Impacts of LUCC processes on potential land productivity in China in the 1990s

Using meteorological data and RS dynamic land-use observation data set, the potential land productivity that is limited by solar radiation and temperature is estimated and the impacts of recent LUCC processes on it are analyzed in this paper. The results show that the influence of LUCC processes on potential land productivity change has extensive and unbalanced characteristics. It generally reduces the productivity in South China and increases it in North China, and the overall effect is increasing the total productivity by 26.22 million tons. The farmland reclamation and original farmlands losses are the primary causes that led potential land productivity to change. The reclamation mostly distributed in arable-pasture and arable-forest transitional zones and oasises in northwestern China has made total productivity increase by 83.35 million tons, accounting for 3.50% of the overall output. The losses of original farmlands driven by built-up areas invading and occupying arable land are mostly distributed in the regions which have rapid economic development, e.g. Huang-Huai-Hai plain, Yangtze River delta, Zhujiang delta, central part of Gansu, southeast coastal region, southeast of Sichuan Basin and Urumqi-Shihezi. It has led the total productivity to decrease 57.13 million tons, which is 2.40% of the overall output.

Assessing the consequence of land use change on agricultural productivity in China

China's cultivated land has been undergoing dramatic changes along with its rapidly growing economy and population. The impacts of land use transformation on food production at the national scale, however, have been poorly understood due to the lack of detailed spatially explicit agricultural productivity information on cropland change and crop productivity. This study evaluates the effect of the cropland transformation on agricultural productivity by combining the land use data of China for the period of 1990-2000 from TM images and a satellite-based NPP (net primary production) model driven with NOAH/AVHRR data. The cropland area of China has a net increase of 2.79 Mha in the study period, which causes a slightly increased agricultural productivity (6.96 Mt C) at the national level. Although the newly cultivated lands compensated for the loss from urban expansion, but the contribution to production is insignificant because of the low productivity. The decrease in crop production resulting from urban expansion is about twice of that from abandonment of arable lands to forests and grasslands. The productivity of arable lands occupied by urban expansion was 80% higher than that of the newly cultivated lands in the regions with unfavorable natural conditions. Significance of cropland transformation impacts is spatially diverse with the differences in land use change intensity and land productivity across China. The increase in arable land area and yet decline in land quality may reduce the production potential and sustainability of China's agro-ecosystems. (C) 2008 Elsevier B.V. All rights reserved.

黄土高原土壤干层评定指标的改进及分级标准

土壤干层是黄土高原普遍存在的特殊土壤水文现象,研究其现状、成因、防治、调控措施等对科学认识区域植被承载力、土地生产力以及低效林草改造和可持续植被建设等有重要理论与生产指导意义,而合理通用评判指标与分级标准是开展土壤干层研究的基础。目前黄土高原土壤干层尚无统一评判指标与分级标准,给区域土壤干层研究带来困难。本文在已有研究成果的基础上,提出用土壤有效水饱和度/不饱和度作为土壤干层评判指标,并给出其分级标准。该评判指标计算简单,具通用性和可比性,可望成为土壤干层的通用评判指标。

陕北中部丘陵区土壤肥力现状及提高土地生产力的途径

调查分析了延安宝塔区和安塞县 7个乡镇近三年来的粮食生产 ,肥料投入以及各土地类型的土壤肥力状况 ,表明 :投入的化肥中 ,氮肥以低浓度养分的碳铵为主 ,平均占肥料总量的 38.3% ,从施入土壤的 N、P、K养分来看 ,K比例很小 ,结构不合理。土壤肥力总体水平低 ,且不同土地类型差异大 ;由于各乡镇自然和经济状况的差异 ,土地投入量不同 ,从而导致粮食产量相差悬殊 ,并且年际波动大。提高土地生产力的有效途径是培肥土壤和大力推广农作物高产栽培技术

侵蚀条件下坡地土壤水分与有效磷的空间分布特征

坡地的水土流失及磷素在泥沙中的富集不仅导致土地生产力下降、环境恶化 ,也对下游水体的环境造成严重危害。以不同施磷时间的黄绵土为试验材料 ,通过人工模拟降雨试验观察了坡地侵蚀土壤水分含量 (SM)与有效磷含量 (APC)的空间变化特征。结果表明 :自坡顶向下侵蚀土壤表层 0～ 5 cm与 5～ 10 cm的土壤水分 (SM)呈现出完全一致的波浪状递增趋势。有效磷含量 (APC)的空间变化虽然也为波浪状 ,但其节奏要较水分变化快一倍 ,而且 0～ 5 cm与 5～ 10 cm两层间并不同步 ,下层略有滞后。磷向 2 0 cm以下土层的迁移量极少 ,不同坡位间差别不大。施磷 2 4d以前从坡顶向下有效磷含量 (APC)呈降低趋势 ,而施磷 2 4d以后在坡下则略有富集 ;施磷 6 d以前坡地 0～ 5 cm土层有效磷含量 (APC)较 6 d以后低 8%左右

陕北黄土高原农牧交错带土地生产潜力及人口承载力

根据陕北黄土高原农牧交错带生态环境特点以及作物生长发育过程对光、热、水、土资源的要求和利用效率,运用逐步订正法对该地区的土地生产潜力进行了定量估算,并对其土地的人口承载力进行了计算与分析,指出了提高该地区土地生产潜力及人口承载力的途径。结果表明,该地区光温生产潜力为光合生产潜力的65.21%,气候生产潜力为光温生产潜力的37.91%,土壤生产潜力为气候生产潜力的32.19%,现实生产能力仅为土壤生产潜力的42.47%;在现实生产能力水平下,人民生活仅能维持我国低消费水平,如果要实现世界中等消费水平,必须使土地的现实生产能力达到土壤生产潜力的89.40%,气候生产潜力的27.00%。提高该地区土地生产潜力及人口承载力的途径包括提高植被覆盖度,控制土地荒漠化;发展设施农业和灌溉农业,提高作物产量;改进施肥方法,培肥地力;因地制宜,开发滩区等。

The effect of land management on plant community composition, species diversity, and productivity of alpine Kobersia steppe meadow

Grassland degradation is widespread and severe on the Tibet Plateau. To explore management approaches for sustainable development of degraded and restored ecosystems, we studied the effect of land degradation on species composition, species diversity, and vegetation productivity, and examined the relative influence of various rehabilitation practices (two seeding treatments and a non-seeded natural recovery treatment) on community structure and vegetation productivity in early secondary succession. The results showed: (1) All sedge and grass species of the natural steppe meadow had disappeared from the severely degraded land. The above-ground and root biomass of severely degraded land were only 38 and 14.7%, respectively, of those of the control. So, the original ecosystem has been dramatically altered by land degradation on alpine steppe meadow. (2) Seeding measures may promote above-ground biomass, particularly grass biomass, and ground cover. Except for the grasses seeded, however, other grass and sedge species did not occur after seeding treatments in the sixth year of seeding. Establishment of grasses during natural recovery treatment progressed slowly compared with during seeding treatments. Many annual forbs invaded and established during the 6 years of natural recovery. In addition, there was greater diversity after natural recovery treatment than after seeding treatments. (3) The above-ground biomass after seeding treatment and natural recovery treatment were 114 and 55%, respectively, of that of the control. No significant differences in root biomass occurred among the natural recovery and seeded treatments. Root biomass after rehabilitation treatment was 23-31% that of the control.