Pasture Phosphorus Research Articles

Reproductive performance of northern Australia beef herds. 5. Factors influencing risk of non-pregnancy

Context Sound reproductive efficiency is a key determinant for the overall productivity and profitability of a beef breeding business. Failure of a cow to conceive results in either culling or the cost of carrying non-pregnant animals. Aims This study aimed to determine and quantify the major factors associated with non-pregnancy in commercial beef breeding herds of northern Australia. Methods A prospective population-based epidemiological study of the likelihood of non-pregnancy in cows after an annual mating in northern Australian beef breeding cows used data from 73 herds from four broad country types and 62 323 animal years; approximately 80 property-, management-group- and cow-level risk factors were considered. A multivariable model building process was employed to scrutinise the resulting dataset, so as to identify what herd management practices, nutritional, environmental, and individual cow factors were associated with non-pregnancy and estimate their magnitude of effect. Key results Non-pregnancy was disproportionately high in the Northern Forest (32.1%), compared with the Northern Downs, Central Forest and Southern Forest where it was 17.1%, 16.0% and 13.2% respectively. Time of expected calving had the largest impact on occurrence of non-pregnancy. Parity also had a significant influence, with first-lactation cows typically having 5–12% higher non-pregnancy than did mature cows. Non-pregnancy decreased with an increasing body condition score at the branding/weaning muster for lactating cows. The difference in non-pregnancy when comparing availability of wet-season pasture phosphorus content and digestibility of pasture during the dry season was 13.2 and 10.2 percentage points respectively. Conclusions This study demonstrated the substantial impact environment, herd management practices, nutrition and disease factors can have on the reproductive performance of females. Implications To optimise the efficiency of females (through reducing the occurrence of non-pregnancy) under commercial conditions in northern Australia, production systems should support beef herds calving early in the production year, being in at least moderate body condition and having access to more digestible pastures that address the nutritional requirements for both protein and phosphorus. This indicates focus for management, especially in the Northern Forest where the likelihood of non-pregnancy was highest.

Grazing Management and Buffer Strips Impact Pasture Phosphorus Runoff

Grazing Management and Buffer Strips Impact Pasture Phosphorus Runoff

Validation of a quantitative phosphorus loss assessment tool.

Pasture Phosphorus Management Plus (PPM Plus) is a tool that allows nutrient management and conservation planners to evaluate phosphorus (P) loss from agricultural fields. This tool uses a modified version of the widely used Soil and Water Assessment Tool model with a vastly simplified interface. The development of PPM Plus has been fully described in previous publications; in this article we evaluate the accuracy of PPM Plus using 286 field-years of runoff, sediment, and P validation data from runoff studies at various locations in Oklahoma, Texas, Arkansas, and Georgia. Land uses include pasture, small grains, and row crops with rainfall ranging from 630 to 1390 mm yr, with and without animal manure application. PPM Plus explained 68% of the variability in total P loss, 56% of runoff, and 73% of the variability of sediment yield. An empirical model developed from these data using soil test P, total applied P, slope, and precipitation only accounted for 15% of the variability in total P loss, which implies that a process-based model is required to account for the diversity present in these data. PPM Plus is an easy-to-use conservation planning tool for P loss prediction, which, with modification, could be applicable at the regional and national scales.

Comparison of subsurface and surface runoff phosphorus transport rates in alluvial floodplains

Phosphorus (P) loading to streams can occur by both surface runoff and subsurface transport, with subsurface P transport often assumed negligible. Groundwater P concentrations in alluvial aquifers can be significant, especially in preferential flow paths (PFPs). The objectives of this research were to quantify subsurface P transport rates at two sites in northeastern Oklahoma and to compare them with surface runoff P transport rates derived from a hydrologic model, the Pasture Phosphorus Management Calculator (PPM Plus). Ozark ecoregion study sites were adjacent to the Barren Fork Creek and Honey Creek in northeastern OK, USA. Each site, instrumented with 24 observation wells, was monitored for several months for both groundwater levels and P concentrations. Using the flow and P concentration data, Monte Carlo simulations with Darcy's Law and a P transport rate equation were used to calculate the distributions of subsurface P transport rates across a transect within the well field containing a single identified PFP. Total subsurface P transport rates, through both the non-PFP flow domain and a single PFP, were estimated to be 0.04 kg year −1 and 0.03 kg year −1 for the Barren Fork Creek and Honey Creek field sites, respectively. Monte Carlo simulations for surface runoff P transport rates with PPM Plus resulted in average total P surface runoff transport rates of 0.07 kg year −1 for the Barren Fork Creek site and 0.08 kg year −1 for the Honey Creek site. For the groundwater at these floodplains, the P source was P-laden stream water flowing into the alluvial aquifer and a minimal quantity of P leaching from the surface. Results indicated that the subsurface P transport rates for small (3 ha) alluvial floodplain sites in the Ozark ecoregion were at least 0.03–0.04 kg year −1, although subsurface P transport rates may be higher in cases with greater numbers of PFPs and where the subsurface is connected to a larger P source.

