不同利用情况对苇状羊茅+红三叶草地生产力的影响(1988～1989年)

对以苇状羊茅占优势的人工草地分别于生长第一二年进行利用比较试验,结果表明:始用期和始牧草层高度不同,对草地生产力、牧草越夏率及杂草侵染程度具有明显影响.     

紫花苜蓿混播研究进展

近年来,我国紫花苜蓿种植面积不断扩大。通过对紫花苜蓿、牧草混播优越性、牧草混播成员和比例的选择、刈割期和施肥等研究进行综述,并指出存在的不足,提出相应建议。     

鄂中丘陵苇状羊茅草地放牧强度试验(1989年)

我国南方10年来,开发利用草山草坡资源,建植人工草地初具规模,促进了草食畜牧业的发展,但因草地利用过重,部分草地出现退化.作者在鄂中丘陵区建植面积较大的苇状羊茅草地上,初步进行了放牧强度试验.试验表明:牧草生长季放牧率为1.8亩/只,草地利用率60%为较适宜的放牧强度,既能维持稳定的草地初级生产能力,又能控制苇状羊茅老化,供羊只获得较高的增重。     

条带式改良陡坡草地的水土保持效益

本文对条带式补播改良天然划坡的水土保持效益进行了研究。其结果表明,用条带式改良陡坡草地。其风干划产量较天然草地提高1.76～2.25倍,草群中豆科牧划的比重由原业的24.04％增加到75.46％,有毒有害植物明显减少,植被覆盖度由42.5％增加到83.5％,且改变了植物群落结构。改良草地的地表径流比天然草地减少13.14％,土壤冲刷减少28.08％,为有效地控制地表土壤水分和养分的流失创造了条件,提高了水土保持效益,并为黄土高原丘陵沟壑区陡坡划地的改良提供了依据。     

草地植物竞争的研究进展

对当前草地植物竞争的研究方法、模型和竞争系数进行了简要说明,对影响草地植物竞争的因素如温度、养分、水分、光照、刈割和植物构件等进行了详细阐述。     

Recolonization of methyl-bromide sterilized soils by plant and soil nematodes over 52 months

Recolonization of soils by organisms is dependent not only on biological factors but also on site factors including soil and vegetation. The total nematode populations in soil sterilized 52 months earlier with methyl bromide ranged from 77 to 123% of those in untreated soil; both vegetation and rainfall appear to have been important factors in the recolonization. In a high-rainfall pasture the dominant plant-feeding nematode Helicotylenchus did not recolonize and was replaced by Paratylenchus. Under high rainfall, Iotonchus failed to recolonize either pasture or forest, but Clarkus recolonized well. While indices such as the maturity index, the summed maturity index, PPI, the ratio of fungal: bacterial feeding nematodes, species richness, the Shannon-Weaver index, and indices of evenness, dominance, and diversity showed various effects, none gave consistent trends; rainfall and vegetation probably exerted too much influence. In the light of trends in our data, in data for other ecosystems, and the reality of r-K strategies in animals, it may not be reasonable to expect a global nematode index of soil health or ecosystem condition. While a nematode index may be useful in local or regional studies, research efforts may be better directed towards elucidating key populations of nematodes for investigating the impact of particular land management practices on ecosystem sustainability.     

Gross nitrogen mineralisation rates in pastural soils and their relationships with organic nitrogen fractions, microbial biomass and protease activity under glasshouse conditions

In this study, gross nitrogen (N) mineralisation rates were determined in six pasture soils (Fleming, Kairanga, Karapoti, Lismore, Templeton and Waikoikoi) from three different regions of New Zealand. The soils were kept under controlled soil water potential (–10 to –30 kPa) and temperature (12–20°C) conditions in a glasshouse. The gross N mineralisation rates ranged from 0.76 to 5.87 g N g^–1 soil day^–1 in the six soils and were positively correlated with the amount of amino acid-N (AA-N), ammonia-N (NH₃-N), total hydrolysable-N (TH-N), microbial biomass-carbon (MB-C), microbial biomass-N (MB-N), protease activity and organic C and N. A stepwise regression was used to generate equations that could best describe gross N mineralisation rates. Microbial biomass-carbon and AA-N were included in the equation that best described the gross N mineralisation rate:

Assessment of the influence of phosphate fertilizers on the microbial activity of pasture soils

