High Fertilizer Treatment Research Articles

Fertilization decreases species diversity but increases functional diversity: A three-year experiment in a Tibetan alpine meadow

The link between biodiversity and grassland productivity remains a central puzzle for both theoretical and applied ecologists. Little is known about the response of functional diversity (FD, i.e. the extent of trait differences between organisms in a given community) to increased grassland productivity following fertilization. Species diversity is often used as a surrogate for FD but evidence shows that FD is often independent from species diversity.We conducted a three-year (2004–2006) experiment in a Tibetan alpine grassland to examine the effect of fertilization on FD and SD, and its relationship with productivity. We measured specific leaf area, plant height and seed size for 32 species in control, low- and high-fertilization treatments over three years, and quantified three components of FD: functional richness (FRic), functional evenness (FEve) and functional divergence using Rao's index (FDrao).While SD decreased rapidly, as expected, both FRic and FDrao increased significantly with fertilization. Neither species evenness nor FEve was affected by fertilization. Aboveground biomass was not significantly correlated with SD, but it was significantly positively correlated with both FRic and FDrao, with the strongest correlations found in 2006 for FRic and in 2005 for FDrao.The results showed that FD and SD have opposite responses to short-term fertilization. The increased FD suggests enhanced niche differentiation between species remaining after fertilization, which caused species loss. This study highlights the importance of examining FD in assessing fertilization-induced biodiversity loss and its impacts on ecosystem functioning in grasslands.

FERTILITY RATE AND TIMING EFFECTS ON ORGANIC BLACK CURRANT GROWTH AND YIELD DURING ESTABLISHMENT

A study on Prince Edward Island was initiated to assess the impact of organic fertility amendment rate and timing treatments on the growth, yield, berry size and soluble solids of black currants (Ribes nigrum ‘Titania’). Bushes were planted in the spring of 2009 at two sites with black plastic mulch as a weed control without irrigation, and fertilized with seven fertility treatments in either the spring, the summer or split between spring and summer. Rates were 50, 100 and/or 150 kg estimated available N from a blend of crab meal and poultry manure (Nutriwave®). Yield and berry soluble solids were measured in 2010 and 2011. Plants at the site with leaf P and K deficiencies showed lower growth and yield (492-2,540 kg ha-1), but had significant differences in growth response to amendments compared with the site that had adequate levels of P and K, which had no significant difference among treatments in yield in 2011 (3,935-5,016 kg ha-1) or growth among treatments in any of the three years. Where significant differences in growth were found, the medium spring fertility treatment gave the greatest growth and yield, followed by the high spring fertility treatment. The high spring treatment had the highest growth in 2010, but the lowest growth and yield in 2011.

β-Carotene yield and productivity of orange-fleshed sweet potato (Ipomoea batatas L. Lam.) as influenced by irrigation and fertilizer application treatments

β-Carotene rich orange-fleshed sweet potatoes are increasingly used in community-based interventions aimed at addressing vitamin A deficiency, but are often cultivated in marginal soils and with sub-optimal agricultural inputs. The aim of the study was to determine (i) β-carotene content, β-carotene yield and water productivity at increments of water application, and, (ii) β-carotene content and β-carotene yield at increments of chemical fertilizer application for orange-fleshed sweet potato in separate field trials. β-Carotene content at the low irrigation treatment was between 15 and 34% higher than at optimal irrigation treatment. Increased water application brought about a two-fold increase in β-carotene yield per unit area. The best combination of β-carotene yield and water productivity (g β-carotene ha−1mm−1 water applied) was achieved at the intermediate (60%) irrigation treatment. Calculations showed that 1ha of orange-fleshed sweet potato produced at the intermediate water application at yield level of 24.6–28.4tha−1, can potentially provide 452–730 households (of six persons) with an adequate amount of vitamin A over a period of 180days. β-Carotene content was 14% higher for both intermediate (50%) and high (100%) fertilizer treatments, compared to the 0% fertilizer treatment. β-Carotene yield increased two-fold at the intermediate and four-fold at the high fertilization treatment. This paper provides novel information on the effect of irrigation on β-carotene yield, as well as β-carotene water productivity in orange-fleshed sweet potato. Follow-up research on a range of varieties is suggested toward obtaining recommendations for broad application in vitamin A crop-based interventions to optimize the β-carotene yield in orange-fleshed sweet potato.

