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PubMed2006

Interpretation of California mastitis test scores using Staphylococcus aureus culture results for screening of subclinical mastitis in low yielding smallholder dairy cows in the Dar es Salaam region of Tanzania.

Screening of subclinical mastitis under field conditions is done using the California mastitis test (CMT). CMT score of > or = 1 corresponding to > or = 500,000 somatic cells ml(-1) is commonly used as threshold of subclinical mastitis in temperate countries. However, given the innately high physiological level of somatic cells in low yielding dairy cows, this threshold may not apply to low yielding dairy cows. The current study was undertaken to investigate the clinical utility of CMT for screening of Staphylococcus aureus subclinical mastitis in low yielding smallholder dairy cows in Tanzania. A total of 1151 of quarter-milk samples were CMT tested, of these 914-originated from cows with a lactation period of 14-305 days. All samples were screened for subclinical mastitis by the CMT as well as microbiological culture of single, duplicate (two consecutive) and triplicate (three consecutive) samples as a gold standard. For the duplicate and triplicate quarter-samples, cows were considered positive for S. aureus subclinical mastitis if results of microbiologic culture for S. aureus were positive for two of two, and for at least two of the first three consecutive quarter-milk samples collected from that cow, respectively. Using a CMT score of > or = 1 would classify 78.6% of the 940 quarter-samples as positive. Eighty-two percent of the samples in which S. aureus was isolated had CMT scores > or = 2; this would classify 51.6% of the 940 quarter-samples as positive. For the single sample, this cut-off had sensitivity, specificity and likelihood ratio for S. aureus of 0.87, 0.83 and 4.24, respectively. For the duplicate quarter-milk samples this cut-off had sensitivity, specificity, and likelihood ratio of 0.94, 0.86, and 5.19. While, for the triplicate quarter-milk samples this cut-off had sensitivity, specificity and likelihood ratio of 0.97, 0.92 and 7.47, respectively. Based on these results and practical considerations, it is concluded that CMT score of > or = 2 corresponding to > or = 800,000 somatic cells Ml(-1) is the best cut-off to correctly identify S. aureus intramammary infections in low yielding dairy cows in Tanzania.

Animals↗

PubMed2005

Effects of exogenous progesterone on gestation length, foetal survival and colostrum yield in ewes.

Twin bearing mature ewes (n=40) were treated with exogenous progesterone (100mg daily in oil) or vehicle (oil control) from Day 143 of gestation until lambing to investigate the effects on gestation length, foetal survival and colostrum yield and composition. Compared to control ewes, progesterone treated ewes had increased (P<0.05) serum progesterone concentrations (by 4.3 ng/ml) before lambing and in the first day post-partum (by 10 ng/ml). Progesterone treatment increased gestation length (150.4+/-0.6 days versus 147.8+/-0.6 days, P<0.05) and colostrum yield at 1h after lambing (P<0.05) but the colostrum had a lower concentration of IgG (P=0.02). In the first 24h after lambing, total colostrum and IgG yields were not different between groups. Four (20%) of the progesterone treated ewes produced either one or two dead lambs, while one ewe died on day 155 without initiating the birth process. We conclude that the daily administration of 100mg progesterone resulted in extended gestation length and reduced lamb survival but did not lower colostrum yield.

Animals↗

PubMed2006

P13 of Leucania separata multiple nuclear polyhedrosis virus affected the polyhedra and budded virions yields of AcMNPV.

p13 gene was first described by our laboratory in Leucania separata multiple nuclear polyhedrovirus (Ls-p13, ORF114) back to 1995. However, the functions of Ls-P13 and its reported homologues remained unknown. In order to probe the function of Ls-P13, recombinant Autographa californica nucleopolyhedroviruses (rAcMNPVs) were constructed to express Ls-P13 in the Sf9 cells at early, late or early/late phase. Observations of microscope showed that the expression of Ls-P13 could decrease the yield of AcMNPV polyhedra in Sf9 cells, and early expressed Ls-P13 had stronger inhibition efficiency than that of the late expressed. Results of flow cytometry also indicated that Ls-P13 decreased the yield of AcMNPV polyhedra while increased those of budded virions (BVs) in Sf9 cells, but the efficacy was lost when its leucine zipper-like domain was mutated. Ls-P13 is a transmembrane protein, which was early located in the nucleus and late mainly in the cytoplasm membrane at 48 h. When its transmembrane domains were deleted, Ls-P13 distribution was dramatically diverted from cytoplasm membrane to nucleus, its corresponding efficacy on polyhedra yield was further increased while that on BVs was slightly weakened. Bioassay results indicated that Ls-P13 accelerated the larvae-killing rate. The mechanism might be that Ls-P13 increased BV yield.

