基于HVI测试的标准化操作规范

为了规范大容量棉花测试仪的使用、校准及维护,提高检测结果准确性.作者根据HVI应用手册和实际操作经验,总结了大容量棉花测试仪的标准化工作各项要求.主要包括样品管理、气电及空间要求、恒温室、标准化仪器、校准与核查、比对试验、测试人员、健康安全、消防安全等.供业内同仁参考.     

景谷县森林蓄积量遥感估测及其动态变化分析

以云南省景谷县为研究区,基于Landsat5和Landsat8遥感数据,利用2012年和2017年两期全国森林资源连续清查实地调查数据,建立多元逐步回归和随机森林模型对景谷县森林蓄积量进行遥感估测对比研究.结果显示:综合建模精度来看,随机森林法在相同样地数量条件下具有更好的估测效果;从估测结果与林地保护利用规划和林地变...     

人工降雨条件下不同坡度红壤坡面迳流泥沙变化特征研究

在人工模拟降雨强度为1.44 mm/min的条件下,研究了不同坡度(β)红壤近似裸地坡面迳流、泥沙的变化特征,研究结果表明:①地表迳流量随坡度的增大而迅速增加。②当β≤23°时,土壤侵蚀量随坡度的增大而迅速增加;当25°≤β≤40°时,土壤侵蚀量随坡度变化较小。③坡面土壤侵蚀的临界坡度则介于23°~25°之间。④坡度与侵蚀量关系可用函数表示为:S=199.1×L1.65×tan1.4β(0°≤β≤23°)。     

补灌量和覆盖量变化对旱地春小麦叶面积指数的影响

免耕覆盖中补灌量和秸秆覆盖量变化对叶片生长有较大影响,以甘肃省定西市安定区1979—2019年历史气象数据为基础,运用APSIM模型对补灌量与覆盖量耦合变化时旱地春小麦的叶面积指数进行模拟,并采用方差分析、二次多项式回归、单因素分析等方法,研究补灌量和覆盖量对旱地春小麦叶面积的影响机制。结果表明：在试验设计范围内,旱地春小麦叶面积指数随着补灌量变化在分蘖—拔节期呈开口向下的二次抛物线先增后减变化,补灌量在252.09 mm时春小麦叶面积指数出现最大值为1.83,其他各个时期均呈开口向上的二次抛物线递增变化。随着秸秆覆盖量变化,叶面积指数在出苗—分蘖期,呈开口向下的二次抛物线先增后减变化,试验设计范围内秸秆覆盖量为2397.09 kg/hm²时春小麦叶面积指数出现最大值为0.59,分蘖—拔节期呈开口向下的二次抛物线递增变化;其他各个时期均呈开口向上的二次抛物线递增变化。相同阶段下,补灌量每增加50 mm,春小麦叶面积指数最大增幅13.95%;秸秆覆盖量每增加1000 kg/hm²,春小麦叶面积指数最大增幅3.7%。补灌量对春小麦叶面积指数的影响...     

黄牛木种群空间分布格局研究

为促进黄牛木Cratoxylum cochinchinense在珠三角地区生态建设中的推广和应用,采用样方调查法,于2016-2017年在广州市和台山市3个黄牛木天然林集中分布区布设样地,通过绘制种群空间分布点位置图,结合方差均值比率法和聚集度指标,分析种群的空间分布类型、聚集程度,从而揭示黄牛木种群的空间分布特性、生...     

2003—2018年中国森林火灾时空分布格局研究

基于2003—2018年的中国森林火灾统计数据,全面分析了森林火灾发生的时空分布格局,定量分析了其统计学规律,旨在为森林火灾预测、管理和风险决策提供基础支撑.分析结果表明,森林火灾的发生具有极强的随机性和离散性,通过森林火灾总次数、火场面积和受害森林面积的平均数来反映森林火灾发生风险将会导致评估结果偏高.森林火灾发生次...     

