Grass Plots Research Articles

Soil nitrous oxide emissions associated with conversion of forage grass to annual crop receiving annual application of pig manure

The disruptive land-use change during forage grass conversion to annual crop can be critical for determining nitrous oxide (N2O) emissions, but this is an understudied period. We measured soil N2O fluxes (using closed static vented chambers) together with potential environmental drivers of these fluxes from liquid pig manure (LPM) and solid pig manure (SPM) applied to an annual crop (ANN) and perennial forages (FPP) that was converted to annual crop. Unamended plots were used as a control (CON). The results showed that in 2013, average soil nitrate-N was significantly higher on the recently converted FPP (ranging from 19 to 83 mg N kg−1) than the continuous ANN plots (from 16 to 35 mg N kg−1). The recently converted perennial forage system produced three times greater N2O than the continuous annual system, which is likely a result of accelerated N mineralization from the accumulated soil organic matter (over 4 yr) and grass residues of the recently killed forage grasses. However, during the second year of the study when the FPP plots were reseeded to perennial grasses, the system emitted 30% less N2O than the ANN system. These results suggest that including perennial forage grass in rotation with annual crops can provide N-saving and climate change mitigation benefits; however, some of the N stored in the soil would be lost when the perennial grass plots are cultivated to grow annual crops.

The effect of intensive grazing systems on the rising plate meter calibration for perennial ryegrass pastures

The rising plate meter (RPM) is used to measure grass height, which subsequently is used in a calibration equation to estimate herbage mass (HM), an important parameter for optimization of feed management in grazing systems. The RPM is placed on the sward and measures the resistance of the sward toward the plate, which depends not only on grass length, but also on sward structure. The accuracy of the calibration equation for the RPM to estimate HM across grazing systems, however, has not yet been evaluated. Therefore, our aim was to analyze the effect of intensive grazing systems on RPM calibration for perennial ryegrass pastures. To do so, we studied 2 grazing systems: compartmented continuous grazing (CCG) and strip grazing (SG), which differ in key grazing characteristics, such as pre- and post-grazing heights and period of regrowth, that may influence tiller density and vertical flexibility of the sward. The experiment was performed from April until October in 2016 and 2017 with 60 dairy cows, at a fixed stocking rate of 7.5 cows per hectare. To calibrate the RPM, 256 direct measurements of HM >4 cm (i.e., above stubble) were collected by cutting and weighing plots of grass for CCG and SG. Our main interest was in the HM above stubble because this is consumed by cows. Herbage mass <4 cm represents the stubble left after grazing. Differences in HM <4 cm may (partially) explain differences in HM >4 cm between the grazing systems. Therefore, HM <4 cm was additionally measured on 4 out of every 8 plots per grazing system by cutting out quadrats to 0 cm with an electric grass trimmer. Our results showed an average error margin in our calibration equations of 25 to 31%, expressed as the root mean square error of prediction (RMSEP) as a percentage of the observed HM >4 cm. Differences between grazing systems were relatively small, and including grazing system as a factor in the regression model to explain the increase in HM per centimeter of grass did not reduce the RMSEP of the model to any relevant extent. On the other hand, HM <4 cm was significantly greater on CCG compared with SG, with 2,042 kg of DM per hectare for CCG and 1,676 kg of DM per hectare for SG. The HM <4 cm, however, is not used for grazing, and this difference was not reflected in the HM >4 cm. Our results indicate that we can use one region-specific calibration equation for perennial ryegrass pastures across intensive grazing systems, despite relatively large differences in pre- and post-grazing heights and period of regrowth.