Animals↗

PubMed2006

Methane yield in source-sorted organic fraction of municipal solid waste.

Treating the source-separated organic fraction of municipal solid waste (SS-OFMSW) by anaerobic digestion is considered by many municipalities in Europe as an environmentally friendly means of treating organic waste and simultaneously producing methane gas. Methane yield can be used as a parameter for evaluation of the many different systems that exist for sorting and pre-treating waste. Methane yield from the thermophilic pilot scale digestion of 17 types of domestically SS-OFMSW originating from seven full-scale sorting systems was found. The samples were collected during 1 year using worked-out procedures tested statistically to ensure representative samples. Each waste type was identified by its origin and by pre-sorting, collection and pre-treatment methods. In addition to the pilot scale digestion, all samples were examined by chemical analyses and methane potential measurements. A VS-degradation rate of around 80% and a methane yield of 300-400Nm(3) CH(4)/ton VS(in) were achieved with a retention time of 15 days, corresponding to approximately 70% of the methane potential. The different waste samples gave minor variation in chemical composition and thus also in methane yield and methane potential. This indicates that sorting and collection systems in the present study do not significantly affect the amount of methane produced per VS treated.

Environmental Pollutants↗

PubMed2026

Whole-Exome Sequencing in a Consanguinity-Enriched South Indian Retinitis Pigmentosa Cohort: Diagnostic Yield and Molecular Spectrum.

PURPOSE: To determine the molecular diagnostic yield, variant spectrum, inheritance architecture, and influence of consanguinity on whole-exome sequencing outcomes in a South Indian retinitis pigmentosa (RP) cohort. DESIGN: Prospective, registry-based cohort study. SUBJECTS: A total of 113 affected participants were enrolled through the Aravind Registry for Inherited Diseases of the Eye, including 109 unrelated probands and 4 affected relatives from already represented families. Primary analyses were restricted to the 109 unrelated probands. METHODS: Whole-exome sequencing was performed using a clinical exome workflow. Variants were interpreted using American College of Medical Genetics and Genomics/Association for Molecular Pathology criteria and cases were categorized as solved, possibly solved, inconclusive, or unsolved using prespecified inheritance-aware rules. MAIN OUTCOME MEASURES: Molecular diagnostic yield, distribution of implicated genes and variant classes, inheritance architecture, and diagnostic yield stratified by consanguinity status. RESULTS: Among the 109 unrelated probands, mean age at testing was 39.3 ± 14.1 years and 58.7% were male. Whole-exome sequencing identified 186 distinct rare variants across 92 inherited retinal disease genes, including 26 pathogenic and 33 likely pathogenic variants. A molecular diagnosis was established in 50 of 109 probands (45.9%), including 42 solved and 8 possibly solved cases; 45 (41.3%) were inconclusive and 14 (12.8%) remained unsolved, including 4 (3.7%) in whom no candidate variant was identified. EYS, USH2A, and ADGRV1 were the most frequently implicated genes. Autosomal recessive (AR) disease predominated (44/50, 88.0%). Consanguineous AR cases were exclusively homozygous (17/17); notably, 68.0% of nonconsanguineous AR cases were also homozygous (P = 0.013). Diagnostic yield was higher in consanguineous probands (51.4% vs. 41.7%), without reaching significance. Recurrent alleles included an established South Asian founder variant (MFSD8 c.1361T>C) and candidate founder alleles in EYS (c.4321C>T) and ADGRV1 (c.14329C>T). CONCLUSIONS: Whole-exome sequencing established a molecular diagnosis in nearly half of this South Indian RP cohort and revealed a predominantly recessive, homozygosity-enriched architecture shaped by consanguinity. These findings define a region-specific variant landscape to support clinical interpretation, genetic counseling, and future trial enrollment in this underrepresented population. FINANCIAL DISCLOSURES: The authors have no proprietary or commercial interest in any materials discussed in this article.

Consanguinity↗

PubMed2000

Decay kinetics and quantum yields of fluorescence in photosystem I from Synechococcus elongatus with P700 in the reduced and oxidized state: are the kinetics of excited state decay trap-limited or transfer-limited?

