1.0). The research divided poor profile of cultivated-layer in slope-farmland with purple soil into 5 kinds as sand homogeneous type, clay homogeneous type, thin-layer type, bottom sand leakage type and clayey soil mingled with sand type. The shallow value of cultivated-layer in slope-farmland with purple soil increased with the increasing erosion degree, and resistance ability to seasonal drought decreased with the soil depth. By comprehensivly analyzing field investigation and experiment, the reasonable cultivated-layer in slope-farmland with purple soil mainly showed these factors as cultivated-layer depth >60cm, soil bulk density with 1.10~1.25g/cm3, soil texture with loam or sandy loam, soil structure with loam-clay-loamy clay type, or loam homogeneous type, soil shear strength with 12.5~68.0Kpa, soil organic matter content more than 2.5%. |
PDF Full Text Request