Abstract:This article deals with the structural characteristics of the fertile paddy soils in the southern region of Kiangsu province. Pre liminary experiments show that the bulk density of the arable soil-layer in wheat-planting season attains<1.20 gm.cm^-3,total soil porosity<55% (V),non-capillary porosity>5% (V),compressive strength of airdry soilclods 26-30 kg·cm^-2. The correlation between the compressive. strength of soil clods and the quantity of the clay particles(<0.001mm) on the one hand and the physical clay particles on the other is significantly positive,while the quantity of non-capillary porosity is negative. The correlation between the compressive strength and quantity of organic matter and total porosity of soils is nonsignificant.

Abstract:For the purpose of,characterizing the water-soluble ferrous iron in paddy soils,the iron was determined as metal ions and those complexed by organic matter separately. A certain amount of a-a' dipyridyl solution was added to the water extract,and the color intensity was measured at different time intervals. Maximum color intensity was usually obtained after 48 hours. The amount of iron corresponding to the respective color intensity was plotted against the logarithm of rime in seconds,and the extrapolated intersection at zero time was taken as the metal ions. The amount of compleged iron was calculated as the difference between the amounts of total ferrous iron and that of metal ions.

Abstract:The influence of geological and geomorphological factors on the nature,properties,classification and distribution of forest soils and on tree growth in the low mountain and hill regions of Kiangsu is discussed. Some great soil groups such as the fossil red eartlx (paleudult),the claypan soil (planosol),the skeletal soil (lithosol),the dark basic,soil (relating to andosol),the rendzina and the. vadose soil were tentatively elassified in accordance with the differences in structural features of rocks,geomorphological types,properties of rocks and the Quarternary deposits,which reflected on soil profiles.

Abstract:The precipitation is known as the main source of water for the planosol (a bleached soil). According to the nature of the soil moisture regime,the annual moisture cycle of the planosol may be divided into two periods,i. e. the frozen period and the crop growth period at summer and autumn. These two periods can be also subdivided into five phases. The former period involves two phases:the freezing and thawing of the sail,while the latter period contains three phases:lower moisture in early-summer;an excess of soil water in mid-siunmer and a humid soil condition in late-autumn.

Abstract:Field observations and plot experiments revealed that a well developed plowed layer promoted the rate of desalinization of soils during the rainy season owing to its good permeability. While at the dry season,it facilitated the rate of evaporation of soil moisture and formed a dry mulch of a few em thick. The mulch reduced the rise of ground water from subsoil horizons and consequently kept the soil in a desalinized condition for a longer period. In a well cultivated soil,the annual rate of desalinization attained 30-50% within 1 meter in soil profile.

Abstract:Azolla is a common green manure used in paddy soils in eastern and southern China. Its effect on the growth of rice plant and the physical properties of soil was studied both in field experiment and pot culture. Results revealed that the contribution of available nitrogen from Azolla was lower than that of milk vetch but rather higher than compost. Azolla as a green manure,however,accumulated more organic matter in soils than the milk vetch and consequently manifestf}d more favourable effect on the improvement of soil physical properties in well drained conditions. Through two years observation,it was found that the rate of decomposition of Azolla in soils was comparatively slower than milk vetch and rice straw. But A.zolla,as well as other manures,gave no effects on the improvement of permeability in poorly drained paddy soils.

Abstract:The potassium contents of various soils in Kiangsu differ greatly. Analysis of more than seven hundred representative soil samples selected from different parts of the Province showed that the contents of available K (1N NH₄,OAc extractable) in soils ranged 4.8-32.0 mg K₂O/100 g soil,slowly available K (soluble in boiling 1N HNO₃) 20.9-145.1 mg K₂O/100 g soil,and the total,K₂O 1.41-2.67% (for detailed informations refer to table 1 in the Chinese text).It was found that the parent materials and their degree of weathering,and soil texture have coused such differences.

Abstract:Ammonium bicarbonate,still being one of the main nitrogen fertilizers at present time in China,is easily volatilizable in soils. Various field experiments as well as practices have repeatedly shown that,if prilled and applied beneath the soil surface about 6 cm,its effect on the growth of crops will be markedly increased. In order to get some idea about the mechanism involved in its beneficial effect,the present study was undertaken.Experiments were carried out in pots under greenhouse conditions as well as in the paddy field using N¹⁵-tracer technique.The following is a summary of the results.

Abstract:It is generally known that in order to make the stiff clay gradually become chessom,we can make use of green manure to bring into practice the reclamation of physico-chemical properties of soil,the decrease of bulk density and resistance to compression of soil and the increase of porosity,moisture capacity and aggregation of soil. In addition,application of green manure evidently accumulates some additional organic matter and nitrogen contained in the soil.It should be noted that the response of rice productivity on mixed cropping of vetch-rye grass used as green manure is much better than vetch alone.

Abstract:The present paper. deals with mainly the drainage problem of the soils in the suburbs of Shanghai. The soils are mostly used under a rotation system of wheat (hull-less barley)-rice annually. Excess content of soil moisture usually restricts the growth and yield of winter crops. Various ameliorative measures for the improvement of drainage condition of soils are described.