Transfer and trapping of excitation energy in photosystem I (PS I) trimers isolated from Synechococcus elongatus have been studied by an approach combining fluorescence induction experiments with picosecond time-resolved fluorescence measurements, both at room temperature (RT) and at low temperature (5 K). Special attention was paid to the influence of the oxidation state of the primary electron donor P700. A fluorescence induction effect has been observed, showing a approximately 12% increase in fluorescence quantum yield upon P700 oxidation at RT, whereas at temperatures below 160 K oxidation of P700 leads to a decrease in fluorescence quantum yield ( approximately 50% at 5 K). The fluorescence quantum yield for open PS I (with P700 reduced) at 5 K is increased by approximately 20-fold and that for closed PS I (with P700 oxidized) is increased by approximately 10-fold, as compared to RT. Picosecond fluorescence decay kinetics at RT reveal a difference in lifetime of the main decay component: 34 +/- 1 ps for open PS I and 37 +/- 1 ps for closed PS I. At 5 K the fluorescence yield is mainly associated with long-lived components (lifetimes of 401 ps and 1.5 ns in closed PS I and of 377 ps, 1.3 ns, and 4.1 ns in samples containing approximately 50% open and 50% closed PS I). The spectra associated with energy transfer and the steady-state emission spectra suggest that the excitation energy is not completely thermally equilibrated over the core-antenna-RC complex before being trapped. Structure-based modeling indicates that the so-called red antenna pigments (A708 and A720, i.e., those with absorption maxima at 708 nm and 720 nm, respectively) play a decisive role in the observed fluorescence kinetics. The A720 are preferentially located at the periphery of the PS I core-antenna-RC complex; the A708 must essentially connect the A720 to the reaction center. The excited-state decay kinetics turn out to be neither purely trap limited nor purely transfer (to the trap) limited, but seem to be rather balanced.

Chlorophyll↗

PubMed1974

Photoelectron quantum yields of hemin, hemoglobin, and apohemoglobin. Possible applications to photoelectron microscopy of heme proteins in biological membranes.

Hemoglobin is examined as a model system for intrinsic photoelectron labeling experiments. The absolute photoelectron quantum yields of hemin, hemoglobin, and apohemoglobin thin films were measured in the 180-230 nm wavelength region. Hemin exhibits a quantum yield of approximately 6 x 10(-4) electrons per incident photon at 180 nm, 9 x 10(-5) electrons per incident photon at 210 nm, and 2 x 10(-6) electrons per incident photon at 230 nm. At all wavelengths the hemin curve lies approximately a factor of 20 above that of hemoglobin and two orders of magnitude above that of apohemoglobin. High image contrast is observed between hemin and apohemoglobin in low magnification photoelectron micrographs, suggesting the feasibility of intrinsic labeling studies involving heme proteins. The quantum yield of hemoglobin is discussed in terms of linear contributions from heme groups and protein weighted by their relative surface areas. The fractional surface areas based on the known structure of hemoglobin are consistent with values derived from the quantum yields of hemin and apohemoglobin.

Animals↗

PubMed1987

A new method for measuring the yield stress in thin layers of sedimenting blood.

A new method is presented to describe the low shear rate behavior of blood. We observed the response of a thin layer of sedimenting blood to a graded shear stress in a wedge-shaped chamber. The method allows quantitation of the degree of phase separation between red cells and plasma, and extracts the yield stress of the cell phase as a function of hematocrit. Our studies showed that the behavior of normal human blood underwent a transition from a solid-like gel to a Casson fluid. This transition began at the Casson predicted yield stress. The viscoelastic properties of blood were examined at shear stresses below the yield stress. The measured Young's elastic moduli were in good agreement with published data. The yield stress of blood showed a linear dependence on hematocrit up to 60%, and increased more rapidly at higher hematocrit.

Blood Sedimentation↗

PubMed2003

[Complications and yield of percutaneous liver biopsy with ultrasonographic marking].