Soil phosphorus dynamics following land application of unsaturated and partially saturated red mud and water treatment residuals

The secondary use of P-sorbing industrial by-products as a fertilizer or soil conditioner is gaining increased attention, particularly in light of diminishing reserves of rock phosphate traditionally used to manufacture P fertilizer. This study examined applications of red mud (RM) and water treatment residuals (WTR) at two levels of P saturation (i.e. ‘as received’ and partially saturated) in a soil incubation and runoff plot study. When incubated with soils ranging in texture and initial P concentration, P-sorbing residuals that were less enriched with P decreased water-extractable soil P (WEP) concentration to a greater extent than more P saturated residuals. In contrast to WTR treatments, not all of the RM applications decreased soil WEP concentrations below those of the control soils. The runoff study investigated soil P dynamics when partially P-saturated RM and WTR's were surface applied to grass plots at 2 t ha−1 on Day 0, followed by three rainfall simulations (7 cm h−1 for 30 min, Days 2, 7 and 28) and at 3 t ha−1 on Day 70 followed by two more rainfall simulations (Days 77 and 96). Application of residuals at these rates did not significantly increase dissolved reactive P (DRP) in runoff compared with unamended controls during the study. Forage cuttings taken 90 days after the first rainfall simulation indicated that nutrient uptake was not compromised by the application of the residuals. Overall results indicate that WTRs may be a more suitable soil amendment than RM residuals given their greater ability to reduce soil WEP across a range of soils without simultaneously increasing Mehlich-3 extractable soil P concentrations above the upper threshold limit (150 mg P kg−1), and their minimal impact on plant nutrient uptake.

English

In this paper, we evaluated the Water Erosion Prediction Project (WEPP) model using 5-yr monitored runoff and sediment data from three different lands cover treatments in the Loess Plateau of China. The results showed that the WEPP model was able to predict 22 out of 37 recorded runoff producing events, and 20 out of 34 recorded sediment producing events. Prediction of annual runoff is more accurate than the prediction of sediment. The correlation coefficients between the annual monitored and simulated runoff ranged from 0.69 to 0.91, and 0.11 to 0.90 for sediment; for the three treatments (bare, corn and grass), the prediction for the grass plot is better than the other two. Soil moisture and storm intensity appeared to have greater effect on both predictability and accuracy of runoff events and sediment yields. For grass plot, Nash-Sutcliffe coefficient was 0.76 in runoff and 0.56 in sediment. WEPP predictions for the grass plot were in agreement with measured values, but no better than using the averaged measured values for the other two treatments (bare and corn plots). Application of the WEPP model should be decided with precautions in the Loess Plateau area

The Effect of Contrasting Moistening Regimes on CO2 Emission from the Gray Forest Soil under a Grass Vegetation and Bare Fallow

The effect of contrasting moisture regimes on the CO2 emission from the gray forest soils (Haplic Luvisols (Loamic, Cutanic, Humic)) under a grass vegetation and bare fallow was studied in a field simulation experiment in June–September, 2015 (Moscow region). Two short soil droughts (53 and 34 days) and a long one (94 days) were simulated on plots isolated from precipitation. A variant with regular irrigation, where the soil moisture was maintained 60–70% of their water holding capacity, was used as a control. Over the whole observation period, the CO2 emissions from the soils studied decreased by a factor of 1.8 compared to the control only in the variant with the grass vegetation under prolonged drought. During the first hours after irrigation of the dry plots, the soil respiration intensified due to the “Birch effect”. The magnitude of this effect was 84–104% in the soils under the grass vegetation and 114–133% in the fallow areas. Owing to this phenomenon, the total CO2 emission from the soils subjected to two short droughts was equal to the CO2 flux under regular moistening for the grass plots and exceeded it by almost 1.3 times for the fallow plots as compared to the control. However, the share of extra CO2 flux induced by moistening of the dry soils did not exceed 8–10% of the total CO2 emission over the whole observation period.

Diagnosis of apple replant disease (ARD): Microscopic evidence of early symptoms in fine roots of different apple rootstock genotypes

Apple replant disease (ARD) is a problem of high economic relevance in tree nurseries and apple orchards worldwide. After replanting, plants show growth reduction, reduced yield, and damaged root systems. The disease’s decade-long persistence in soil exacerbates the situation where alternative cultivation areas and ecologically safe soil decontamination measures are lacking. The etiology is still unclear and there are neither clear causal factors nor reliable parameters (except growth data from plant bioassays) for the early detection of the disease in plants or from samples from potentially affected soils. We report on greenhouse pot trials with the susceptible rootstock Malus domestica ‘M26’ grown in soils of ARD-affected as well as grass plots from three different field sites. Both gamma-irradiated ARD soils and grass soils served as control soils. The aim was to develop a diagnostic tool for the early detection of ARD. In fine roots of first to third order, we assessed the root structure, the root hair density, the cellular damages in the outer layers, and the cell vitality. After only two weeks in ARD soil, ‘M26’ reacted with cell necroses and blackening in a characteristic pattern, impaired root hair development, and low cell vitality. These symptoms were confirmed in Malus domestica ‘Bittenfelder’ and Malus-hybrid B63. Root systems grown in gamma-irradiated soils were almost symptom-free while those from grass soils showed different and only minor alterations. Thus, we suggest selected fine root symptoms to be used for an early diagnosis of ARD, e.g. in plant breeding selections and soil surveys.

