Site preparation: Water relations and growth of newly planted jack pine and white spruce

Bareroot jack pine (Pinus banksiana Lamb.) and white spruce (Picea glauca (Moench) Voss) were planted near Elliot Lake, Ontario, on a boreal reforestation site. Site preparation treatments were mixed, mineral and undisturbed (i.e., control) soil. Seedling water relations and growth were examined during the first field season. During the first 28 days after planting, jack pine base (i.e., predawn) and minimum xylem water potential readings were more negative in the control site preparation treatment. White spruce, during the first 10 days, in all site preparation treatments had base and minimum xylem water potential readings more negative than –1.7 MPa. By day 28 base xylem water potentials of white spruce had increased to approximately –1.0 MPa in all site preparation treatments. As the growing season progressed, white spruce minimum xylem water potential readings ceased exceeding the measured turgor loss point first in the mixed followed by the mineral and then control site preparation treatment. Jack pine minimum xylem water potential readings, in all site preparation treatments, almost never exceeded the measured turgor loss point. Water stress and stomatal optimization integrals, day 28 and 125, for both species showed least water stress and greater stomatal optimization in the mixed, mineral and control site preparation treatments, respectively. Both species had less new root growth in the field during the first 28 days after planting compared to seedlings grown for 28 days in a greenhouse for root growth capacity testing. Root growth at 28 days and both shoot and root development at the end of the growing season, were greatest to least in mixed, mineral, and control site preparation treatments, respectively.     

Agroforestry research and development in southern Africa during the 1990s: Review and challenges ahead

In light of the large number of empirical studies of agroforestry adoption published during the last decade, we believe it is time to take stock and identify general determinants of agroforestry adoption. In reviewing 120 articles on adoption of agricultural and forestry technology by small holders, we find five categories of factors that explain technology adoption within an economic framework: preferences, resource endowments, market incentives, biophysical factors, and risk and uncertainty. By selecting only empirical analyses that focus on agroforestry and related investments, we narrow our list down to 32 studies primarily from tropical areas. We apply vote-counting based meta-analysis to these studies and evaluate the inclusion and significance of the five adoption factors. Our analysis shows that preferences and resource endowments are the factors most often included in studies. However, adoption behavior is most likely to be significantly influenced by risk, biophysical, and resource factors. In our conclusion, we discuss specific recommendations for the next generation of adoption studies and meta-analyses that include considering a fuller menu of variables, reporting key statistics and marginal probabilities, and conducting weighted meta-regressions.This revised version was published online in November 2005 with corrections to the Cover Date.     

高温水供热干燥速生杉木方材

运用高温水供热系统干燥速生杉木方材。生产性试验表明，6天内初含水率为55．5％的杉木方材干至始含水率5．4％，干燥质量符合细木工板生产的要求（少数高含水率木材除外）。此干燥法集中供热，具有热效率高、运行安全和经济可行等特点。     

Vesicular-arbuscular mycorrhiza effects on Gliricidia sepium and Senna siamea in a fallowed alley cropping system

Nitrogen fixing and non-N₂ fixing legumes such as Gliricidia speium and Senna siamea have been used in alley cropping systems for soil improvement and source of N for food crops. However their establishments could be limited by P and moisture deficiencies in degraded soils. Vesicular-arbuscular mycorrhizal fungi can help to overcome these deficiencies. We examined the effects of a vesicular-arbuscular mycorrhizal (VAM) fungus, Glomus deserticola, on the performance of sole hedgerow trees of Gliricidia sepium and Senna siamea and their mixtures (interplanted) in a fallowed alley cropping experiment on a degraded Alfisol in southwestern Nigeria. Percentage root infection by VAM fungi was higher in inoculated plants than in uninoculated ones irrespective of whether they were interplanted or non-interplanted. Inoculation with G. deserticola increased dry matter accumulation and nutrient uptake (N. P, Mg and K) but there was no significant interaction between mycorrhizal inoculation and interplanting for growth and nutrient uptake except for the uptake of P, Mg and K in G. sepium. Inoculation with G. deserticola reduced leaf shedding of G. sepium by 50% but did not have the same effect for S. siamea. For both tree species inoculated plants extracted more water from 0–30 cm depth than the uninoculated ones.     

Agroforestry systems and soil surface management of a tropical alfisol:

Field runoff plots, 70 x 10 m each, were established on a tropical Alifisol in southwestern Nigeria to monitor water runoff, soil erosion and nutrient loss in water runoff. The non-agroforestry control treatment (A) was established at two levels: plow-till and no-till systems of seedbed preparation. There were two agroforestry systems based on contour hedgerows of (B) Leucaena leucocephala and (C) Gliricidia sepium established at 4-m and 2-m spacings. Field plots were established in 1982 and hydrological measurements were made for uniform maize-cowpea rotation for 12 consecutive growing seasons from 1982 through 1987. Once established hedgerows of Leucaena at 2-m spacing were extremely effective in reducing water runoff and controlling erosion. Runoff, erosion and nutrient losses were generally more from maize grown in the first season than from cowpea grown in the second. Mean seasonal erosion from maize was 4.3, 0.10, 0.57, 0.10, 0.64 and 0.60 t/ha for plow-till, no-till, Leucaena-4m, Leucaena-2m, Gliricidia-2m treatments, respectively. Mean runoff in the first season from treatments listed in the order above was 17.0, 1.3, 4.9, 3.3, 4.3, and 2.4 percent of the rainfall received. There were high losses of Ca and K in water runoff from the plow-till treatment. In contrast to runoff and erosion, losses of bases in water runoff from agroforestry treatments were relatively high, high concentration of bases in runoff was probably due to nutrient recycling by the deep-rooted perennials.     

