The effects of nitrogen and fungicide on cereal aphid population development and the consequences for the aphid-yield relationship in winter wheat

In a field trial, done over two seasons, nitrogen and fungicide inputs to winter wheat were varied to obtain a range of yields to study the effects on aphid population development and the aphid-yield loss relationship. In the first year, the maximum density of Metopolophium dirhodum and total aphid index were significantly higher in the plots receiving the largest amount of nitrogen but there were few other consistent effects on aphid population development. In the second year there were no significant effects of either nitrogen or fungicide on aphid population development. Mean yields were high in 1987 and 1988 (7.0 and 8.5 t/ha respectively) with less than a 2 t/ha range in either year. There were no significant effects of aphids on yield in the first year but in the second, aphids caused a significant reduction. Damage per aphid unit did not change with increase in yield. The use of this approach in determining pest-yield loss relationships is discussed.     

Transgenic Arabidopsis leaf tissue expressing a modified oryzacystatin shows resistance to the field slug Deroceras reticulatum (Müller)

Transgenic Arabidopsis thaliana has been developed which expresses the oryzacystatin mutant OCI86, which is an inhibitor of the major proteinase present in the digestive gland of the slug, Deroceras reticulatum. When fed on leaf tissue from plants expressing this inhibitor the growth of juvenile slugs was significantly reduced by 31% compared with those feeding on control leaf tissue. Furthermore, while surviving slugs did not individually consume less when feeding on leaf tissue expressing OCI86, the total amount of leaf tissue eaten was 50% less, due to reduced survival of slugs. The synthetic cysteine proteinase inhibitors E64 and leupeptin also significantly reduced slug weight gain (by at least 40%) and digestive gland cysteine proteinase activity when administered in an artificial diet, indicating that their antimetabolic effects are due to direct inhibition of gut proteolytic activity. These results suggest that transgenic crop plants expressing phytocystatins could be used to suppress the growth rates of slug populations in the field.     

Effects of Nutrient Limitation on Aboveground Carbon Dynamics during Tropical Dry Forest Regeneration in Yucatán,Mexico

Tree growth (as diameter increment), litterfall production, and litter biomass were studied in two secondary tropical dry forests of the Yucatán Peninsula under four treatments of nutrient addition. The studys objective was to assess how variations in the nutrient supply affect aboveground net primary production and carbon (C) accumulation on the floor of two forests in different stages of regeneration. The study included an area of young forest (10 years old) with phosphorus (P)-poor soils and an area of old forest (around 60 years old) where soil P was comparatively less limiting. Four replicate plots (12 × 12 m) at each forest were either left intact (controls) or fertilized with nitrogen (N), P, or N plus P during 3 consecutive years. After 3 years of fertilization, relaxation of the constraints on nutrient limitation resulted in increased trunk growth rates at both the young and old forests. This effect was more pronounced with the addition of P or N plus P (trunk growth doubled with respect to controls), whereas N addition increased tree growth by 60% in comparison to trees in plots without nutrient supplements. In both forests, there were no significant differences in litterfall production among treatments during the first 2 years after fertilization. In the 3rd year of nutrient addition, litterfall production was significantly higher in plots fertilized with N plus P compared to control plots at both forest sites; however, changes in litterfall were not accompanied by litter accumulation in the floor of the two forests. The results of this study support the hypothesis that there is nutrient limitation during tropical dry forest regeneration. They further show that it may be maintained in the long term during secondary succession.     

作物最高理论产量计算方法的应用——以合肥地区水稻为例

本文以合肥地区水稻为例,探讨了作物最高理论产量的计算方法,即首先根据“ＦＡＯ”农业生态带理论,计算出作物光温生产力指数,再根据当地的气候（主要是水分状况）对作物的光温生产力指数进行订正,从而求出作物的最高理论产量。     

The potential benefits from cultivar specific red clover -potato crop rotations

The aim of this study was to determine if endophytic bacteria could contribute to cultivar specific interactions between red clover (Trifolium pratense L.) and potatoes (Solanum tuberosum L.) in crop rotations. Endophytic bacteria were isolated from the roots of four red clover cultivars (AC Charlie, Altaswede, Marino and Tempus) grown in the field. Populations of bacteria from each cultivar were similar. The most abundant genus was Rhizobium, but species of Curtobacterium, Pseudomonas, and Xanthomonas were common to all cultivars. Plantlets of two potato cultivars, Russet Burbank and Shepody, were inoculated individually with the seven bacterial isolates most frequently recovered from each red clover cultivar, and grown in Magenta vessels for 6 wk. Significant differences were found for plant height, and wet weights of roots, shoots and their total. Potato cultivars differed for root wet weight only, while red clover cultivar, as a source of bacteria, had a significant effect on all traits except plant height. Differences among bacteria were significant for all traits except shoot wet weight. There was a significant interaction of potato cultivar by red clover cultivar. The potato cultivar Russet Burbank did best with bacteria from the red clover cultivar, Marino; and Shepody, with bacteria from Altaswede.     