Improving wood volume predictions in dry tropical forest in the semi-arid Brazil

The volumetric variability of dry tropical forests in Brazil and the scarcity of studies on the subject show the need for the development of techniques that make it possible to obtain adequate and accurate wood volume estimates. In this study, we analyzed a database of thinning trees from a forest management plan in the Contendas de Sincorá National Forest, southwestern Bahia State, Brazil. The data set included a total of 300 trees with a trunk diameter ranging from 5 to 52 cm. Adjustments, validation and statistical selection of four volumetric models were performed. Due to the difference in height values for the same diameter and the low correlation between both variables, we do not suggest models which only use the diameter at breast height (DBH) variable as a predictor because they accommodate the largest estimation errors. In comparing the best single entry model (Hohenald-Krenn) with the Spurr model (best fit model), it is noted that the exclusion of height as a predictor causes the values of 136.44 and 0.93 for Akaike information criterion (AIC) and adjusted determination coefficient (R2 adj), which are poorer than the second best model (Schumacher-Hall). Regarding the minimum sample size, errors in estimation (root mean square error (RMSE) and bias) of the best model decrease as the sample size increases, especially when a larger number of trees with DBH≥15.0 cm are randomly sampled. Stratified sampling by diameter class produces smaller volume prediction errors than random sampling, especially when considering all trees. In summary, the Spurr and Schumacher-Hall models perform better. These models suggest that the total variance explained in the estimates is not less than 95%, producing reliable forecasts of the total volume with shell. Our estimates indicate that the bias around the average is not greater than 7%. Our results support the decision to use regression methods to build models and estimate their parameters, seeking stratification strategies in diameter classes for the sample trees. Volume estimates with valid confidence intervals can be obtained using the Spurr model for the studied dry forest. Stratified sampling of the data set for model adjustment and selection is necessary, since we find significant results with mean error square root values and bias of up to 70% of the total database.     

Cultivation effects on soil texture and fertility in an arid desert region of northwestern China

In arid desert regions of northwestern China, reclamation and subsequent irrigated cultivation have become effective ways to prevent desertification, expand arable croplands, and develop sustainable agricultural production. Improvement in soil texture and fertility is crucial to high soil quality and stable crop yield. However, knowledge on the long-term effects of the conversion of desert lands into arable croplands is very limited. To address this problem, we conducted this study in an arid desert region of northwestern China to understand the changes in soil physical-chemical properties after 0, 2, 5, 10, 17, and 24 years of cultivation. Our results showed that silt and clay contents at the 17-year-old sites increased 17.5 and 152.3 folds, respectively, compared with that at the 0-year-old sites. The soil aggregate size fraction and its stability exhibited an exponential growth trend with increasing cultivation ages, but no significant change was found for the proportion of soil macroaggregates (>5.00 mm) during the 17 years of cultivation. The soil organic carbon (SOC) content at the 24-year-old sites was 6.86 g/kg and increased 8.8 folds compared with that at the 0-year-old sites. The total (or available) nitrogen, phosphorus, and potassium contents showed significant increasing trends and reached higher values after 17 (or 24) years of cultivation. Changes in soil physical-chemical properties successively experienced slow, rapid, and stable development stages, but some key properties (such as soil aggregate stability and SOC) were still too low to meet the sustainable agricultural production. The results of this long-term study indicated that reasonable agricultural management, such as expanding no-tillage land area, returning straw to the fields, applying organic fertilizer, reducing chemical fertilizer application, and carrying out soil testing for formula fertilization, is urgently needed in arid desert regions.     

短轮伐期桉树人工林个体林木特征研究

利用广东高要和广西扶绥两地14个2~10年生桉树林分样地共287株样木,研究短轮伐期桉树人工林个体林木特征指标,并比较现有广西良种桉二元带皮和去皮材积公式估算个体林木材积的准确性,分析不同年龄、林分和径阶林木的出材率。结果表明:带皮和去皮林木的胸高形数为0.504±0.004 2和0.529±0.004 4、实验形数为0.410±0.002 4和0.427±0.002 7、形率为0.657±0.003 4和0.690±0.003 6、高径比为1.22±0.017和1.43±0.019。用广西良种桉二元带皮和去皮材积公式估算单株林木带皮和去皮材积与实际材积高度相关(r>0.99),但估算值普遍偏低,平均分别小3.7%和21.0%;尤以用带皮材积公式估算去皮材积比用去皮材积公式估计要准确,平均只小2.3%。如以6年生以上样地和尾径4 cm以上的去皮林木为实际出材,5个相关样地林分平均出材率为(73.3±4.31)%,最小为54.6%,最大为81.5%。     

车-液耦合响应下液罐车稳定性控制仿真

为了提高液罐车行驶安全性、减少液罐车侧翻、失稳所带来的危害,对于液罐车在转向或换道时车-液耦合动态响应对整车稳定性的影响进行了研究。联合液体纳维斯托克斯和流动控制方程,应用计算流体动力学软件ANSYS/Fluent建立并求解液体晃动模型,通过结合液体晃动模型和三自由度液罐车刚体模型获得液罐车车-液耦合动力学模型,分析有无控制策略情况下,液体晃动对液罐车横向稳定性的影响。仿真结果表明:提出的模糊差动制动控制策略能够有效提高车辆抗侧翻能力,减少罐车运输过程中交通事故的发生,对液罐车运输有指导意义。