Process studies in aPinus radiata-pasture agroforestry system in a subhumid temperature environment. I. Water use and light interception in the third year

In this study we determined soil moisture storage, evapotranspiration (ET) and light interception in an agroforestry trial consisting of pine trees grown over (1) control (bare ground), (2) ryegrass/clovers (Lolium perene/Trifolium spp.), (3) lucerne (Medicago sativa), and (4) ryegrass only during the third growing season between 1992 and 1993. The results show that:

水分胁迫对栓皮栎幼苗生理特性及生长的影响

通过盆栽实验，研究了在不同的水分条件下栓皮栎幼苗生理特性的变化和苗木生长量的变化。研究表明，在水分胁迫初期，随土壤含水量的降低，栓皮栎叶片的净光合速率、蒸腾速率下降，而水分利用效率提高。在水分胁迫末期，由于长期的干旱胁迫，水分条件最差的一组苗木已干枯死亡，土壤含水量从38．123％下降到20．323％时，净光合速率和蒸腾速率均下降，水分利用效率也下降。随着土壤含水量的降低，苗高、地径和生物量均有下降的趋势，其中生物量下降的幅度最大。     

2006年特大干旱条件下森林植被对土壤水分的影响

2006年四川发生了百年一遇的特大干旱。于旱期结束末,调查了蓬安县境内两座丘陵-石马寨(栎柏混交林)和碉堡梁(人工柏木林)上、中、下坡林地和林带中耕地及坡脚农田的土壤含水量;调查了四川盆地丘陵区内5个县9个乡镇17个小流域有无农田防护林条件下,稻田开裂起始时间和裂缝宽;以及按照自然地理条件相近、森林覆盖率有较大差异的原则,调查了宣汉县和达县5对乡镇(森林覆盖率高的乡镇森林覆盖率为28.26%～46.85%,平均为37.24%,相对应的低的乡镇森林覆盖率为12.75%～26.74%,平均为18.64%)内不同台地的土壤含水量。结果表明,混交林林地的保水能力强于纯林林地,林地的保水能力强于耕地,农田防护林对水稻具有庇护作用,森林覆盖率高的地区土壤保水能力强于森林覆盖率低的地区土壤。在干旱期末坡上、中、下部位的0～40 cm土层中,栎柏混交林林地的含水量比柏木纯林林地高出3%～7%,林地的土壤含水量比林带中的耕地高出0.7%～2.1%;栎柏混交林带中的耕地含水量比柏木纯林带中的耕地高出3%～6%,石马寨的坡脚农田含水量比碉堡梁的高出5%;在干旱期末不同台地0～40 cm土层中,与森林覆盖率低的地区相比,森林覆盖率高的地区水稻田含水量高3%～7%,二台土高4%～8%,三台土高2%～8%;有农田防护林的农田土壤开裂时间比无农田防护林的推迟5 d～20 d,裂口宽平均窄0.1 cm～3.1 cm。     

Leaf-water potential and soil-water depletion of walnut mulched with polyethylene and intercropped with alfalfa in Central Italy

In Italy, new agroforestry cultural models could play an important role in the diffusion of plantation forestry timber species. We studied the stem growth rates and leaf water potentials () of common walnut (Juglans regia L.), and gravimetric soil moisture (_DW) depletion during the third and fourth growing seasons in an agroforestry trial in central Italy. Since the establishment of experimental plots in 1992, walnut was intercropped with alfalfa (Medicago sativa L.), with or without polyethylene (PE) mulching along tree rows. By the end of the study period, the unmulched-intercropped walnut was almost 68% smaller in stem diameter and height than the sole-unmulched control, demonstrating walnuts sensitivity to alfalfa competition. The competitive effect of alfalfa on walnut stem growth was effectively controlled/reduced by PE mulching. Stem growth rates of mulched-intercropped walnut were always lower than the control, but much higher (ca. 235% in stem diameter and height) than those of unmulched-intercropped walnut. The higher field performance of mulched-intercropped walnut compared to the un- mulched-intercropped treatment was associated with higher soil moisture and predawn and midday values during the summers driest periods. The presence of PE mulching was also associated with lower levels of soil moisture during the early and late growing season, but this did not negatively affect walnut and growth rates. These results suggest that in the climatic conditions of central Italy, competition for soil moisture between young common walnut trees and alfalfa can be substantially lowered, but not completely eliminated, by PE mulching.This revised version was published online in November 2005 with corrections to the Cover Date.     

稻壳灰同时制备脱色剂和水玻璃的研究

基于稻壳灰（RHA）含有均匀分布的主要由SiO2组成的高含量矿物质的事实，研究了RHA综合利用的方法。RHA先经碱法处理后转化为水玻璃和脱硅RHA（DRHA），然后DRHA用硫酸活化制得应用于植物油精炼中的脱色剂纯RHA（PRHA）。分别探讨了影响水玻璃模数和PRHA脱色能力的因素。结果表明，在2-3mol／L范围内改变NaOH浓度或在2-3h范围内改变溶煮时间，可获得2．3～3．6模数的水玻璃产品。高脱硅率有利于PRHA的多孔性形成。在NaOH溶液浓度2mol／L和溶煮时间2h条件下，RHA转化为模数3．3的水玻璃和DRHA，SiO2溶出率达到94.83％。活化DRHA制备PRHA的最佳工艺为：硫酸质量分数5％、活化时间4h、活化温度90℃。PRHA对中性大豆毛油的脱色能力是目前植物油工业中常用的活性凹凸棒石粘土的3倍。