Early phosphorus nutrition,mycorrhizae development,dry matter partitioning and yield of maize

We conducted a field experiment to test the hypothesis that improved phosphorus nutrition occurs in maize plants with rapid arbuscular (AM) mycorrhizae development at early developmental stages and that this also is reflected in dry matter allocation and final yield. A split-split plot design was used with previous crop (Zea mays L.-maize and Brassica napus L.-canola), tillage practices (no-tillage or conventional tillage) and P fertilization (5 levels) as factors chosen to modify mycorrhizae development at early developmental stages of maize. Previous cropping with canola resulted in decreased shoot-P concentration and shoot growth of maize at early stages. No-tillage resulted in higher shoot-P concentration but lower shoot weight than conventional tillage. Greater shoot-P uptake was related to a rapid intraradical development of mycorrhizae (previous crop of maize) or rapid connection to a mycorrhizal mycelium network (no-tillage treatments). Maize yield and harvest index were lower after cropping with canola. The yield for conventional tillage was higher than that for no-tillage but the harvest index was lower. The hypothesis was supported at early stages of maize growth by the effect of previous crop but not by results of tillage, because an unknown factor reduced growth in the no-tillage system. The hypothesis was supported at maturity by increased biomass allocation to grain relative to total shoot weight in treatments with greater shoot-P concentration at early stages.     

Reducing Meloidogyne incognita Injury to Cucumber in a Tomato-Cucumber Double-Cropping System

The effects of a root-knot nematode-resistant tomato cultivar and application of the nematicide ethoprop on root-knot nematode injury to cucumber were compared in a tomato-cucumber double-cropping system. A root-knot nematode-resistant tomato cultivar, Celebrity, and a susceptible cultivar, Heatwave, were grown in rotation with cucumber in 1995 and 1996. Celebrity suppressed populations of Meloidogyne incognita in the soil and resulted in a low root-gall rating on the subsequent cucumber crop. Nematode population densities were significantly lower at the termination of the cucumber crop in plots following Celebrity than in plots following Heatwave. Premium and marketable yields of cucumbers were higher in plots following Celebrity than in plots following Heatwave. Application of ethoprop through drip irrigation at 4.6 kg a.i./ha reduced root galling on the cucumber crop but had no effect on the nematode population density in the soil at crop termination. Ethoprop did not affect cucumber yield. These results indicate that planting a resistant tomato cultivar in a tomato-cucumber double-cropping system is more effective than applying ethoprop for managing M. incognita.     

Field observations on nitrogen catch crops

Nitrogen catch crops help to reduce the loss of nitrogen from arable cropping systems during autumn and winter. The ability of catch crops to absorb nitrogen from the soil profile is affected by rate and depth of colonization of the soil by roots. The aim of the current work was to analyze total root length and root length density of catch crops in relation to above ground growth, nitrogen supply and crop species. In two field experiments roots were sampled with an auger. Experimental factors included crop species (winter rye, Secale cereale and forage rape, Brassica napus ssp. oleifera (Metzg.) Sinsk., or oil radish, Raphanus sativus spp. oleiferus (DC.) Metzg.), two sowing dates S1 and S2 (end of August and three weeks later) and two nitrogen treatments: N0, no nitrogen applied, and N1, nitrogen applied at non-limiting rate.The natural logarithm of the total root length, measured in the top 40 cm, L_0–40 (km m^-2), was linearly related to natural logarithm of the dry weight of the shoot, W (g m^-2). There was no effect of species or sowing date on this relation. For a given W, N1 treatments showed lower values of L_0–40 than N0 treatments. The decline in root length density, D (cm cm^-3), with depth, X (cm), was described with the function ln D = ln D₀ – qX, where D₀ is the value of D at zero depth and q the linear coefficient. D₀ was linearly related to L_0–40, without effect of species, time of observation or N supply. The ratio D₀/q, an estimate of the absolute root length, was 1.24 × L_0–40.Together the relations enable estimates to be made of total root length and of root length distribution with depth using shoot dry weight of catch crops and its change with time as input. The generation of such estimates of root distribution is necessary for model studies in which the efficacy of catch crops to prevent N losses is evaluated in relation to sowing dates, distribution of N in the soil profile and the distribution of rainfall in the season.     

Living on the edge: life‐history of olive baboons at Gashaka‐Gumti National Park,Nigeria

Baboons are the most successful and ubiquitous African primates, renowned for their behavioral and reproductive flexibility, which enable them to inhabit a wide variety of habitat types. Owing to a number of long‐term field studies, comparative behavioral, developmental, demographic, and life‐history data are available from several populations, but study sites show a heavy bias toward South and East African savannahs, with little research in West or Central Africa. Life‐history data from such areas are important if we are fully to understand the nature of the environmental factors that limit baboon distribution. Here, we present demographic data for olive baboons at Gashaka‐Gumti National Park (GGNP), Nigeria, collected from December 2000–February 2006, and use these data to test comparative models of baboon life‐history. The GGNP habitat, which includes large areas of rainforest, is an environment in which baboons are little studied, and rainfall is much higher than at previous study sites. GGNP troop size data are presented from censuses, as well as life‐history data for two troops, one of which is within the park and wild‐feeding (Kwano troop), whereas the other dwells at the park edge, and supplements its diet by crop‐raiding (Gamgam troop). Troop sizes at GGNP are small compared with other field sites, but fit within previously suggested ranges for baboons under these climatic conditions. Inter‐birth intervals in Kwano troop were long compared with most studied populations, and values were not as predicted by comparative models. Consistent with known effects of food enhancement, Gamgam troop experienced shorter inter‐birth intervals and lower infant mortality than Kwano troop. We indicate some possible factors that exclude baboons from true rainforest, and suggest that the clearing of forests in Central and West Africa for agricultural land may allow baboons to extend their range into regions from which they are currently excluded. Am. J. Primatol. 71:293–304, 2009. © 2009 Wiley‐Liss, Inc.