OBJECTIVES: To describe the complications and the diagnostic yield of percutaneous liver biopsies performed under ultrasonographic control in an Internal Medicine department. PATIENTS AND METHODS: A total of 750 percutaneous liver biopsies were performed at the Internal Medicine department of our institution during the 1995-2001 time period. The Menghini technique was employed previous ultrasonographic marking of the puncture site was performed by the same physicians who performed the biopsy. Major and minor complications as well as the diagnostic yield (obtention of diagnostic hepatic tissue) of the technique were recorded. RESULTS: No deaths occurred in our series. Two patients (0.3%) had major complications presenting as liver subcapsular hematoma with hemoperitoneum which resolved with conservative measures. One of them was a male patient with acute leukemia and the other was a woman on antiaggregant therapy. Eight patients (1.1%) had minor complications (vasovagal syncope), all of them young males. In three cases no adequate material for diagnosis was obtained (technique yield 99.6%). CONCLUSIONS: In our series, percutaneous liver biopsy with ultrasonographic marking is a diagnostic technique associated with a low rate of severe complications and with a high diagnostic yield. The use of ultrasonographic marking by the same physicians performed the biopsy does not involve a longer time or increased cost of the technique, provides more safety in the procedure and has a low morbidity rate. This procedure could be used on a routine basis for all percutaneous liver biopsies.

Adolescent↗

PubMed2004

A prospective comparison of the yield of EUS in primary vs. recurrent idiopathic acute pancreatitis.

BACKGROUND: It is uncertain whether EUS should be performed after a single episode of idiopathic pancreatitis vs. recurrent episodes or if clinical factors can predict positive EUS findings. METHODS: Consecutive patients with a single episode of idiopathic pancreatitis or with recurrent episodes underwent EUS (with analysis of bile for bilirubinate and cholesterol crystals, when possible). The diagnostic yield was compared for patients with a single episode of idiopathic pancreatitis and recurrent episodes (stratified by cholecystectomy status). Predictors of positive EUS findings were sought. EUS was considered "positive" if it identified any possible cause of pancreatitis other than chronic pancreatitis. RESULTS: A total of 370 patients were studied (246 no-cholecystectomy group [134 single episode of idiopathic pancreatitis, 112 recurrent episodes] and 124 post-cholecystectomy group [67 single episode of idiopathic pancreatitis, 57 recurrent episodes]). Overall, EUS yielded a positive finding in 29.2%. For patients in the no-cholecystectomy group, positive EUS findings were not significantly more frequent in those with a single episode of idiopathic pancreatitis vs. those with recurrent episodes (31.3% vs. 32.1%; p = 0.89). In the post-cholecystectomy group, the yield was not significantly different for single episode of idiopathic pancreatitis (29.9%) vs. recurrent episodes (17.5%) ( p = 0.15). Chronic pancreatitis was the only abnormality identified in 30.9% of patients in the no-cholecystectomy group vs. 26.6% of those in the post-cholecystectomy group ( p = 0.24). It was the most common abnormality found in all 4 subgroups (range 16.4%-42.0%) and was approximately twice as frequent in patients with recurrent episodes vs. a single episode of idiopathic pancreatitis (no-cholecystectomy: 42.0% vs. 21.6%, p = 0.0008; post-cholecystectomy: 38.6% vs. 16.4%, p = 0.008). Analysis of bile revealed crystals in 38/80 (47.5%) patients in whom it could be performed. Patients with positive EUS findings tended to be older. CONCLUSIONS: In patients with idiopathic pancreatitis, the yield of EUS is not significantly different after an initial attack or after recurrent attacks. Therefore, it is reasonable to perform EUS after an initial attack of idiopathic acute pancreatitis, especially in older patients.

Acute Disease↗

PubMed2003

A rate-dependent microcrack-bridging model that can explain the strain rate dependency of cortical bone apparent yield strength.

Although there are empirical correlations between strain rate, cortical and cancellous bone apparent stiffness, apparent yield strength, apparent ultimate strength and cortical bone fracture toughness, a mechanistic description for these phenomena is lacking. Microcracking is a major mechanism in cortical and cancellous bone failure, however, microdamage content alone cannot explain the strain rate dependence of bone strength without considering time-dependent behavior of the crack. Using a rate-dependent model of a fiber-bridged microcrack and data from the literature, we demonstrate that the experimental apparent yield strength of bone can be predicted directly from measurements of apparent moduli of elasticity of bone constituents and failure strain of the collagenous matrix. Yield strength predictions for estrogen depleted bone were made using the model and data from ovariectomized sheep. It was predicted that the yield strength of estrogen-deficient bone is comparable to that of normal bone within strain rates associated with physiological activities. For high strain rates, however, the strength of estrogen-depleted bone was predicted to be much weaker than normals suggesting a higher fracture risk due to impact from falls, for individuals with estrogen-depleted bones such as in post-menopausal osteoporosis.

Bone and Bones↗

PubMed1999

The role of the lamellar interface during torsional yielding of human cortical bone.

