1、附录 Reclamation of forest soils with excavator tillage and organic amendments Abstract In early 1994, a research project was initiated to evaluate the success of several techniques aimed at restoring productivity to degraded soils on landings near Vama Vama Creek, 44 km east of Prince George in Centr
2、al British Columbia. Soils were developed from morainal parent materials, the usual surface soil texture was silt loam. Two organic amendments were used in this study, including freshly prepared wood chips and old sawdust. An excavator equipped with a site preparation rake was used to till the soils
3、 to a depth of 0.50 m. Organic amendments were subsequently added to the plots, and either left as a mulch or incorporated into the surface 0.20 m of the soil. Nitrogen was applied to all plots at a rate of 225 kg N ha-1, which represents about one-third of the 500700 kg ha-1 that was estimated to b
4、e required to compensate for N immobilization during decomposition of the woody residues. Survival was good for all treatments, but after 3 years, trees were growing best in areas that were treated with tillage alone. Trees growing on areas where old sawdust was used as an amendment had more volume
5、than trees growing in areas where wood chips had been used. Control plots with no treatment had intermediate growth. Soil temperature and chemical properties were evaluated for their effect on growth.#2000 Elsevier Science B.V. All rights reserved. Keywords: Forest soil rehabilitation； British Colum
6、bia； Soil disturbance； Soil conservation； Soil productivity； Landing and road rehabilitation 1. Introduction Soils on forest landings in central British Columbia are frequently characterized by compaction and nutrient depletion (Carr, 1988a). Degraded soils on landings and other areas where soils ha
7、ve been disturbed by forest operations often support only meager growth of planted conifers (Arnott et al., 1988). In many cases, soil conditions are so degraded that planting is not attempted on landings. Restoring soil productivity on degraded soils requires that growth-limiting conditions be alle
8、viated (Bulmer, 1998). Tillage is frequently employed to decompact soils and improve soil productivity(Andrus and Froehlich, 1983). On coarse-textured soils, tillage alone may provide significant benefits for growth of conifers such as lodgepole pine, although the long-term consequences of soil nutr
9、ient depletion may be of concern. On fine-textured soils,tillage results have been inconsistent (Carr, 1988b；McNabb, 1994), partly because there is a narrow rangeof moisture content where effective tillage can be carried out, but also because stable aggregates are required to prevent puddling and po
10、or physical conditions from reappearing shortly after tillage. Stable soil aggregates form when soil mineral grains establish an intimate association with soil organic matter(Tisdall and Oades, 1982). Several approaches could be employed to re-establish stable soil structure after tillage of fine-te
11、xtured soils. A cover crop of deep rooted grasses and legumes could be established to provide organic matter and enhance biological activity in the root zone,thereby encouraging the development of stable soil aggregates. Another approach that has been proposed involves the incorporation of organic a
12、mendments into the surface soil layer to bring organic and mineral soil materials in contact with each other, and possibly encourage the formation of stable aggregates. This project was developed in order to gain more information about methods for restoring productivity to compact and nutrient-poor
13、soils. We evaluated the effect of several combinations of tillage and the addition of organic amendments on soil properties and the establishment and early growth of lodgepole Pine. 2. Materials and methods 2.1. Study sites The study was carried out on three forest landings 44 km east of Prince Geor
14、ge, in the SBSwk1 biogeoclimatic subzone. Soils were developed from morainal parent materials. The usual surface soil texture was silt loam, but in at least one location, a clay-rich B horizon was encountered. Coarse fragment content varied between 15 and 40%. The landings were located on level or g
15、ently sloping areas. Prior to treatment, there was little vegetation growth on the Landings. 2.2. Experimental design Nine treatments were applied to 5 m 6 m plots, as described in Table 1. Two control plots were established on each landing. The two organic amendments used were wood chips produced a
16、s part of treatments to reduce re hazard on the adjacent cutblock, and well-rotted sawdust from an old sawmill site. These materials are typical of soil amendments that may be available at remote rehabilitation sites. The chips had typical particle size of 0.1 m 0.05 m 0.005 m,while the sawdust part
17、icles had all dimensions smaller than 0.003 m. 2.3. Treatments Treatments were carried out in the summer of 1994 using an excavator equipped with a five-tooth site preparation rake. Soils were tilled to a depth of 0.50 m, and organic amendments were subsequently shoveled onto the plots to obtain an
18、even distribution of the material. Amendments were either left as a mulch or subsequently incorporated into the surface 0.20 m of the soil. Pine seedlings (PSB 313) were planted at 1 m spacing on all plots. A legume seed mix was applied in the summer of 1995, but very poor establishment of the legum
19、e cover crop occurred due to dry weather.Grass and legume cover has been maintained at a low level throughout the experiment. All plots, including controls, were fertilized in the summer of 1995, using a combination of urea (45-0-0) and a complete NPK fertilizer (18-18-18). Nitrogen was applied at a
20、 rate of 225 kg N ha-1, which represents about one-third of the 500700 kg N ha-1 that was estimated to be required to compensate for N immobilization during decomposition of the woody residues. The plots received 50 kg ha-1 of K2O and P2O5. 2.4. Soil analysis and tree productivity measurements Compo
21、site soil samples were collected in October,1994 from the recently treated plots. Samples were air dried, passed through a 0.002 m sieve, and analyzed at the Pacific Forestry Centre. Soil temperature and moisture were evaluated approximately every two weeks during the summer of 1995 by obtaining thr
22、ee readings with a hand-held thermometer that was inserted 0.15 m below the mineral soil surface. Tree survival and early growth was monitored after one,two, and three growing seasons. Tree height and caliper was determined, along with an assessment of the tree condition. Tree volume was determined
23、as the volume of a cylinder with base diameter equal to the caliper, and height equal to the seedling height. 3. Results and discussion 3.1. Soil properties Soil temperature results are presented in Fig. 1.Even though no analysis was done on the data, and replication was limited, general conclusions
24、 appear to be justified. Daytime soil temperatures tended to be lower for mulch treatments compared to soils without added amendments. Plots where organic amendments had been tilled into the surface had intermediate soil Temperatures. The sawdust had a much lower C : N ratio than the wood chips (Fig
25、. 2), reflecting higher N concentrations for woody materials that have experienced several years of decomposition. P, Ca, Mg and Fe concentrations also appeared to be slightly higher in the sawdust material (data not shown). Concentrations of other elements did not appear to vary consistently between the sawdust and wood chip amendments.