The objective of the present work was to examine the effects of phosphate fertilizers on the microbial activity of pasture soils. Various microbial characteristics were measured using soils from an existing long-term phosphate fertilizer field trial and a short-term incubation experiment. The measurements included basal respiration, substrate induced respiration, inhibition of substrate-induced respiration by streptomycin sulphate (fungal activity) and actidione (bacterial activity) and microbial biomass C. The long-term field trials was initiated during 1985 to examine the effectiveness of different sources of phosphate fertilizers (single superphosphate, North Carolina phosphate rock, partially acidulated North Carolina phosphate rock, and diammonium phosphate) on pasture yield. The incubation experiment was conducted for 8 weeks using the same soil and the sources of phosphate fertilizers used in the field trial. In the incubation experiment the fertilizer addition caused an initial decrease in basal and substrate-induced respiration but had no effect on total microbial biomass. The initial decline in basal and substrate-induced respiration with the fertilizer addition was restored within 8 weeks after incubation. In the field experiment the fertilizer addtion had no significant effect on basal respiration but increased substrate-induced respiration and microbial biomass C. The short-term and the long-term effects of phosphate fertilizer addition on the microbial characteristies of the soils are discussed in relation to its effects on pH, salt concentration, and the nutrient status of the soils.     

Soil macrofaunal biodiversity in Amazonian pastures: Matching sampling with patterns

Soil biodiversity varies through space as influenced by habitat features and land-use history. The performance of any sampling strategy highly depends on its relevance with regards to this pattern. We surveyed the soil macrofaunal species richness in the pastures of the Benfica Field Station (Eastern Amazonia, State of Pará, Brazil) and described its variability in 4 independent replicate plots. We designed a within-plot sampling scheme that accounted for the soil spatial variation (stratified sampling). Replicated pasture plots had different species richness (49-65) corresponding to a low proportion (40-53%) of the total number of species (123). Pairs of replicated plots showed an outstandingly low number of shared species (28-41% of the species pool). Likewise, different classes of soil thickness, corresponding to a Ferralsol-Cambisol sequence, had different species richness (12-44) and exhibited a very low proportion of shared species (15-29%). The proportion of rare species, i.e. singletons, ranged from 40-51% of the total species richness depending on the plot considered. We used the abundance-based coverage estimator of species richness (ACE) and the Chao shared species estimator that provides a correction based on the relative abundance of rare species. These indices also showed both a high between plots dissimilarity and a substantial within plot variability of species composition. Because of the high proportion of rare species, the rarefaction curves failed to reach any asymptote in all replicated plots. Bootstrap resampling showed that less than 5 samples per stratum (class of soil thickness) provided inconsistent species richness values. We simulated the efficiency of sampling strategies that included our 4 replicate plots and the 3 classes of soil thickness but with varying sampling effort within each stratum. The results indicated that a fairly large (74%) proportion of species would be recorded if strata were sampled using 5 sampling units (hence 15 samples per plot for a total of 4×15=60 samples). This study showed the need for adequate plot replication in soil macrofaunal biodiversity studies. Also, the main relevant factors of within-replicate plot spatial heterogeneity (e.g. soil, vegetation) should be accounted for through stratified sampling. The results showed that there is no way of reducing the local sampling effort below a certain level (here, 5 sampling units per stratum).     

Biological nitrogen fixation in a grazed perennial grass/clover ley and correlation with herbage and soil variables

In a grazed grass/clover pasture, biological nitrogen fixation (BNF) is a source of nitrogen (N). The determination of this N input and how it is influenced by N, phosphorus (P) and potassium (K) in the soil, is complicated by grazing animals, which cause variation in defoliation and soil mineral content in both space and time. In a perennial grass/clover ley on a commercial Danish organic farm, exclusively grazed by dairy cows, we investigated BNF, clover proportion of the herbage, accumulated dry matter of clover and N, P and K concentrations in separates of clover and grass in relation to inorganic concentrations of N, P and K in the soil. The ¹⁵N natural abundance technique was used to determine the proportion of clover N derived from the atmosphere (pNdfa) using grass as a non-fixing reference. In September 1997, soil and biomass sampling was carried out on 81 randomly selected plots. The value of pNdfa was on average 0.6, ranging from 0.12 to 0.96 and BNF exhibited a significant but weak correlation (r=0.432) with accumulation of dry matter in clover. For the significant correlations, r varied between −0.403 and 0.648. The proportion of clover in the sampled herbage averaged 48%, ranging between 18 and 78%, but varied independently of BNF. Due to a high concentration of P and moderate to high concentration of K in the soil, clover and grass were well supplied with P and K, which was confirmed by the concentrations of K and P in shoot material.