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911.
To optimize biomass and crude protein (CP) production for leucaena (Leucaena leucocephala) in southern Texas, field trials
were conducted with treatment combinations of three levels of phosphorus (P) , two levels of Mg and two levels of soluble
trace element mixture (STEM). The P was banded in the soil while the Mg and micronutrient blend were applied to the foliage.
A combination of P (22 kg ha-1), Mg and STEM fertilizers significantly increased biomass from 2555 kg ha-1 to 3028 kg ha-1. This treatment was associated with an increase in leaf CP from 27.9% to 31.0%. P fertilizer had no significant effect on
leaf P, but significantly increased leaf nitrogen (N) and leaf copper (Cu). A foliar spray of Mg significantly increased leaf
N, P, and Cu. A foliar spray of a complete micronutrient blend increased leaf Cu. Biomass production was correlated positively
(decreasing order) with leaf Cu, N, and Mg and negatively with Zn. Leaf N was positively correlated with leaf P and calcium.
The critical tissue concentrations (CTC) (where 90% of predicted maximum leaf protein was obtained) were 0.18% and 4.49 mg
kg-1 for leaf P and Cu, respectively.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
912.
C. Rhoades 《Agroforestry Systems》1995,29(2):133-145
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. 相似文献
913.
Indices of soil nitrogen availability for an ecological site classification of British forests 总被引:1,自引:0,他引:1
S.McG. Wilson D.G. Pyatt D. Ray D.C. Malcolm T. Connolly 《Forest Ecology and Management》2005,220(1-3):51-65
An adequate supply of nitrogen (N) is essential for the successful establishment and sustainable productivity of forest stands. N deficits may necessitate the use of artificial fertilisers. Availability of N in the inorganic forms, and the relative abundance of the NO3-N and NH4-N components, influences the species composition of natural forest vegetation. Hence it is essential to use reliable measures of soil N supply that fully reflect its ecological significance. The new Ecological Site Classification (ESC) used in British forestry employs a multi-factorial definition of soil nutrient regime (SNR), including soil N. To develop this, a soil and vegetation study was made at 89 forest sites throughout Great Britain covering the major soil types used for forestry. “Total N” levels were compared with separate pre- and post-incubation measures of the two inorganic N components as potential indices of soil N supply. Multivariate statistical analysis showed that the major discriminant chemical variables for the sampled soils were pH, calcium and NO3-N and that these were also the main variables influencing the species composition of the ground vegetation. Total N and NH4-N were less effective discriminant variables for these sites. In some infertile soils the levels of NH4-N or total N may be of greater importance, as NO3-N is usually in very limited supply. A multivariate gradient of SNR, which incorporates the NO3-N measures, has been adopted for use within the ESC system. The position of a site on this gradient can be estimated quantitatively from soil type, ground vegetation species composition and humus type. This enables soil N supply and overall SNR to be assessed in a simple but effective way that guides the operational management of British forest soils for sustainable productivity. It will also be possible to use these techniques to monitor the nutritional status of forest sites over time. 相似文献
914.
To determine if inoculation increases nodulation and yield of bare-root red alder (Alnus rubra Bong.), fumigated nursery plots were treated with inoculum and ammonium sulfate (28 kg N ha–1) in a factorial experiment. Inoculum was alder soil with 100 infective units of Frankia g–1. Seedlings were evaluated for nodulation at age 10 wk and when lifted, at age 9 mo. Inoculation produced earlier and more extensive nodulation and increased seedling root collar diameter, height, and dry weight. Fertilization decreased seedling height, but did not decrease nodulation. No interaction of fertilization with inoculation was found. Inoculated unfertilized plots had the highest yield of packable seedlings (257 m–2), and uninoculated fertilized seedlings had the lowest yield (126 m–2). 相似文献
915.