A quantitative phosphorus loss assessment tool for agricultural fields

In the United States, government sponsored conservation programs are under increasing pressure to quantify the environmental benefits of practices they subsidize. To meet this objective, conservation planners need tools to accurately predict phosphorus (P) loss from agricultural lands. Existing P export coefficient based tools are easy to use, but do not adequately account for local conditions. Hydrologic and water quality models are more accurate, but are prohibitively complex for conservation planners to use. Pasture Phosphorus Management (PPM) Plus was developed as a user-friendly P and sediment loss prediction tool based on the Soil and Water Assessment Tool (SWAT), a popular comprehensive hydrologic and water quality model. PPM Plus is applicable under a wide variety of management options and conservation practices and simple enough for use by conservation planners. SWAT hydrologic components were calibrated to allow application anywhere in the State of Oklahoma. The SWAT model was modified to include soil P algorithm updates and improved representation of conservation practices. This tool was successfully validated using 286 field years of measured data from the southern United States. PPM Plus allows the development of more effective conservation plans by allowing planners to evaluate pollutant losses resulting from a particular management strategy prior to implementation.

Development of a Quantitative Pasture Phosphorus Management Tool Using the SWAT Model1

Abstract: Assessment tools to evaluate phosphorus loss from agricultural lands allow conservation planners to evaluate the impact of management decisions on water quality. Available tools to predict phosphorus loss from agricultural fields are either: (1) qualitative indices with limited applicability to address offsite water quality standards, or (2) models which are prohibitively complex for application by most conservation planners. The purpose of this research was to develop a simple interface for a comprehensive hydrologic/water quality model to allow its usage by farmers and conservation planners. The Pasture Phosphorus Management (PPM) Calculator was developed to predict average annual phosphorus (P) losses from pastures under a variety of field conditions and management options. PPM Calculator is a vastly simplified interface for the Soil and Water Assessment Tool (SWAT) model that requires no knowledge of SWAT by the user. PPM Calculator was validated using 33 months of data on four pasture fields in northwestern Arkansas. This tool has been extensively applied in the Lake Eucha/Spavinaw Basin in northeastern Oklahoma and northwestern Arkansas. PPM Calculator allows conservation planners to take advantage of the predictive capacity of a comprehensive hydrologic water quality model typically reserved for use by hydrologists and engineers. This research demonstrates the applicability of existing water quality models in the development of user friendly P management tools.

Assessing the bioavailability of dissolved organic phosphorus in pasture and cultivated soils treated with different rates of nitrogen fertiliser

A proportion of dissolved organic phosphorus (DOP) in soil leachates is readily available for uptake by aquatic organisms and, therefore, can represent a hazard to surface water quality. A study was conducted to characterise DOP in water extracts and soil P fractions of lysimeter soils (pasture before and after, and cultivated soil after leaching to simulate a wet winter–autumn) from a field trial. Data on DOP in drainage waters from the field trial were also generated. In water extracts, used as a surrogate for soil solution and drainage water, 70–90% of the total dissolved P (TDP) concentration was made up of DOP, of which 40% was hydrolysable by phosphatase enzymes. Proportions of hydrolysable DOP to TDP in drainage waters of the field trial were less than in water extracts due to enhanced DRP loss via dung inputs, but still large at 35% of DOP. Analysis of lysimeter soils by sequential fractionation indicated that several organic P fractions changed with land use and due to leaching. Further investigation using NaOH–EDTA extracts and 31P nuclear magnetic resonance spectroscopy indicated that the greatest changes were a decrease in the concentrations of orthophosphate diester P and an increase in orthophosphate monoester P. This was attributed to mineralization by cultivation and plant roots and also to the leaching of mobile diester P. This study suggests that in such soils with a dynamic soil organic P pool, the concentration of readily bioavailable P in soil solution and drainage waters and the potential to impair surface water quality cannot be determined from the DRP concentration alone.

A survey of the phosphorus and calcium contents of pastures and the serum inorganic phosphorus and calcium contents of cows on four Manawatu dairy farms

