Response of CH_4 emission of paddy fields to land management practices at a microcosmic cultivation scale in China

The terrestrial ecosystem may be either a source or a sink of CH_4 in rice paddies, depending, to a great extent, on the change of ecosystem types and land use patterns. CH_4 emission fluxes from paddy fields under 4 cultivation patterns (conventional plain culture of rice(T1), no-tillage and ridge culture of rice(T2), no-tillage and ridge culture of rice and wheat (T3), and rice-wheat rotation(T4)) were measured with the closed chamber technique in 1996 and 1998 in Chongqing, China. The results showed that differences existed in CH_4 emission from paddy fields under these land management practices. In 1996 and 1998, CH_4 emission was 71 48% and 78 82%(T2), 65 93% and 57 18%(T3), and 61 53% and 34 22%(T4) of that in T1 during the rice growing season. During the non-rice growing season, CH_4 emission from rice fields was 76 23% in T2 and 38 69% in T1 The accumulated annual CH_4 emission in T2, T3 and T4 in 1996 decreased by 33 53%, 63 30% and 65 73%, respectively, as compared with that in T1 In 1998, the accumulated annual CH_4 emission in T1, T2, T3 and T4 was 116 96 g/m^2, 68 44 g/m^2, 19 70 g/m^2 and 11 80 g/m^2, respectively. Changes in soil physical and chemical properties, in thermal and moisture conditions in the soil and in rice plant growth induced by different land use patterns were the dominant causes for the difference in CH_4 emission observed. The relative contribution of various influencing factors to CH_4 emission from paddy fields differed significantly under different land use patterns. However, the general trend was that chlorophyll content in rice leaves, air temperature and temperature at the 5 cm soil layer play a major role in CH_4 emission from paddy fields and the effects of illumination, relative humidity and water layer depth in the paddy field and CH_4 concentration in the crop canopy were relatively non-significant. Such conservative land use patterns as no-tillage and ridge culture of rice with or without rotation with wheat are thought to be beneficial to reducing CH_4 emission from paddy fields and are, therefore, recommended as a significant solution to the problems of global(climatic) change.

SUSTAINABLE LAND USE PLANNING BASED ON ECOLOGICAL HEALTH——Case Study of Beiwenquan Town, Chongqing, China

This paper, taking Beiwenquan Town of Beibei, Chongqing as an example, assessed the impacts of land use on ecological health by comprehensive index method, and discussed methodological system of sustainable land use planning based on ecological health. Results indicated that: 1) From 1992 to 2002, land use changes focused on 12 patterns with the total conversion area of 92.11%, which were related to cultivated land, residential and industrial-mining area, and orchard land. Urbanization and economic reconstruction were the leading driving forces. 2) There was obvious difference of the areas of ecotypes driven by land use change in wide valley and mild slope between 1992 and 2002, while there were little or no difference in steep slope and very steep slope. 3) Both of the conditions of ecological health in 1992 and 2002 were sound, and the ecotypes focused on the types of health and sub-health. But, health ecosystem in 1992, with an area of 764.64ha, accounting for 38.51% of the total evaluation area, was better than that in 2002, with an area of 636.10ha, accounting for 34.19% of the total evaluation area. 4) The ecotypes involved into different ranges have already degenerated, due to humankind’s disturbance, while the conditions of ecological health in the same ranges in 1992, regardless of stability and reconstruction, were better than that in 2002. 5) The planning scenario based on ecological health was accorded with the practice condition of Beiwenquan Town: 388.29ha of cultivated land could meet the Beiwenquan demand of food and byproduct; 1045.26ha of forest land area, the Beiwenquan demand of ecological health; and 1004.73ha of the residential and industrial-mining area, the Beiwenquan building demand. 6) Sustainable land use planning based on ecological health had higher useful value, because it not only stood to ecological theory, but also satisfied the developmental demand of society and economy.

