A chronosequence study of purple paddy soils with respect to improving ammonium and potassium fertilization management

Journal of Soils and Sediments - Purple paddy soils cover about 66% of the paddy soils in Sichuan Basin. Complex interactions made the effects of potassium fertilizer application on NH4+ adsorption...     

中国亚热带森林小流域植物生长驱动下矿物风化评估

Plant growth contributes to mineral weathering, but this contribution remains poorly understood. Weathering rates in an aggrading forested watershed in subtropical China were studied by means of geochemical mass balance. Rainfall, dry deposition, and streamwater were monitored from March 2007 to February 2012. Samples of vegetative components, rainfall, dry deposition, streamwater, representative soils, and parent rock were collected and determined for mass balance calculation and clarifying plant-driven weathering mechanisms stoichiometrically. Ignoring biomass, weathering rates of Ca²⁺, Mg²⁺, Na⁺, and Si were 25.6, 10.7, 2.8, and 51.0 kg ha^-1 year^-1, respectively. Taking biomass into consideration, weathering rates of Ca²⁺, Mg²⁺, and Si and the sum of weathering rates of Ca²⁺, Mg²⁺, Na⁺, K⁺, and Si were 2.6, 1.8, 1.2, and 1.5-fold higher than those ignoring biomass, respectively. This is attributed to plant-driven weathering due to the nutrient (e.g., Ca²⁺, Mg²⁺, and K⁺) absorption by vegetation and substantial proton production during assimilation of these nutrients, with the former acting as a pump for removing weathering products and the latter being a source of weathering agents solubilizing mineral components. The same pattern of weathering, i.e., higher rates of weathering with than without including biomass in mass balance calculation, was reported in previous studies; however, the extent to which plants drive weathering rates varied with vegetation types and climatic zones. The documented biological weathering driven by plants is expected to play a critical role in regulating nutrient cycling and material flows within the Earth’s Critical Zone.     

长期种植苜蓿对中国半干旱地区黄土钾含量和粘土矿物的影响

Alfalfa cropping has been considered an efficient method of increasing soil fertility.Usually nitrogen increase in root nodules is considered to be the major beneficial effect.A 21-year time series (five sampling periods) of alfalfa cultivation plots on a loess soil,initially containing illite and chlorite,in Lanzhou of northwestern China was selected to investigate the relationships among alfalfa cropping,soil potassium (K) content and soil clay minerals.The results indicated that soil K significantly accumulated after cropping,with a peak value at about 15 years,and decreased afterwards.The accumulated K was associated with the K increase in the well-crystallized illite,which was not extracted by the traditional laboratory K extraction methods in assessing bioavailability.The steep decline in soil K content after 15-year cropping was in accord with the observed fertility loss in the alfalfa soil.Plant biomass productivity peaked at near 9 years of culture,whereas soil K and clay minerals continued to increase until cropping for 15 years.This suggested that K increased in the topsoil came from the deep root zone.Thus alfalfa continued to store K in clays even after peak production occurred.Nitrogen did not follow these trends,showing a general decline compared with the native prairie soils that had not been cropped.Therefore,the traditional alfalfa cropping can increase K content in the topsoil.     

Potassium supply capacity response to K-bearing mineral changes in Chinese purple paddy soil chronosequences

Purpose

Purple paddy soils are important for food production. Their potassium (K) supply capacity affects rice yields through its effect on nutrient availability. We hypothesize that changes in soil mineralogy can influence the K supply capacity and the efficiency of K fertilizer. Designing management practices that optimize crop yield while minimizing environmental impacts is a major challenge in agriculture. For this, it is necessary to understand the evolution of, and interaction of, minerals and different chemical forms of K in the soil system.

Materials and methods

Taking advantage of the long-term paddy cultivation history in China, two purple paddy soil chronosequences, one in Guang’an, Sichuan Province (P sequence) and the other in Longsheng, Guangxi Autonomous Region (PS sequence) in Southwest China, were investigated.

Results and discussion

Depotassification is prevalent in both paddy soil chronosequences, which is consistent with the decrease of illite and K-feldspar in the P sequence and with the decrease of muscovite in the PS sequence. K-bearing primary minerals are the long-term stable source of non-exchangeable K (interlayer K) in both chronosequences. Illite in clay fractions acts as the main sources of non-exchangeable K in the P sequence. In contrast, clay minerals derived from muscovite are the main sources of non-exchangeable K in the PS sequence. Clay mineral authigenesis is an important process in the purple paddy soils rich in K-bearing minerals.

Conclusions

The changes in mineralogy of purple paddy soils do not conform to the usual sequence found in the well-drained natural soils. Artificial submergence promotes the conversion of mineral K (lattice-bound K) to non-exchangeable K and enhances the availability of mineral K. The disintegration of K-bearing primary minerals thus controls the K supply capacity in purple paddy soils.

     

Transmission dynamics of the etiological agent of SARS in Hong Kong: impact of public health interventions

We present an analysis of the first 10 weeks of the severe acute respiratory syndrome (SARS) epidemic in Hong Kong. The epidemic to date has been characterized by two large clusters-initiated by two separate "super-spread" events (SSEs)-and by ongoing community transmission. By fitting a stochastic model to data on 1512 cases, including these clusters, we show that the etiological agent of SARS is moderately transmissible. Excluding SSEs, we estimate that 2.7 secondary infections were generated per case on average at the start of the epidemic, with a substantial contribution from hospital transmission. Transmission rates fell during the epidemic, primarily as a result of reductions in population contact rates and improved hospital infection control, but also because of more rapid hospital attendance by symptomatic individuals. As a result, the epidemic is now in decline, although continued vigilance is necessary for this to be maintained. Restrictions on longer range population movement are shown to be a potentially useful additional control measure in some contexts. We estimate that most currently infected persons are now hospitalized, which highlights the importance of control of nosocomial transmission.