Evidence for functional state transitions in intensively-managed soil ecosystems

Soils are fundamental to terrestrial ecosystem functioning and food security, thus their resilience to disturbances is critical. Furthermore, they provide effective models of complex natural systems to explore resilience concepts over experimentally-tractable short timescales. We studied soils derived from experimental plots with different land-use histories of long-term grass, arable and fallow to determine whether regimes of extreme drying and re-wetting would tip the systems into alternative stable states, contingent on their historical management. Prior to disturbance, grass and arable soils produced similar respiration responses when processing an introduced complex carbon substrate. A distinct respiration response from fallow soil here indicated a different prior functional state. Initial dry:wet disturbances reduced the respiration in all soils, suggesting that the microbial community was perturbed such that its function was impaired. After 12 drying and rewetting cycles, despite the extreme disturbance regime, soil from the grass plots, and those that had recently been grass, adapted and returned to their prior functional state. Arable soils were less resilient and shifted towards a functional state more similar to that of the fallow soil. Hence repeated stresses can apparently induce persistent shifts in functional states in soils, which are influenced by management history.

Induction and diagnosis of apple replant disease (ARD): a matter of heterogeneous soil properties?

Abstract Apple replant disease (ARD) occurs when apple or a closely related species are replanted at the same site leading to severe growth reduction and losses in fruit yield and quality. This complex disease phenomenon is a worldwide problem for tree nurseries and apple orchards. Its causes are not fully understood up to now and economically feasible and sustainable countermeasures do not exist. Research studies to unravel the etiology of ARD are in urgent need of sites differing in soil characteristics with a defined, comparable cropping history including appropriate control (healthy) plots. Thus, the first aim of this study was to induce ARD at three different sites with topsoils covering textures from sand, loamy sand to silt loam (Podzols to Luvisols). Grass plots served as controls. After eight years of repeatedly replanting the apple rootstock ‘Bittenfelder’, growth suppression was observed at the ARD plots on all three sites. Because until now no systematic correlation to soil parameters was approached, the second aim was to study the replant severity in the three different soils. Soil properties were investigated at different spatial scales. Significant differences occurred between sites in soil texture, pH, and C and N contents. Within plots, non-invasive soil sensing (EMI, gamma-spectrometry) helped to ensure homogeneous conditions and to exclude unexplained ARD effects due to small-scale soil heterogeneity. Soil from each site was submitted to a bio-test in which growth of in vitro propagated M26 plantlets in untreated and disinfected soil was compared to determine the ARD severity. Soil disinfection by gamma irradiation resulted in a significant increase in M26 shoot biomass, most pronounced in soil from ARD plots. Thus, on all soils, ARD was successfully induced with a negative correlation between ARD intensity and soil clay content, and a positive correlation with C/N ratio.

Study on the Productivity of Grass Forage as a Feed Source for Sambar Deer (Cervus unicolor) in Deer Captivity of PT. Gunung Madu Plantations

Sambar deer (Cervus unicolor) is one of the protected animals. However now the existence of sambar deer is increasingly threatened. Therefore, there is need for ex-situ conservation activities, one of the mis deer captivity in PT. Gunung Madu Plantations. An important component in the management of wildlife in captivity is the availability of food plants that need to be observed that aims to determine the productivity of forage as feed for sambar deer. The research method used a castle method by making the sample plots of grass. The results showed that there are two types of grass that feed the sambar deer in captivity. This type of feed consists pait grass (Axonopus compressus) and elephant grass (Pennnisetum purpureum). Pait grass (Axonopus compressus) has a productivity of 10,02 kg/m2/day, larger than the elephant grass (Pennnisetum purpureum) with a productivity of 3,94 kg/m2/day. Keywords: Cervus unicolor, grass, productivity of grass forage, PT. Gunung Madu Plantations.

