Liming Decreases the Vertical Mobility of Potassium in Acidic Soils

Liming increases soil negative charges and thus affects the chemical equilibrium of cations between the solid phase and the soil solution with consequences for the mobility of cations. The effects of lime and potassium chloride (KCl) addition on the vertical movement of potassium (K), calcium (Ca), and magnesium (Mg) were investigated in two Brazilian soils. The experiment was carried out in leaching columns. Treatments included a combination of rates of KCl (0, 50, 100, and 200 mg kg^?1 K) and acidity levels (without and with liming). Seven water percolations (400 mL per column) were performed at weekly intervals, totaling an equivalent to 357 mm of rain. Raising the soil pH decreased the leaching of K, in both soils, up to 50% because of the increase of its electrostatic adsorption on created negative charges. Addition of KCl increased the percolation of K, Ca, and Mg proportionally to the rate applied, and it was more efficient than calcium carbonate to percolate Ca in both soils. Liming must be taken into consideration when K leaching or plant needs of K are estimated in predominantly variable-charge soils.     

江西省雨水、灌溉水及渗漏水中的硫对土壤硫的影响

Ten rainfall and irrigation water-collecting posts were set up in different ecotype districts of Jiangxi Province,China,to quarterly measure S content in rainfall and irrgation water.A rasinwater chemical composition-collecting device was used to collect the sulphur in rainfall,and the amount of sulphur adsorbed on the resin column in the device was determined.The soil percolating water was gathered using 6 lysimeters built up according to the profile sequence of the red soil derived from red sandstone and the red soil derived from Quaternary red clay,separately.On the lysimeters peanuts,soybean and radish were grown in rotation.Two treatments were designed:without S addition and with S additin at a rate of 14kg S ha^-1,The SO4^2- contents in rainfall,irrigation water and soil percolating water were determined by the turbidimetry.The results in 1997 showed that the average annual S content in rainwater ws 28.13kg S ha^-1.the average S content in irrigation water was 1.7mg S L^-1,and the average content of SO4^2- in soil percolation water was 2.30kg Sha^-1 year^-1 and 4.70 kg Sha^-1 year^-1 in treatments without and with sulphur application,respectively,In Jiangxi Province,apart from the losses by runoff and leaching,the sulphur in rainfall avaliable to crops is 7.3kg S ha^-1 year^-1 and additional S application is required.When rice is grown.however,irrigation water can suply 6.9kg S ha^-1,which,along with the sulphur in rainfall,cal almost meet the S requirement of one cropping of rice.     

The effect of soil moisture on the vertical movement of rock fragments by tillage

Chiselling in air-dry soils can rapidly create inverse grading of the plough layer as field experiments showed, i.e., the largest particles (rock fragments) are brought to the surface and the smallest particles concentrate at the bottom of the plough layer. Since no information about the effect of soil moisture and fine earth characteristics on this process is available laboratory experiments were conducted to examine the effect of soil moisture and fine earth characteristics on the vertical movement (segregation) of rock fragments due to tillage. An experimental trough, 120×60×40 cm³, was filled with three layers (each 4 cm thick) of fine earth (sand or silt loam), and rock fragments (1.2–2.2 and 2.7–4.0 cm). Tillage was simulated by moving a hand-held cultivator through the mixture. The results for the sandy soil matrix showed that inter-particle percolation was slowed down by soil moisture, however, at the same rate for different moisture levels. This was attributed to water-films that surround the sand particles. In the silt-loam soil matrix inter-particle percolation was stronger than that occurring in the sandy matrix at similar volumetric moisture contents but vertical movement was impossible at higher moisture contents (0.17 m³ m⁻³) because of a strong increase in stickiness. The results imply that at low moisture contents farmers in areas threatened by desertification can use moderate tillage as a means to create a surface rich in rock fragments which helps to increase water infiltration and decrease erosion.     

W-OH固化剂对土壤水渗漏及硝态氮淋失的影响

采用盆栽试验结合天然降雨观测,研究了不同W-OH喷施浓度(1%、3%和5%)对作物(大豆、玉米和大蒜)地土壤水渗漏及硝态氮淋失的影响。结果表明:本试验条件下W-OH的保水作用受降雨量和作物类型影响;小雨和中雨条件下,玉米地土壤水渗漏量随W-OH施用浓度的增加呈先减小后增加,浓度为3%的处理渗漏量最低,保水效益明显;当降雨量达大雨及以上级别时,W-OH的保水作用与其喷施浓度成正比;W-OH对大豆和大蒜地的保水作用不受降雨量的影响,且其对二者土壤水渗漏量的影响规律相似,与对照(不喷施WOH)相比,各处理水分渗漏量随W-OH浓度增加而增加。在作物生长初期,W-OH的保肥作用与其施用浓度成正比,经历后续降雨渗流多次淋溶,保肥作用趋于稳定;玉米和大蒜地喷施中、高浓度(3%和5%)的WOH即可减少硝态氮淋失量,大豆地1%浓度的W-OH即可减少硝态氮淋失。