Soil NH_4^+ Fixation and Fertilizer N Recovery as Affected by Soil Moisture and Fertilizer Application Methods

Ammonium fixation and the effects of soil moisture and application methods on fertilizer N recovery were investigated in two soils of Shaanxi Province,China,a Luvisol and an Entisol,through two experiments performed in the laboratory and in a glass shelter,respectively,by using ammonium bicarbonate (NH4HCO3). The laboratory closed incubation box experiment was conducted using the Luvisol to study NH4+ fixation rate at soil moisture levels of 10.1%,22.7% and 35.3% water filled pore space (WFPS). The fixed NH4+-N increased dramatically to 51% and 66%,67% and 74%,and 82% and 85% 1,2 and 36 h after fertilizer incorporation at moisture levels of 10.1% and 22.7% WFPS and 35.3%WFPS,respectively. The rapid NH4+ fixation rates at all moisture levels could help prevent NH4+ losses from ammonia volatilization. In the glass shelter pot experiment,N fertilizer was applied by either banding (in a concentrated strip)or incorporating (thoroughly mixing) with the Entisol and the Luvisol. An average of 74.2% of the added N fertilizer was recovered 26 days after application to the Luvisol,while only 61.4% could be recovered from the Entisol,due to higher NH4+ fixation capacity of the Luvisol. The amount of fixed NH4+ decreased with increasing WFPS. The amount of fixed NH4+ in the incorporated fertilizer treatment was,on average,10% higher than that in the banded treatment.Higher NH4+ fixation rates could prevent N loss and thus increase N recovery. The results from the Luvisol showed lower nitrogen recovery as soil moisture level increased,which could be explained by the fact that most of the fixed NH4+ was still not released when the soil moisture level was low. When the fertilizer was incorporated into the soil,the recovery of N increased,compared with the banded treatment,by an average of 26.2% in the Luvisol and 11.2% in the Entisol,which implied that when farmers applied fertilizer,it would be best to mix it well with the soil.

Physiological Characterization of Zn-efficient Rice (Oryza sativa) Genotype at Different Zn^(2+) Levels

Physiological characteristics of rice at different Zn^(2+) levels[pZn^(2+)>11.5, 11.3, 11.0, 10.6, 10.3, 9.7] were studied with the Zn-efficient rice cultivars IR34, IR36, IR8192, and Zn-inefficient rice cultivars IR26, Ce 64-7, Biyuzaonuo, which grew in chelator-buffered nutrient solution. There were significant differences in tolerance to zinc deficiency among different rice genotypes. Obvious effects of low zinc activity on the physiological characteristic of rice seedlings were noted. There were significant differences in chlorophyll content, photosynthesis rate, MDA concentration in rice leaf, and H^+ excretion of root. As pZn^(2+) decreased, chlorophyll content and photosynthesis rate decreased at a slower pace in Zn-efficient cultivars compared to Zn-inefficient ones, MDA concentration increased slower while H^+ excretion of root increased faster in Zn-efficient cultivars than those in Zn-inefficient ones. It was suggested that the above indications could be used as indexes to Zn-efficiency of rice.

Phosphorus Nutrient Characteristics of Different Maize (Zea mays L.) Inbreds for Tolerance to Low-P Stress

Phosphorus nutrient characteristics of different maize inbred lines to low-P stress were studied at stages of seedling, steming, earing, silking under pot culture. In the periods of seedling and steming, P uptake efficiency was the main contributor to P tolerance, and the relative P content in P-tolerant genotypes, 99180 and 99239 were higher than that in sensitive genotype, 99152. At earing stage, P-tolerant genotypes, compared to P-sensitive ones, had higher accumulation of P in upper leaves. When came to the silking stage, P uptake and redistribution efficiency of P-tolerant genotypes were higher than those in 99152. The results also suggested that there are different mechanisms of P nutrient uptake and distribution in different P-tolerant genotypes. Inbred line 99239, according to the investigation, was considered as an efficient stock in the P-uptake while 99180 fallen to the efficient stock of P redistribution.

Effect of Humus on Activity of Mineral-Bound Hg: III.Effect on Leachability and Transfer of Mineral-Bound Hg Under Acid Leaching Condition

Effects of humus fractions (fulvic acid, brown humic acid and grey humic acid) on the leachability and transferring activity of five types of mineral-bound Hg were investigated. Under the acid leaching condition: fulvic acid could promote leachability and vertical transference of all the mineral-bound Hg. Brown humic acid could retard the leaching and transferring processes of CaCO3-Hg, Fe2O3-Hg, MnO2-Hg and kaolinite Hg but not bentonite-Hg. Grey humic acid could greatly enhance residing ability of the mineral-bound Hg in the soil column and restrain them from vertical transferring. The effect of humus on leachability and transferring activity on the mineral-bound Hg was closely related to its ability to convert the mineral-bound Hg into organic-bound form and the transferability of the latter in the soil column. The characteristics of the mineral-bound Hg in speciation were the internal factors that determined the extent and rate of the influence of the humus.