Effect of Biological Organic Fertilizer on Plant Growth and Yield of Chinese Kale

A substrate culture experiment was conducted to study the effect of different biological organic fertilizer levels (control: zero fertilization, low level, medium level and high level) on plant growth and yield of Chinese kale (Brassica alboglabra Bailey). Results showed that compared with control, treatments of medium and high fertilization increased the leaf number, plant height, stem diameter, yield and plant dry matter of Chinese kale. Thus they promoted plant growth. The fertilizer utilization ratio of Chinese kale was the lowest for low fertilization treatment, and it was the highest for medium fertilization treatment, while it was decreased for high fertilization treatment. The treatment of medium level fertilization (30g/plant) promoted plant growth and increased the yield of Chinese kale; also it had the highest fertilizer use efficiency. So it was the appropriate organic fertilization amount for Chinese kale production.

Barriers to conducting clinical research in reproductive medicine: Australia and the United Kingdom

There are several major barriers to research in reproductive medicine in the United Kingdom and Australia. In Australia these mainly reflect income disparity between research and private practice whereas in United Kingdom they reflect the consequences of the economic downturn.

Influences from Long-Term Crop Rotation, Soil Tillage, and Fertility on the Severity of Rice Grain Smuts.

False smut (Ustilaginoidea virens) and kernel smut (Neovossia horrida) are diseases of rice (Oryza sativa) that reduce both grain yield and quality. Susceptible rice cultivars are in widespread use on production acreage in the United States, and the effects from crop management practices on smut control are poorly understood. We studied the long-term effects of crop rotation, soil tillage, and fertility level on rice smut severity. The highest levels of false smut observed in this study were on cultivars grown in rotation with soybean, on traditionally tilled soils, with high fertilizer treatments. The highest levels of kernel smut were observed in a rice-soybean rotation with winter wheat grown between summer crops. These rotations are commonly used in rice-growing regions of the southern United States. Using combinations of crop rotation, soil tillage, and fertility rate, several alternative crop-management practices were identified that provided effective control of smuts in susceptible rice cultivars. The most effective method for controlling both false smut and kernel smut was in 3-year rotations of rice, soybean, and corn. Regardless of rotation order or tillage and fertility treatments within the rotations, rotating out of rice for 2 years was the most effective approach for smut control.

Fertilizer Composition, Concentration, and Irrigation Method Affect Growth and Development of Oxalis regnellii and O. triangularis

Oxalis regnellii, the shamrock plant, and O. triangularis are niche ornamental greenhouse crops produced and marketed primarily for their foliage; thus, it is imperative to produce the fullest, most colorful, and blemish-free plants as possible. An experiment was conducted using O. regnellii, comparing two irrigation methods, overhead (drip) irrigation versus subirrigation, in addition to varying 20N–2.2P–16.6K fertilizer concentrations, 50, 100, 200, 300, and 500 mg·L−1 nitrogen (N). Overhead irrigation produced larger plants with increased root mass as compared with subirrigation. Low or high fertilizer concentration (50 mg·L−1 N and 500 mg·L−1 N, respectively) led to reductions in the fresh and dry weight of overhead-irrigated plants compared with intermediate fertilizer rates. At the highest fertilizer treatment, plant height was decreased. Chlorophyll index (based on SPAD readings) increased linearly and quadratically for subirrigated and overhead-irrigated plants, respectively. A second study analyzed the effects of seven different fertilizer formulations on growth of O. regnellii and O. triangularis. The fertilizers used in this study were Jack's LX All Purpose (21N–2.2P–16.6K), Peter's Professional (20N–8.8P–16.6K), Jacks Poinsettia FeED Ca-Mg (15N–1.7P–12.5K), Jack's Petunia FeED Mg (20N–1.3P–15.7K), Peter's Professional Peat-Lite Dark Weather Feed (15N–0P–12.5K), Peter's Excel Cal-Mag (15N–2.2P–12.5K), and the slow-release fertilizer Osmocote® (14N–4.2P–11.6K). Growth of both species was significantly reduced by fertilizers that contained little or no phosphorus (P). Current water-soluble fertilizer recommendations of 21N–2.2P–16.6K or slow-release granule fertilizer of 14N–4.2P–11.6K (Osmocote®) produced acceptable, marketable plants, whereas the best O. regnellii and O. triangularis plants were produced using 15N–2.2P–12.5K and 20N–1.3P–15.7K formulations, likely as a result of the additional calcium (Ca), magnesium (Mg), and iron (Fe) in the mixtures.