Drawbar Parameters of Tractor with Prototypes of Driving Wheels and Standard Tyres

Abstract The paper presents the main drawbar parameters of tractor (drawbar pull, drawbar power and wheels slip) operating in a grass plot and evaluates the utilization of specially modified tyres with spikes. These prototypes of driving wheels were designed at the Department of Transport and Handling of the Slovak University of Agriculture in Nitra. The designed mechanism with spikes is mounted on standard tractor tyres, in which grooves were made. Spikes are hidden in grooves during transportation on a route. On the grassy landscape or soil, the spikes are ejected in order to improve the drawbar parameters. During operation, the drawbar pull and the rotation speeds of wheels were measured, whereupon the wheel slip was calculated. Results show the highest increase in tractor speed at the second gear and high load in utilized prototypes of the driving wheels (1.89 km·h-1) in comparison to standard tyres (1.10 km·h-1). Measurements also demonstrate the highest improvement of drawbar power under the aforementioned conditions in case of tractor with prototypes of driving wheels (1,719.87 W) in comparison with tractor using the standard tyres (1,061.57 W).

Economic Competitiveness of Napier Grass in Irrigated and Non-irrigated Georgia Coastal Plain Cropping Systems

Interest and focus on development of renewable biofuels has been increasing over the past decade leading to the introduction of a wide cadre of renewable feedstocks. As a result, numerous perennial warm-season grasses have been introduced and management practices evaluated to determine their suitability as biofuel feedstocks. “Merkeron” napier grass (Pennisetum purpureum) plots were established in 2010 and harvested during crop years 2011 through 2015 adjacent to an on-going peanut (Arachis hypogaea L.), corn (Zea mays L.), and cotton (Gossypium hirsutum L.) cropping systems study conducted at the USDA/ARS Multi-crop Irrigation Research Farm in Shellman, GA (84 36 W, 30 44 N) on a Greenville fine sandy loam (fine, kaolinitic, thermic Rhodic Kandiudults). Napier grass was produced in both non-irrigated and two irrigated levels with different levels of nitrogen and potassium fertilizers. Peanut, corn, and cotton were produced in non-irrigated and full irrigation regimes. Breakeven prices for napier grass ranged from $65 to $84 Mg−1 at variable and total costs. The breakeven napier grass price was estimated such that the net returns were equal between napier grass and peanut, cotton, corn cropping systems. At variable production cost, comparative breakeven napier grass prices for non-irrigated, 50% irrigated, and full irrigated regimes were $77, $117, and $112 Mg−1, respectively. Napier grass did not compete economically against traditional irrigated cropping systems. Depending on traditional crop prices and bioenergy feed stock prices, napier grass could offer economic opportunities in non-irrigated production environments, riparian buffer zone edges, or non-cropped marginal production areas.

Estado físico-químico del suelo en pasturas con y sin maní forrajero (Arachis pintoi), URACCAN -Siuna

El estudio fue desarrollado en un área de una manzana, propiedad del señor Marvin Calderón, localizada en la comunidad Yaoya, municipio de Siuna. El objetivo fue comparar el estado físico–químico del suelo en pasturas con y sin maní forrajero (Arachis pintoi). Es cuasi experimental pre test, post test, longitudinal y descriptivo y se utilizó la técnica observacional. Se concluye, que el Arachis pintoi es una especie que contribuye al mejoramiento de la calidad del suelo y se recomienda el uso de prácticas agronómicas antes y después de establecer el mismo. El establecimiento del Arachis pintoi y la parcela de pasto sin este, cuestan en total C$ 7,377. 00.

