Seasonal changes of understorey herbage yield in relation to light intensity and soil moisture content in a Pinus pinaster plantation

The relationship of understorey herbage yield with light intensity and soil moisture content was investigated in a 20-year-old Pinus pinaster plantation in Kilkis of Macedonia, northern Greece, in three seasons (fall, winter and spring). The plantation was thinned at three density levels, high, medium and low (2500, 1750 and 1000 trees/ha respectively) and it was seeded with Dactylis glomerata. In addition, two fertilization levels (0 and 110 N+150 P₂O₅ kg/ha) and grazing intensity levels (0 and 0.8 sheep/ha/yr) were applied in a split-split plot experimental design. It was found that herbage yield was highest in the ungrazed and fertilized low tree density stands in all seasons. In the medium tree density stand, although light was lacking, fertilized plots produced higher herbage yield as compared to unfertilized low tree density stands while fertilization is of no use in close stands if herbage production is the goal. Animals seemed to prefer fertilized and medium density stands. Third degree polynomial equations were the best to explain herbage variation through the seasons both in fertilized and unfertilized plots.     

Establishment of Prosopis cineraria (L.) druce in the hot deserts of India

Prosopis cineraria (L.) Druce, commonly known as Jandi, is a deep rooted, nitrogen fixing, multipurpose tree endemic to the hot deserts of India. These trees are the essential component of the agroforestry land use system in these parts of India. The shade-intolerant tree reproduces poorly in nature and is difficult to propagate vegetatively. Germination up to 86.6% was observed after 15 days in seeds soaked in water at room temperature for 72 h. In another treatment, pouring of boiling water twice (at 0 and 6 h) over seeds and germinating after 12 h produced germination rates of 92.6%. Field establishment of containerized transplants in polythene bags (22×10 cm; 150 gauge) gave 90.3% survival after 6 months and 75.4% survival after 24 months. Seedlings were irrigated once during transplanting with 15 1 water. Bare root transplants and manual direct seeding after 6 months had a survival of 30.8 and 45.0%, respectively. Increased levels of nutrients (N, P and K), moisture content and organic carbon were observed under plantations as compared to open areas.     

Seasonal pattern of nitrogen mineralization and soil moisture beneath Faidherbia albida (synAcacia albida) in central malawi

On fertile alluvial soils on the lakeshore plain of Malawi, maize (Zea mays L.) yields beneath canopies of large Faidherbia albida (synAcacia albida) trees greatly exceed those found beyound tree canopies, yet there is little difference in soil nutrients or organic matter. To investigate the possibility that soil nutrient dynamics contribute to increased maize yields, this study focused on the impact of Faidherbia albida on nitrogen mineralization and soil moisture from the time of crop planting until harvest. Both large and small trees were studied to consider whether tree effects change as trees mature.During the first month of the rainy season, a seven-fold difference in net N mineralization was recorded beneath large tree canopies compared to rates measured in open sites. The initial pulse beneath the trees was 60 g N g^–1 in the top 15 cm of soil. During the rest of the cropping cycle, N availability was 1.5 to 3 times higher beneath tree canopies than in open sites. The total production of N for the 4-month study period was 112 g N g^–1 below tree canopies compared to 42 g N g^–1 beyond the canopies. Soil moisture in the 0–15 cm soil layer was higher under the influence of the tree canopies. The canopy versus open site difference grew from 4% at the beginning of the season to 50% at the end of the cropping season.Both N mineralization and soil moisture were decreased below young trees. Hence, the impact of F. albida on these soil properties changes with tree age and size. While maize yields were not depressed beneath young F. albida, it is important to realize that the full benefits of this traditional agroforestry system may require decades to develop.     

安徽淮河堤防杨树防护林生长与土壤养分的关系

对安徽淮河堤防Ⅰ-69杨防护林生长与土壤养分关系进行了调查分析,结果表明,不同立地条件下杨树防护林生长差异显著,10~12年生林分年平均蓄积生长量为10.45~23.27 m3.hm-2.a-1,林分生产力水平的高低主要受控于土壤有机质含量及氮、磷有效性。     

庞泉沟自然保护区河岸林群落的土壤种子库特征

以人工拣种结合种子萌发法研究了庞泉沟自然保护区9种河岸林群落的土壤种子库特征,结果表明: 9种群落的土壤种子库密度间于684±108 - 2 696±266粒·m-2,69.27% - 88.65%的种子留存于0 - 5 cm的层次,沙棘灌丛的种子库密度最大,乌柳灌丛最小;离河岸10 m和20 m处的种子库密度大于岸边、离河岸30 m和40 m处;种子库包含的40种植物以多年生草本为主,灌木和草本种多为耐干扰种,存在典型的湿地植物,但种子储量以先锋种白桦最丰;辽东栎无完整种子,白桦、华北落叶松、云杉和油松的种子活力保持期为1 - 2年,多数草本的种子活力保持期超过2年;按照群落土壤种子库的相似性,将群落划分为林分开始期、林分排除期、下层再现期和老熟期4个演替阶段。演替后期群落的种子库密度、丰度以及与地上植被的相似性都小于前期群落。土壤种子库是森林自然更新及种群恢复的重要基础,本文对于研究地区河岸林的保护和重建具有重要的理论意义。     

水分和温度对挪威云杉林枯枝落叶层浸提液pH值的影响

在室内控制条件下研究含水量和温度对富含ＮＨ＾＋４的严重酸化挪威云杉林枯枝落叶层物质饱和是液ＰＨ值的影响,包括未分解层ＯＬ,半分解层ＯＦ和已分解层ＯＨ,在为期１ａ的实验期间内没有元素的输入,淋失和根系吸收,但可相对自由地进行气体交换。     

施用磷肥对杉木幼林土壤养分和磷组分的影响

杉木［Ｃｕｎｎｉｎｇｈａｍｉａｌａｎｃｅｏｌａｔａ（Ｌａｍｂ．）Ｈｏｏｋ．］人工林土壤立地大多供Ｐ不足,杉木幼林施用磷肥肥效显著。李贻铨等认为施Ｐ、Ｋ肥能促进杉木幼林生长［１,２］;叶仲节认为幼林施Ｐ肥初期有效,施Ｎ无效,施Ｋ还会出现负效应［３］。作...     

A Study on Water Exchange in Root Zone of ProtectiveForest Ecosystem in Loess Area

ＡＳｔｕｄｙｏｎＷａｔｅｒＥｘｃｈａｎｇｅｉｎＲｏｏｔＺｏｎｅｏｆＰｒｏｔｅｃｔｉｖｅＦｏｒｅｓｔＥｃｏｓｙｓｔｅｍｉｎＬｏｅｓｓＡｒｅａＹｕＸｉｎｘｉａｏＣｏｌｌｅｇｅｏｆＳｏｉｌａｎｄＷａｔｅｒＣｏｎｓｅｒｒａｔｉｏｎ，ＢｅｉｊｉｎｇＦｏｒｅｓｔ...     

砂质土肥力状况及其与毛白杨生长关系的研究

对黄河故道冲积砂质上的肥力状况和毛白杨生长因子之间的关系进行了研究，着重分析了土壤养分和水分在土体中的分布规律，及其与土壤质地的关系，以及不同生长季节毛白杨的叶片营养特征和树高、胸径生长量与砂质土水分、养分含量的相关性。结果表明：砂质土肥力低下；土壤质地、养分和水分变化状况与树木生长关系密切，尤其是土壤粘粒、水分和氮素含量与毛白杨生长呈明显的正和关。故可通过施肥、灌水、改善土壤保水保肥特性来调整和控制林木生长。