Effects of contrasting soil fertility on root mass, root growth, root decomposition and soil carbon under a New Zealand perennial ryegrass/white clover pasture

The contribution of below ground plant root tissue to soil carbon (C) pools is attracting considerable interest in the context of greenhouse gas mitigation options. A field experiment was conducted on a perennial ryegrass/white clover pasture in the Manawatu, New Zealand, to examine the effect of differing soil nitrogen (N) and phosphorus (P) fertility status on root dynamics. Root standing mass, shoot and root dry matter (DM) accumulation and root tissue decomposition were measured at 6–8 week intervals over one year at moderate (Olsen P = 24, no added N) and high (Olsen P = 49, 400 kgN ha−1y−1 added N) soil fertility levels. Shoot production was significantly greater in the high fertility treatment (2550 cf. 1890 gDM m−2y−1) but differences in root dynamics were confined to two periods in spring and winter. In late spring the pattern was for lower root mass (183 cf. 231 gDM m−2 between 0–80 mm depth) and higher root production (0.71 cf. 0.52 gDM m−2 d−1 between 0–120 mm depth) under higher fertility. In winter the reverse was observed. There is some evidence that the soil type used in the root in-growth cores underestimated root production values for this site by a factor of approx. one third. Short-term differences between the two fertiity treatments in standing root mass and root production did not lead to treatment differences in topsoil C and N changes over four years. This may reflect insufficient separation in the two soil fertility treatments and a low overall root tissue input to soil organic matter.

Effect of Selenium Fertilization and Methyl Jasmonate Treatment on Glucosinolate Accumulation in Broccoli Florets

Broccoli (Brassica oleracea ssp. italica) is a rich source of glucosinolates (GSs), phytochemicals that are hydrolyzed into isothiocyanates with known human anticarcinogenic bioactivity. Increasing dietary intake of the element selenium (Se) can also reduce the risk of cancer. Previous research reported that Se fertilization at high concentrations reduces the concentration of GSs in brassicaceous plants. This research was conducted to determine the effect of Se fertilization on accumulation of different types of GSs in broccoli floret tissues in five genotypes. Methyl jasmonate (MeJA), an elicitor known to stimulate biosynthesis of indolyl GSs, was used to analyze changes in biosynthetic capability of indolyl GSs in broccoli floret tissue under Se-enriched conditions. Five broccoli genotypes were subjected to root fertilization with low and high levels of Na2SeO4 solutions (0.17 and 5.2 mm), MeJA sprays to aerial portions of the plants (250 μM), and the combined treatment of 5.2 mm Se with 250 μM MeJA, respectively. The effect of Se fertilization on GS accumulation varied among genotypes and the level of Se fertilization. Variation in the level of Se fertilization resulted in a dose-dependent decrease in glucoraphanin concentrations with no significant effect on indolyl GS accumulation in broccoli florets across the five genotypes. MeJA treatment increased indolyl and aromatic GS accumulation in floret tissues. MeJA-mediated increases in these GSs were inhibited in the high Se fertilization treatment, but the increase in neoglucobrassicin concentrations was less affected than other GSs in florets across the five genotypes. An experiment conducted with 6-week-old broccoli plants under the high Se treatment demonstrated greater accumulation of Se with depressed accumulation of sulfur and complete inhibition of MeJA-mediated indolyl GS accumulation compared with those changes in florets of mature broccoli plants. These results suggest that GS accumulation under Se fertilization may be influenced by not only the level of Se fertilization, but also the differences in sizes of available pools of resources (sulfur and sulfur-containing amino acids) required for GS biosynthesis and accumulation in broccoli plants. Partitioning of the variance indicated that the existence of substantial variability in GS concentrations was primarily attributed to differences in genotype response across different treatments. Results suggest that cultivar selection and breeding of broccoli can be used to develop broccoli germplasm with enhanced capacity for Se uptake and stability of GS biosynthesis with varying Se fertilization.