Plateau Marsh Methane Oxidation as affected by Inorganic N

In a series of laboratory incubations using soils of two contrasting sitesfrom a temperate marsh on the Qinghai-Tibet Plateau, potential methane (CH_4) oxidation rates weremeasured to study the effects of inorganic N inputs on CH_4 oxidation. For adrained site, subsurfacepeat (5--15 cm) at an initial 20 mu L CH_4 L^(-1) showed a significantly different (P < 0.05) CH_4oxidation rate compared to other soil depths, with a maximal rate of 20.9 ng CH_4 gDW (dryweight)^(-1) h^(-1); the underlying mineral soil layers (15--30 and 30--50 cm) also had a strongCH_4 oxidation capacity at about an initial 2 000 mu L CH_4 L^(-1). With a waterlogged site, theCH_4 oxidation rate in an aerobic incubation was significantly greater (P < 0 05) in the surfacesoil layer (0--5 cm) compared to the 15--30 and 30--50 cm depths. There was generally no or a veryweak effect from addition of NO_3^- on CH_4 oxidation. In marked contrast, NH_4^+ salts, such as(NH_4)_2SO_4, NH_4Cl and NH_4NO_3, exhibited strong inhibitions, which varied as a function of theadded salts and the initial CH_4 level Increasing NH_4^+ usually resulted in greater inhibition andincreasing initial CH_4 concentrations resulted in less NH_4^+ inhibition on CH4 oxidation innatural high-altitude, low-latitude wetlands could be as important as has been reported foragricultural and forest soils. The NH_4^+ effects on the CH_4 oxidation rate need to be furtherinvestigated in a wide range of natural wetland soil types.

Assessment on Carbon Sequestration Benefit of Fast-growing and High-yielding Forest Base Construction Program

Fast-growing and High-yielding Forests Base Construction Program is the only industrialization program of six key forestry programs. The main construction content is to plant 13.33 million hm fast-growing and high-yielding plantation in 18 provinces in China. According to the program planning and growth of different tree species, the biomass of this program is evaluated and the C sequestration is assessed in this paper. In the program period, the biomass of the program will reach 3.703 6×109 t, and the C storage will get 1.851 8×109 t. The program will have a great effect on raising the C pool function of forest vegetation.

Regional Evaluation of Wind Erosion of the Loess Plateau in Pengyang County,Ningxia Hui Autonomous Region,China

The loess plateau in China is well-known for its severe water erosion. A nationwide soil erosion survey discovered that wind erosion of the loess land is also greatly concerned. The severity of wind erosion for each land use in Pengyang County of Ningxia Hui Autonomous Region, China, was evaluated according to the national standard of soil erosion classification. The evaluation system includes a GIS database, an evaluation indicator system and a classification system for land and land use. The erodible nature of soil and annual soil loss of the most erodible land were obtained as follows: (1) Croplands plowed and harrowed in late autumn were the most erodible land,with an erosion intensity of medium grade and an erodible proportion of 46%; (2) The erodible proportion of natural grasslands was between 19.3% and 21.5%, whose erosion intensity was of mostly tolerable grade; (3) When it came to the whole county, there was 21.3% of the total area in tolerable grade in terms of wind erosion intensity, 42.1% slight and 34.8% medium.

Sustainable Factors Analysis of Restored and Rebuilt Ecosystem

This study compared the paddy field ecosystem on developped from basalt area in Jingpo Lake with primary ecosystem by analyzing some indexes such as sunlight, temperature, moisture, biodiversity and energy. The result indicate that the paddy field ecosystem is feasible in improving the environment, energy utility, biodiversity and economy. And also it is a sustainable system, providing theoretical basis and practical reference for the rebuilt of similar system.