Fragility fractures are a result of alterations in bone quantity, tissue properties, applied loads, or a combination of these factors. The current study addresses the contribution of cortical bone tissue properties to skeletal fragility by characterizing the shear damage accumulation processes which occur during torsional yielding in normal bone. Samples of human femoral cortical bone were loaded in torsion and damaged at a post-yield twist level. The number of microcracks within osteons, interstitial tissue, and along cement lines were assessed using basic fuchsin staining. Damage density measures (number of cracks/mm2) were correlated with stiffness degradation and changes in relaxation. Damaged samples exhibited a wide variation in total microcrack density, ranging from 1.1 to 43.3 cracks/mm2 with a mean density of 19.7 +/- 9.8 cracks/mm2. Lamellar interface cracks comprised more than 75% of the total damage, indicating that the lamellar interface is weak in shear and is a principal site of shear damage accumulation. Damage density was positively correlated with secant stiffness degradation, but only explained 22% of the variability in degradation. In contrast, damage density was uncorrelated with the changes in relaxation, indicating that a simple crack counting measure such as microcrack density was not an appropriate measure of relaxation degradation. Finally, a nonuniform microcrack density distribution was observed, suggesting that internal shear stresses were redistributed within the torsion samples during post-yield loading. The results suggested that the lamellar interface in human cortical bone plays an important role in torsional yielding by keeping cracks physically isolated from each other and delaying microcrack coalescence in order to postpone the inevitable formation of the fatal crack.

Adult↗

PubMed1995

Diagnostic yield of the neurologic assessment of the developmentally delayed child.

OBJECTIVE: The aim of this study was to determine the etiologic yield of the neurologic assessment of a consecutive cohort of developmentally delayed children. STUDY DESIGN: A retrospective chart review was carried out on all patients referred to a single university-based pediatric neurologist for evaluation of global developmental delay from July 1991 to December 1993. Patients referred because of isolated speech or motor delay or autism or those who had been previously evaluated by another neurologist were excluded. RESULTS: A total of 77 patients were identified; 47 were male, and 62 were referred by a pediatrician. Neurologic evaluation did not confirm global delay in 10, and 8 did not complete diagnostic evaluation; one child was included in both groups. Of the remaining 60, an etiologic diagnosis was suspected by the referring physician at the time of referral in 13. Although parents suspected a delay at a mean age of 0.66 (+/- 0.69) year, children were examined by the neurologist at a mean age of 3.58 (+/- 2.42) years. Twenty-five were mildly delayed, 23 were moderately delayed, and 12 were severely delayed. Diagnostic studies (history, physical examination, and selected investigations, including screens for metabolic disease, karyotype, fragile X testing, electroencephalography, and neuroimaging) yielded an etiologic diagnosis in 38 (63.3%) of the 60 patients. Etiologic categories included cerebral dysgenesis (16.7%), hypoxic-ischemic encephalopathy (10.0%), chromosomal abnormalities (10%), toxins (8.3%), metabolic disorders (5.0%), and neurocutaneous (3.3%), neuromuscular (3.3%), genetic/dysmorphic (3.3%), and epileptic (3.3%) syndromes. Etiologic yield was equivalent across categories and degree of developmental delay. CONCLUSION: Referral to a pediatric neurologist and application of a selected battery of investigations yield etiologic findings with important implications with respect to management, prognosis, and recurrence risk estimate in a significant portion of globally delayed children.

Child, Preschool↗

PubMed2003

Multiple limit cycles in the chemostat with variable yield.

The global asymptotic behavior of solutions of the variable yield model is determined. The model generalizes the classical Monod model and it assumes that the yield is an increasing function of the nutrient concentration. In contrast to the Monod model, it is demonstrated that the variable yield model exhibits sustained oscillations. Moreover, it is shown that the variable yield model may undergo a subcritical Hopf bifurcation and feature at least two distinct limit cycles. Implications for the coexistence of competing populations are discussed.

Bacteria↗

PubMed1997

Venom yields from several species of colubrid snakes and differential effects of ketamine.