Responses of soil water balance and precipitation storage efficiency to increased fertilizer application in winter wheat

Increased fertilizer use over many years may have detrimental effects on crop production due to its high soil water consumption in rainfed regions. In this study, based on a long-term fertilization experiment initiated in 1984, we report the effect of increased fertilization on soil water balance, precipitation storage efficiency (PSE), yield and water use efficiency of winter wheat from 2005 to 2009. The experimental design consisted of a control treatment (CK) and three fertilizer treatments: nitrogen, phosphorus and manure (NPM), nitrogen and phosphorus (NP), and nitrogen (N). Soil water storage in NP and NPM was significantly lower than that in CK and N at both harvest and planting time. Compared with the CK, on average, treatments N, NP and NPM increased soil water recharge during the fallow period by 11%, 22% and 17%, and they also increased soil water depletion during growing season by 17%, 23% and 23% (P < 0.05), respectively. The average value of annual soil water balance was positive for all treatments, and was not significantly different among treatments. Increased fertilizer application significantly (P < 0.05) increased PSE during the summer fallow periods, and the average PSE was 28%, 32%, 34% and 33% for CK, N, NP and NPM, respectively. Wheat yield and water use efficiency increased significantly after long term fertilization, especially for treatments NP and NPM. The results indicated that more of rainfall was used for evapotranspiration and less was lost during the fallow season for the high fertility treatments after long term fertilizer application. In the long run, such changes in water use pattern could help to improve the sustainability of winter wheat production.

Ingestion and excretion of nitrogen by larvae of a cabbage armyworm: the effects of fertilizer application

1 Insect frass has significant impacts on decomposition and soil nitrogen dynamics. Although the frass contains various forms of nitrogen that may differently influence nitrogen dynamics in the decomposition process, how the nitrogen form in the insect frass is influenced by host plant quality remains poorly understood. 2 The present study examined the effects of application of fertilizer on leaf quality of Brassica rapa L. var. perviridis Bailey (Brassicaceae), and on the consumption, frass excretion and frass quality of its insect pest Mamestra brassicae (L.) (Lepidoptera: Noctuidae), with a particular focus on the dynamics of inorganic nitrogen. 3 Brassica rapa increased total nitrogen concentration, and accumulated inorganic nitrogen [i.e. leaf nitrate-nitrogen (NO3−-N) and ammonium-nitrogen (NH4+-N)] in the leaves in response to the application of fertilizer. 4 Although leaf consumption and frass excreted by M. brassicae was not affected by fertilizer treatment, frass quality was influenced by host plant quality as altered by fertilizer applications. Frass contained high concentrations of total nitrogen, NO3−-N, and NH4+-N under high fertilizer treatment. In particular, the larvae excreted much more NH4+-N than ingested. The relationship between host plant quality and insect frass quality, as well as the potential implications for decomposition and nutrient dynamics, are discussed.

Nitrogen fertilization affects the growth performance, betaine and polysaccharide concentrations of Lycium barbarum

Lycium barbarum, also known as Goji, is a popular medicinal plant in the traditional Chinese medicine. The present study aimed to examine the effects of nitrogen (N) fertilization on the growth performance, betaine and polysaccharide concentrations in different plant parts of L. barbarum. L. barbarum seedlings were subjected to organic (Org 1: 15 g N pot −1; Org 2: 30 g N pot −1) and chemical (Chem 1: 2.5 g N pot −1; Chem 2: 5 g N pot −1) N fertilizer treatments, followed by collecting the plant materials for chemical analysis. Results showed that the yield and uptake of N in plants of Org 2 (high organic fertilizer) treatment were the highest. Although plants of Chem 2 (high chemical fertilizer) treatment demonstrated to contain the highest N concentration, its yield in biomass was the lowest. A decrease in soluble sugar, polysaccharide and betaine concentrations was noted with increasing application of chemical N fertilizer. However, an increase in the organic N fertilizer favors the betaine synthesis. Taken together, these results conclude that L. barbarum responded differently to the type of fertilizers, with the increase application of N fertilizer lead to a decrease in polysaccharide concentration whilst enhancing the betaine synthesis.