本研究通过采用氮的K边X光吸收近边结构(XANES)技术来了解森林土壤有机氮,以此深入研究土壤中有机氮种类与其转化的定量关系。土壤样品采自台湾中部的云杉、铁杉林与草地。结果表明,氮的 XANES 可以揭示样品中不同的氮的种类。在土壤腐植质、可溶性氮及本体土壤中胺态及吡咯氮占了主要的比率。然而不同处理及植被下的土壤样品氮的种类分布是不同的。云杉与铁杉土壤可溶性有机氮在402.3 eV 能量处有显著的差异。在A层土壤中,吡啶类氮含量要显著高于O层土壤,说明氮在不同土层中的转化率存在极大的差异,这种变化对于氮在森林土壤中的循环将起重要作用。图3表1参8。 相似文献
916.
917.
918.
Vendrame Wagner A. Holliday Christopher P. Montello Paul M. Smith Dale R. Merkle Scott A. 《New Forests》2001,21(3):283-292
Cryopreservation has become anessential tool for operational application offorest tree embryogenic cultures, due to thelong evaluation periods needed for treesregenerated from these cultures. Fiveyellow-poplar (Liriodendron tulipifera)and seven sweetgum (Liquidambar spp.)embryogenic culture lines werestored in liquid nitrogen for 48 hours, afterwhich they were thawed and tested for regrowthand ability to produce somatic seedlings.Combinations of two sorbitol pretreatments andthree dimethylsulfoxide (DMSO) cryoprotectantlevels were evaluated for their impact onrecovery following cryogenic storage. The bestresults were obtained with 0.4 M sorbitol and5% DMSO, which provided 100% recovery.Somatic seedlings were regenerated from allculture lines and treatments, except for atransgenic sweetgum line. 相似文献
919.
Water is usally thought of a limiting factor for the restoration of semi-arid ecosystem. In the growing season of 2006, a study was conducted to determine the effects of modeling precipitation on seasonal patterns in concentrations of soil-available nitrogen and to describe the seasonal patterns in soil nitrogen availability and seasonal variation in the rates of net nitrogen mineralization of topsoil at Daqinggou ecological station in Keerqin sand lands, Inner Mongolia Autonomous Region, China. Manipulation of water (80 mm) was designed to be added to experiment plots of sandy grasslands in dry season. Water addition (W) treatment and control (CK) treatment were separately taken in six replications and randomly assigned in 12 plots (4 m×4 m for each) with 2-m buffers betweens. Results showed that the content of soil inorganic nitrogen and net nitrogen mineralization rate were not affected by adding water in sandy grassland of Keerqin sand lands. Net nitrogen mineralization rates ranged from 0.5 μg·g-1·month-1 to 4 μg·g-1·month-1. The highest values of soil inorganic nitrogen and net nitrogen mineralization occurred on October 15 in control plots. The seasonal changes of soil inorganic nitrogen contents exhibited "V" shape pattern that was related to seasonal patterns of soil ammonium-N (ascending trend) and nitrate-N transformation (descending trend). 相似文献
920.
In an alley cropping experiment, a study was carried out on N2 fixation by Gliricidia sepium, nitrogen (N) accumulation by prunings of Gliricidia, Senna siamea (formerly Cassia siamea) and Gmelina arborea, and the N contribution to associated crops of rice and cowpea.Total N accumulated by the hedgerow trees ranged from 297–524 kg N ha–1 on average but varied between tree species and depended on the growing season. Gliricidia sepium accumulated 370 kg N ha–1 on average and more than half of this came from fixation. Senna siamea and Gmelina arborea served as reference trees for estimating N2 fixation. The estimates of N2 fixation using Gmelina as a reference gave higher estimates than those using Senna.Although the dry matter and nitrogen yields of prunings from the hedgerow trees were high, their relative nitrogen contribution to the associated crops was generally low ranging from 5 to 29%. Higher crop yields and nitrogen contribution were observed with Gliricidia sepium prunings. The low N contribution from prunings was attributed to the lack of synchronization between the N released from the prunings and the crop's demand for N. 相似文献