Application of SWAT99.2 to sensitivity analysis of water balance components in unique plots in a hilly region

Although many sensitivity analyses using the soil and water assessment tool (SWAT) in a complex watershed have been conducted, little attention has been paid to the application potential of the model in unique plots. In addition, sensitivity analysis of percolation and evapotranspiration with SWAT has seldom been undertaken. In this study, SWAT99.2 was calibrated to simulate water balance components for unique plots in Southern China from 2000 to 2001, which included surface runoff, percolation, and evapotranspiration. Twenty-one parameters classified into four categories, including meteorological conditions, topographical characteristics, soil properties, and vegetation attributes, were used for sensitivity analysis through one-at-a-time (OAT) sampling to identify the factor that contributed most to the variance in water balance components. The results were shown to be different for different plots, with parameter sensitivity indices and ranks varying for different water balance components. Water balance components in the broad-leaved forest and natural grass plots were most sensitive to meteorological conditions, less sensitive to vegetation attributes and soil properties, and least sensitive to topographical characteristics. Compared to those in the natural grass plot, water balance components in the broad-leaved forest plot demonstrated higher sensitivity to the maximum stomatal conductance (GSI) and maximum leaf area index (BLAI).

Examination of the Potential of Terrestrial Laser Scanning and Structure-from-Motion Photogrammetry for Rapid Nondestructive Field Measurement of Grass Biomass

Above ground biomass (AGB) is a parameter commonly used for assessment of grassland systems. Destructive AGB measurements, although accurate, are time consuming and are not easily undertaken on a repeat basis or over large areas. Structure-from-Motion (SfM) photogrammetry and Terrestrial Laser Scanning (TLS) are two technologies that have the potential to yield precise 3D structural measurements of vegetation quite rapidly. Recent advances have led to the successful application of TLS and SfM in woody biomass estimation, but application in natural grassland systems remains largely untested. The potential of these techniques for AGB estimation is examined considering 11 grass plots with a range of biomass in South Dakota, USA. Volume metrics extracted from the TLS and SfM 3D point clouds, and also conventional disc pasture meter settling heights, were compared to destructively harvested AGB total (grass and litter) and AGB grass plot measurements. Although the disc pasture meter was the most rapid method, it was less effective in AGB estimation (AGBgrass r2 = 0.42, AGBtotal r2 = 0.32) than the TLS (AGBgrass r2 = 0.46, AGBtotal r2 = 0.57) or SfM (AGBgrass r2 = 0.54, AGBtotal r2 = 0.72) which both demonstrated their utility for rapid AGB estimation of grass systems.

Ground cover and slope exposure effects on micro- and mesobiota in forest soils

The interrelation of Alpine topography with the micro − and mesobiota is still poorly understood. We investigated the effects of ground cover type and slope exposure on the soil microbial biomass (double-stranded DNA, dsDNA) and abundances (real time PCR, qPCR); hydrolytic enzyme activities; and enchytraeid community structure in top soils (2.5-cm increments depth) in subalpine forests in the Italian Alps. Dominant ground covers were grass, moss, litter and woody debris at the north- and the south-facing slopes. The autochthonous soil microbiota (bacteria, fungi and archaea) was quantified by qPCR in the extracellular (eDNA) and intracellular fraction (iDNA) of the total soil DNA pool. A higher eDNA/iDNA ratio indicative of lower microbial activity was recorded in the deepest layer of the grass plots at the north-facing slope. This can be related to a lower degradation of eDNA and/or to an accumulation of eDNA with increasing depth as a result of leaching. The exposure effect was enzyme-specific and higher activities occurred under woody debris primarily at the south-facing slope. These plots also showed a higher nutrient content and a greater microbial biomass assessed as dsDNA yields. Total microannelid abundance was elevated on north-facing slopes on account of strong acidity indicator species. This was related to soil pH being one unit lower compared to the south-facing slope. The thickness of the organic layer (OL+OF+OH) was elevated at the north-facing slope due to a considerably thicker OH-horizon. The vast majority of microannelids at this slope occurred in the organic layer, while at south exposure they were almost evenly distributed between the organic layer and the mineral soil (A-horizon). Exposure was found to be more determinative for the composition of microannelid assemblages than the ground cover type.