Effects of Host Quality on Flight Muscle Development inNeochetina eichhorniaeandN. bruchi(Coleoptera: Curculionidae)

Neochetina eichhorniae Warner and N. bruchi Hustache, biological control agents of Eichhornia crassipes (Martius) Solms-Laubach, are usually incapable of flight but occasionally develop indirect flight muscles enabling dispersal. This reportedly alternates with oögenesis and is reversible. We examined host quality as a possible explanation for the transitions between these 2 states by allowing populations of the 2 species to develop on plants differing in nutritive quality and then examining the status of their ovaries and flight muscle development. The leaf nitrogen content of the plants increased directly with fertilizer treatment levels but herbivory by the weevils changed the pattern of variation. Neochetina eichhorniae suppressed overall nutritive quality while still enabling tissue nitrogen levels to increase with fertilizer treatments. Neochetina bruchi, however, negated these effects and tissue nitrogen levels failed to correlate with fertilizer treatments. As a result, herbivore intensity (the number of weevils per plant) and the proportion of the populations that responded in one way or the other (either oögenesis or flight muscle development) differed between the 2 species. Very few N. eichhorniae responded in the lowest fertilizer treatment and none produced flight muscles. This increased in the intermediate treatments to about an 80% response with most individuals reproductive. At higher levels, the overall response declined somewhat with an increasing proportion becoming dispersive. Very few N. bruchi developed flight muscles except in the highest fertilizer treatment. The frequency of reproductive N. bruchi varied little across fertilizer treatments, tracking host quality instead. We conclude that transitions from reproduction to dispersal in these 2 species are not in response to low nutritive quality of the plant tissue and require adequate nutrition to occur. Host quality, however, is affected by a multitude of factors, including the intensity of herbivory, which complicates interpretation of nuanced responses.

Using Assembly Theory to Explain Changes in a Weed Flora in Response to Agricultural Intensification

The intensification of crop management in the U.K. over the past 60 years has resulted in the decline of the populations of a number of annual plant species adapted to arable habitats. In contrast, other species continue to be common as arable weeds. A community assembly approach was taken to explain these recent changes in the weed flora using databases of plant functional traits, a pot experiment, and weed surveys of the Broadbalk long-term experiment. The hypothesis was tested that species that have been selected against by increased fertilizer inputs and herbicide use share an adverse combination of traits. An analysis comparing the combination of maximum height, seed weight, and time of first flowering of 29 common and 32 rare or threatened U.K. autumn weeds established that rare or threatened species occupied an area of trait space that was distinct from the common species. A rare weed trait syndrome of short stature, large seed, and late flowering was identified. The theory that species with a trait syndrome that is currently unfavorable are better adapted for less fertile environments was supported by the pot experiment. Species with a combination of short stature and large seed had a relatively greater competitive ability in low compared to high fertility treatments. Analysis of survey data from the Broadbalk long-term experiment confirmed that, as N inputs increased, the abundance of the two functional groups that contained only common species remained stable or increased; whereas, the groups dominated by rare or threatened species declined as fertility increased. An understanding of the response traits of arable plants to management filters, including fertilizer inputs and herbicide, is valuable for designing conservation strategies for rare species or predicting future shifts in the functional diversity of weed communities including the potential for invasive species to establish.

Water-use efficiency and physiological responses of maize under partial root-zone irrigation

Alternate partial root-zone irrigation (APRI) is a water-saving irrigation method but also can regulate crop physiological responses. This study investigated how water-use efficiency (WUE) and other physiological responses were regulated at different growth stages when maize plants were applied with APRI and how these responses were recovered to control levels when full irrigation was resumed. A pot experiment was carried out at two fertilization levels and with three irrigation methods at the jointing stage (29–38 days after sowing) or during the jointing and tasselling stages (29–77 days after sowing). The irrigation methods included the conventional irrigation (CI), APRI and fixed PRI (FPRI, watering was fixed to one side). Compared to the CI, APRI at the jointing stage for 10 days or during the jointing and tasselling stages for 49 days reduced water consumption by 10.6–12.9 and 31.7–32.4%, respectively, but did not reduce total dry mass accumulation significantly, thus increased canopy WUE by 10.4–13.6 and 41.2–41.8%, respectively. FPRI reduced the total dry mass significantly even though it also improved canopy WUE. APRI had slight effect on the leaf relative water content (RWC), chlorophyll (Chl), carotenoid (CAR), proline (Pro) and malondialdehyde (MDA) contents and superoxide dismutase (SOD) and peroxidase (POD) activities from jointing to tasselling stages but recovery to the levels of CI was rapid after receiving full watering. In comparison, FPRI treatment significantly reduced leaf RWC, Chl and CAR contents and SOD and POD activities and increased the Pro and MAD contents. After receiving full watering, the above-mentioned physiological indexes in FPRI could not recover fully to the levels of CI. High fertilization treatment only increased leaf Chl content significantly and contributed little to the total dry mass accumulation. Our result suggests that APRI can make plants use water and nutrients more efficiently with better drought tolerance.