The composition of rear-fanged colubrid snake venoms is largely unknown due primarily to the difficulty involved in venom collection. Several different methods have been used to maximize the yield of Duvernoy's secretions. The method proposed by Rosenberg in 1992, which includes the use of ketamine hydrochloride anesthetic and pilocarpine to induce Duvernoy's glands secretion, was used in the present study to collect venom from eight species of colubrids. Protein concentrations, using a dye-binding microassay technique, were determined for the venoms collected. Average protein concentrations ranged from 49.8 to 96.4%. Most yields (dry weight/snake) obtained from specimens in this study were significantly greater than yields previously reported. There was a wide range of effects that occurred due to the ketamine injections; however, all snakes recovered from the effects of the ketamine hydrochloride/pilocarpine with no apparent ill effects. Recommended doses of ketamine hydrochloride have thus been adjusted, depending on previous reactions to the drug. The use of ketamine/pilocarpine in the collection of Duvernoy's secretion has proven to be highly effective in increasing yields. Some caution should be observed when administering ketamine to various species of colubrids, as effects do not necessarily scale to body mass.

Anesthetics, Dissociative↗

PubMed1997

2D motion aliasing yielding 3D ambiguity. A study with variants of a Necker cube.

The 2D projection of a rotating Necker cube yields an ambiguous 3D interpretation based on both 2D shape and kinetic depth information. The present study shows that the alternation rate of the two 3D interpretations is constant with the rotation speed up to some critical value (around 25 turns/min for a cube whose sides subtend 2.5 deg) and increases monotonically thereafter. It is proposed that the additional perceptual reversals (PRs) observed at high rotation speeds are due to the increased frequency of the crossovers of the cube's edges. These crossovers yield 2D motion "aliasing" (or discontinuity) and "veridical" (or continuity) motion components. The motion aliasing (or crossover) hypothesis states that, in addition to the inherent ambiguity of the dynamic 2D projection of 3D objects, perceptual motion/perspective reversals will occur any time the discontinuity speed takes over the continuity speed. It is proposed that the relative strengths of the two components depend on the linear speed of the projected edges and that the discontinuity components take over the continuity one in the speed range where contrast sensitivity (or, above threshold, efficiency) is a decreasing function of speed. The motion aliasing hypothesis was tested and supported in a series of independent experiments showing that, for rotation speeds higher than 25 turns/min the PR rate increases with the crossover frequency at a constant speed, with linear speed at a constant crossover frequency and with the similarity of the crossing bars in terms of their orientation, polarity and spatial overlap. In addition, some of these experiments suggest that 2D shape and kinetic depth 3D-cues combine in such a way that the average PR rate they yield together is the same as the PR rate yielded by each of them independently. In the Discussion section we elaborate on issues related to the perceptual combination of ambiguous shape and kinetic depth, 3D cues.

Depth Perception↗

PubMed2002

Methane yield as a monitoring parameter for the start-up of anaerobic fixed film reactors.

This paper describes the variation of the methane yield during the start-up period of an anaerobic fluidized bed reactor. After a lag phase, with acclimatized sludge, the methane yield increased with time during biofilm development up to the theoretical steady yield value, reported to be around 0.351 CH4/g CODdeg. The establishment of the biofilm required a high consumption of organic material through the microbial synthesis (anabolism), thereby reducing the proportion of substrate converted to methane. As a result, this yield could be an indirect metabolic parameter for evaluating a start-up operation. It could provide vital information about bacterial fixation processes and is easy to be applied to any biofilm reactor, such as anaerobic filters, where biomass sampling is impracticable. Monitoring this parameter could also give useful dynamic information about the different steps of colonization and biomass attachment, which could be used to improve the start-up performance.

Bacteria, Anaerobic↗

PubMed2001

Use of precision agriculture technology to investigate spatial variability in nitrogen yields in cut grassland.

Spatial variability in N uptake and utilisation by swards within uniformly managed field units could be responsible for a significant proportion of the NH3, N2O, NO3- and NOx (NO and NO2) 'pollutants' generated by agriculture and released to the environment. An investigation was commenced, therefore, to quantify, map and explain the spatial variability in sward N yield in a 'large' silage field and to assess the potential for managing this variability using some of the latest precision agriculture technology. Sward dry matter (DM) and N yields were predicted from the results of plant tissue analyses using mathematical models. Sward N yields were found to vary greatly across the field seemingly because of differences in net soil N mineralisation, but the pattern of variability appeared to remain constant with time. Conventional soil analysis of a range of soil chemical and physical properties, however, failed to explain this variability. It was concluded that the N-yield distribution map might be used in place of soil analysis as the basis for varying the rates of N application to different parts of the field with the twin objectives of maximising fertiliser use efficiency and minimising N emissions to air and water.

Agriculture↗