The Effect of Floristic Composition on Bird Communities in a Set of Four Grassland Reconstruction Types

With most native prairie now lost, focus has turned to reconstructing grasslands with the aim of replicating ecosystem function for grassland fauna and flora. We report the results of a seven-year study (2008–2014) on the use of four floristically different prairie reconstructions by grassland birds. The study was conducted near Austin, Minnesota on a 64.75-ha (160-acre) Wildlife Management Area. Prairie reconstruction was implemented in 2005 on land previously used for row crops, and the study site consisted of eight identically sized (4.5 hectare), side-by-side of replicates of four distinct planting mixes. We used fixed-point transect surveys to document differences in the number of species and individuals of grassland birds between plot types. We found differences in the abundance of individuals and diversity of bird species between plot types, with fewer bird species and individuals present in lower plant-diversity plot types compared to higher plant-diversity plots. Eighteen species of grassland birds were recorded on the site, with none exclusively restricted to any plot type. Grassland obligate bird species, including Sturnella magna (Eastern Meadowlark), Dolichonyx oryzivorus (Bobolink), Ammodramus savannarum (Grasshopper Sparrow), Ammodramus henslowii (Henslow's Sparrow), and Passer-culus sandwichensis (Savannah Sparrow), were documented using low floristic diversity, cool-season grass plots. Other species, such as Spiza americana (Dickcissel), Melospiza melodia (Song Sparrow) and Spinus tristis (American Goldfinch), showed preferences for high diversity, forb dominated plots. Our results indicate that planting a mosaic of restoration mixes may be the most successful at attracting and retaining the highest diversity of bird species.

Comparison of 16 models for reference crop evapotranspiration against weighing lysimeter measurement

Accurate estimation of reference crop evapotranspiration (ET0) is important due to its crucial role in determining crop water requirement in irrigated agriculture. Though a great number of models have been developed, their rigorous evaluation with measurements is still lacking, leading to confusion and arbitrariness in model selection. In this paper daily estimates of 16 ET0 models, including five combination-, six radiation and five temperature-based ones, were compared with weighing lysimeter measurements during crop growing season (April through October) in 2012 at a semiarid site in China. Daily ET0 was measured by two weighing lysimeters (area 1.3m×1.3m, depth 2.3m) located in a fescue grass (Festuca arundinacea Schreb) plot (100m×100m) surrounded by a 167ha crop, winter wheat rotated with summer maize. We found the models were ranked decreasingly as: FAO-ppp-17 Penman>1963 Penman>FAO-24 Blaney-Criddle (BC)>1996 Kimberly Penman>FAO-24 radiation>FAO-56 Penman-Monteith (PM)>FAO-24 Penman>Turc>DeBruin-Keijman>Jensen-Haise>Priestley-Taylor>Hargreaves>Makkink>Hamon>Blaney- Criddle>Mcloud on basis of RMSE (root mean square error). Overall, the combination models performed best with RMSE ranging from 0.93 to 1.32mmd−1, followed by the radiation models with RMSE from 1.28 to 1.79mmd−1, and the temperature models with RMSE from 1.09 to 2.48mmd−1. The best combination model (FAO-ppp-17 Penman) was respectively 29% and 17% more accurate than the best radiation (FAO-24 radiation) and temperature (FAO-24 BC) models. Better performance of the combination and radiation models resulted because they explicitly contain the dominant factors influencing ET0. All models tended to overestimate under low evaporative demand while underestimating the measured values under high demand, but on average the combination and radiation methods underestimated by 0.46mmd−1 and 0.60mmd−1, respectively, whereas the temperature method overestimated by 0.21mmd−1. All combination and radiation models, and the Hargreaves and FAO-24 BC in temperature method showed robust structure. To improve them future efforts should be on local calibration, but for temperature models showing structure failure focus should be on its optimization. The coefficients of commonly used models were calibrated and related to meteorological variables. Particularly, those of the Priestley-Taylor, Makkink, Turc and the Hamon were enhanced, while those of the Hargreaves and BC were decreased. In climate similar to the current site in China we suggest continued use of the older Penman equations for combination method and the FAO-24 radiation or Turc for radiation method. Meanwhile, two questions need to be addressed in future studies: i) adoption of the FAO-56 PM equation as the sole standard for computing ET0 and the proper value for surface resistance; and ii) the effectiveness of the later modifications to the original wind function in the Penman equation.