Bottom-up control of water hyacinth weevil populations: do the plants regulate the insects?

1. Nutrient availability varies widely in aquatic systems and is likely to profoundly affect the outcomes of plant–herbivore interactions in aquatic environments. This has implications in programmes aimed at the biological control of water weeds. We hypothesized that nutrient flux seasonally affects ovarian development of two specialist weevil species, Neochetina eichhorniae and Neochetina bruchi, thereby influencing population growth on the floating plant Eichhornia crassipes. 2. We also hypothesized that the weevils differed in their sensitivities to nutritional quality and interacted differently depending on host quality. 3. To test these hypotheses, we cultured E. crassipes plants under 20 fertilizer regimens then introduced reproductively dormant, over-wintering female weevils as single or mixed species populations. They were later retrieved and dissected to ascertain ovarian status. F1 progeny was extracted biweekly to compare fecundity with population growth. 4. Ovaries regained functionality and the reproductive proportion of the population increased with fertilizer rate as did the fecundity of reproductive individuals. F1 progeny increased exponentially from 7 to over 300 weevils tank−1 in the highest fertilizer treatment. 5. Mixed species treatments produced more offspring under high fertilizer rates than single species treatments (236 ± 32 mixed vs. 155 ± 25 N. bruchi or 170 ± 33 N. eichhorniae pure). Neochetina eichhorniae was more productive throughout than N. bruchi, but N. bruchi performed nearly as well in high fertilizer treatments. 6. Ratios of the two species remained consistent whether in single or mixed species populations suggesting a lack of interspecific interference. However, N. eichhorniae seemed more adaptable to a wider range of plant quality and more tolerant of lower nutritional circumstances. 7. Synthesis and applications. The coupling of reproductive status of the parental generation with the population response of the F1 generation indicates that plant quality drives population growth of both weevil species, demonstrating bottom-up regulation. This largely explains the variable performance of these weevils as biological control agents. These results emphasize the importance of considering bottom-up regulation in evaluating host range trials, predicting efficacy and in post-release evaluations. In addition, they suggest that partial herbicide treatments to accomplish phased removal of infestations could enhance the quality of the remaining plants, thereby better integrating biological control into current E. crassipes management systems.

Effect of fertilization dose and sowing density on grain-filling in different winter wheat cultivars

为确定施肥量和种植密度对不同品种小麦灌浆特性的影响, 采用多因素随机区组设计试验方法, 对优质冬小麦“陇鉴301”、“宁麦5号”和“1R17”的籽粒灌浆特性进行了研究, 应用Logistic方程对灌浆进程进行了拟合, 并就施肥量、种植密度和品种3因素进行了方差分析。结果表明：不同肥密水平下小麦灌浆进程符合Logistic生长曲线, 呈“慢－快－慢”“S”型变化。肥密水平对3品种12项灌浆参数均产生影响, 但影响的具体参数和影响程度因品种而异。在高密度高肥处理下, “陇鉴301”、“宁麦5号”较为适应, 产量最高(4 188.09 kg·hm^-2, 3 789.89 kg·hm^-2)；高密度中肥处理下, “1R17”最为适应, 产量最高(3 018.18 kg·hm^-2), 且灌浆过程达到最佳状态。不同品种肥密互作效应达极显著水平, 具有正向的互作值。为提高小麦产量, 生产上应依据不同基因型品种的特性来确定施肥量和种植密度。

Effect of Saturated Near Surface on Nitrate and Ammonia Nitrogen Losses in Surface Runoff at the Loess Soil Hillslope

Water pollution from agricultural fields is a global problem and cause of eutrophication of surface waters. A laboratory study was designed to evaluate the effects of near-surface hydraulic gradients on NO3–N and NH4–N losses in surface runoff from soil boxes at 27% slope undersimulated rainfall of a loess soil hillslope. Experimental treatments included two near-surface hydraulic gradients (free drainage, FD; saturation, SA), three fertilizer application rates (control, no fertilizer input; low, 120 kg N ha-1; high, 240 kg N ha-1), and simulated rainfall of 100 mm h-1was applied for 70 min. The results showed that saturated near-surface soil moisture had dramatic effects on NO3–N and NH4–N losses and water quality. Under the low fertilizer treatment, average NO3–N concentrations in runoff water of SA averaged 2.2 times greater than that of FD, 1.6 times greater for NH4–N. Under the high fertilizer treatment, NO3–N concentrations in runoff water from SA averaged 5.7 times greater than that of FD, 4.3 times greater for NH4–N. Nitrogen loss formed with NO3–N is dominant during the event, but not NH4–N. Under the SA condition, the total loss of NO3–N from low fertilizer treatment was 34.2 to 42.3% of applied nitrogen, while under the FD treatment that was 3.9 to 6.9%. However, the total loss of NH4–N was less than 1% of applied nitrogen. These results showed that saturated condition could make significant contribution to water quality problems.

Interactive effects of clipping and nutrient availability on the compensatory growth of a grass species

Resource availability is an important factor affecting the capacity of compensatory growth after grazing. We performed a greenhouse experiment with Poa bulbosa, a small perennial grass of the Mediterranean and Central Asian grasslands, to test the importance of nutrient availability for compensatory growth after clipping. We also compared the results with predictions of the limited resource model (LRM). Plants were grown at low and high fertilization levels and subjected to a clipping treatment. Contrary to the LMR, we found that in Poa plants compensatory growth occurred under the high fertilization level, while it did not occur under the low level. The LMR predicts a higher tolerance for grazing in the stressful environment. Our plants showed a significant decrease in their relative growth rates (RGR) after clipping. Although the plants allocated a 32–188% greater fraction of the mass to lamina growth after clipping, this greater allocation to the leaves did not fully compensate for the initial reduction in leaf area ratio (LAR). A sensitivity analysis showed for the clipped plants under the high fertilization treatment, that changes in leaf allocation (flam) enabled the plants to compensate for a part of the potential loss caused by defoliation. Probably, the increased biomass allocation comes largely from the bulbs. We conclude that the inconsistency of the LRM with our results originates in the lack of compensatory mechanisms in the model. To better understand how environmental conditions affect tolerance to herbivory, the effects of compensatory growth should be taken into account.

Fertilizer affects the behaviour and performance of Plutella xylostella on brassicas

Abstract1 Foliar nitrogen concentration, which can be manipulated in crop plants by fertilizer supply, has long been recognized as a major factor in phytophagous insect abundance and performance. More recently, the type of fertilizer supplied has been shown to influence the abundance of some herbivore species. The diamondback moth Plutella xylostella is a global pest of Brassica crops. Although it has been the subject of numerous studies on host‐plant resistance and pest control, few studies have addressed the effect of abiotic factors, such as nutrient supply, on its performance and behaviour.2 We assessed oviposition preference, larval feeding preference and larval performance of P. xylostella on two cultivars of Brassica oleracea. Plants were grown using two fertilizer types, John Innes fertilizer and an organic animal manure, at high and low concentrations.3 Plutella xylostella laid more eggs on cultivar Derby Day than Drago. Derby Day was also the cultivar on which larval performance was maximized. However, differences in larval performance between cultivars were only found when plants were grown in compost with John Innes fertilizer, and not when fertilized with animal manure.4 Foliar nitrogen concentration was greater in plants grown in high fertilizer treatments but did not differ between cultivars. The concentrations of three glucosinolate compounds (glucoiberin, sinigrin and glucobrassicin) were greater in the high fertilizer treatments. Glucosinolate concentrations were higher in the Drago than the Derby Day cultivar.5 These results are discussed in relation to the preference‐performance hypothesis, and the assessment of plant resistance differences between cultivars using different types of fertilizer.