Plasticity in turtle grass (Thalassia testudinum) flower production as a response to porewater nitrogen availability

Terrestrial plants often demonstrate plasticity in reproductive timing and output in response to environmental conditions such as temperature, photoperiod, water availability and nutrients. Despite the importance of sexual reproduction for seagrass establishment and persistence, factors influencing reproductive timing and output of these underwater marine plants remain largely unknown. We used a manipulative field-based experiment to assess the effect of porewater nitrogen on turtle grass (Thalassia testudinum) flower production. Experiments were conducted within monospecific turtle grass beds in Lower Laguna Madre, Texas, a region with consistently low water column and porewater nutrient levels. We enriched 50 turtle grass plots with fertilizer buried within the sediment at the rhizome layer. This resulted in increased porewater ammonium concentrations of 679±188μM in enriched plots, compared to 204±34μM in unenriched plots. After the onset of the reproductive season, we examined turtle grass reproductive status, plant morphology and elemental composition. Unenriched plots had a higher proportion of reproductive shoots (0.19±0.10) than enriched (0.08±0.04) plots. Shoots from enriched plots, alternatively, assimilated additional available nitrogen into leaf tissue and had more leaves that were longer and wider than their unenriched counterparts. Our results indicate that turtle grass exhibits plasticity in reproduction as a response to nutrient availability, whereby under low porewater nitrogen conditions, resources are diverted to sexual reproduction rather than somatic growth. The worldwide increase in coastal nutrient loading, particularly in the form of submarine groundwater discharge, has the potential to reduce flowering in Thalassia species.

Effects of vineyard floor cover crops on grapevine vigor, yield, and fruit quality, and the development of the vine mealybug under a Mediterranean climate

The influence of complete cover cropping (inter- and intra-row) on grapevine growth, yield and must quality was evaluated in a three-year field trial in a commercial vineyard in northwestern Sardinia (Italy). Effects on developmental and reproductive parameters of the vine mealybug, Planococcus ficus (Signoret) (Hemiptera: Pseudococcidae), were also investigated. The cover crop treatments were: natural covering, legume mixture, grass mixture, and conventional soil tillage, which was included as the reference treatment. Relative to soil tillage, cover crops reduced grape production by modifying yield components in different ways: legume mixture reduced the cluster weight, whereas grass mixture led to a lower number of clusters per vine coupled with a lower cluster weight. Cover crops also altered the must qualities relative to soil tillage. Grass mixture increased the content of sugar, anthocyanins and polyphenols, whereas legume mixture and natural covering reduced total polyphenols and anthocyanin content, respectively. All the P. ficus biological parameters examined were affected by the floor management practices. Mealybugs reared on grapevines subjected to soil tillage and legume covering showed a faster development time and higher survival, fecundity and fertility than those developed on natural covering and grass plots. The vine mealybug showed a higher performance on grapevines with a higher nitrogen content and vigor. Effects of cover crop treatments appear to be mediated through nutrient availability and content in grape plants. Consequently, utilizing competitive cover crops, while reducing yields, would improve must quality and reduce pest development.

Soil Phosphorus Remediation by Bahia Grass, Common Bermuda Grass, Crab Grass, and Switch Grass

ABSTRACTSoil phosphorus (P) removal by harvest may be a practical remediation strategy. Small plots of bahia grass (BG) (Paspalum notatum Flügge), common bermuda grass (CB) (Cynodon dactylon (L.) Pers.), crab grass (CG) (Digitaria ciliaris (Retz.) Koel.), and switch grass (SG) (Panicum virgatum L.) were established on a coastal plain soil (Mehlich 3P, 100–500+ mg kg−1) . Yield, tissue P concentration, and uptake P were determined in 2002–2005, and surface (0–15 cm) soil P were determined in 2002 and 2005. The uptake decreased, SG > CG > BG = CB (range 230–90 kg ha−1), paralleling the decrease in surface soil P. Uptake depended on soil P (P < 0.01–0.10), with uptake > surface soil P decrease at low soil P due to uptake from subsoil but decrease > uptake at high soil P due to leaching. Soil P concentration did not affect SG tissue P nor did multiple harvests decrease its relative productivity.