Serum inorganic phosphorus (Pi) and calcium (Ca) concentrations were assessed in 20 cows on each of four Manawatu factory supply dairy farms. Blood was taken from each cow before calving and at six-week intervals during lactation. Bleeding coincided with herd testing. Herds of Friesian or Friesian X cows and Jersey or Jersey X cows were compared on adjacent farms on a Central Yellow-brown Sand and on adjacent farms on a Peat Loam overlying a Central Yellow-brown Earth soil. Pasture mass and composition were estimated to grazing height in the next two paddocks to be grazed in the rotation. Mean serum Pi concentration was higher in cows on sandy soils (1.55 mmol Pi/l than in cows on the peat loam (1.34 mmol Pi/l (P<0.001). Concentrations were highest before calving (1.69 mmol Pi/l) but fell to low levels at peak lactation (1.17mmol Pi/l when 70% of cows were below the minima of the 'normal range', and during the drought (1.29 mmol Pi/l. Pasture phosphorus (P) concentrations were adequate to support cow nutrition for lactation (>0.33% DM, ad lib. feeding) until the summer drought when low herbage mass would have restricted milk production. Serum Ca was adequate for lactating cows and changed little between months or between cows (mean 2.12 mmol Ca/l). No metabolic disorders relating to mineral deficiencies were observed. It appears that serum Pi in a high proportion of cows falls below the normal range during peak lactation without cows displaying clinical deficiency symptoms or a depression in butterfat production.

Phosphorus deficiency in a dairy herd

Phosphorus deficiency was diagnosed in a 90 cow seasonal supply dairy herd which showed low milk production, ill-thrift, infertility and osteophagia. Serum inorganic phosphorus and pasture phosphorus levels were low, pasture Ca:P ratios high and soil phosphorus levels very low; the soil phosphate retention value was 96%. The deficiency, which had probably existed for several years, was considered to be due to inadequate annual phosphate fertiliser applications on a high phosphate retaining soil. Phosphorus deficiency may have been exacerbated by the application of lime without phosphate several months before the onset of severe clinical disease. The finding of low sodium levels in pasture samples suggested that sodium deficiency may have co-existed and contributed to the clinical picture. Treatment, comprising bone flour dusting of pasture, water trough supplementation and phosphorus-containing injections, appeared to induce ovarian activity in anoestrous cows and suppress osteophagia, though controlled treatment trials were not performed. No improvement was noted in milk production or cow condition. Increased annual super-phosphate and reduced potassium applications were recommended, together with the monitoring of pasture and soil macro elements and serum phosphorus levels. A decision on whether to supplement with sodium would be based on the results of pasture monitoring, since a direct animal test is not currently available. It is suggested that phosphorus deficiency may not be uncommon in dairy herds in some North Island districts; based on the present case, the decline in New Zealand superphosphate quality in the 1970's and recently published data which has shown a high proportion of pasture phosphorus deficient sites in some North Island areas.

Effects of feeding varying levels of protein and phosphorus in relation to bone disorders in cattle

Steers were fed low or high protein diets with varying levels of phosphorus. Two steers on the low protein diet developed a disorder which clinically resembled osteomalacia after 21 weeks of experimental feeding, and other animals on the same diet showed varying degrees of lameness. The total fresh weight, total mineral content, and the calcium and phosphorus levels of the metacarpal bones were significantly lower in the low protein group. Total fresh weight, total ash content of the rib bones was also lower although there were no differences between groups in the calcium and phosphorus content of rib bones. There were significant differences between treatment groups in blood levels of calcium, phosphorus and protein. The carcase weight of high protein animals was significantly greater than that of the low protein animals. Phosphorus level in the diet had little effect on any tissue measurement. The results showed that a bone disorder could develop in animals fed adequate phosphorus but inadequate protein. The implications of the experiment are considered in relation to the levels of protein and phosphorus in pasture throughout northern Australia.

Phosphorus nutrition of beef cattle. 2. Relation of pasture phosphorus to phosphorus content of blood, hair and bone grazing steers

The phosphorus content was measured every three months in pasture and in blood, hair and bone of beef steers that had grazed pastures of low phosphorus content for 12 months. This was done to determine the effect that changes in pasture phosphorus levels had on the phosphorus content of animal tissue. The correlation coefficients between pasture phosphorus content and either the phosphorus content of hair or the concentration of inorganic phosphorus in plasma were not significant. The relationship between the phosphorus content of pasture (x) and dry fat-free rib-bone (y) was given by the equation y = 9.5 + 33.3x (r = 0.97; P &lt; 0.05). It was concluded that bone phosphorus content could provide the best estimate of the phosphorus status of grazing cattle because it significantly reflected variation in the phosphorus content of pasture whereas blood and hair failed to do so.

Seasonal variation of phosphorus in soil and pasture

Abstract Availability of soil phosphate to pasture plants, as indicated by rate of growth and phosphorus concentration in herbage dry matter, is typically greater in spring than in autumn and winter. The hypothesis that this apparent higher phosphate status of soils under pasture in spring is due to a build-up of available phosphate during the period of slow growth in winter has been examined by measurement of pasture and soil properties at monthly intervals over 14 months on seven widely differing soils in the Hawke's Bay and Wellington districts. The experimental areas were on developed pastures under rotational grazing. Rate of pasture growth, botanical composition of pasture, and concentration of phosphorus in the pasture species all followed the normal seasonal pattern. Anion-exchangeable phosphate, concentration of phosphate in O.O1M CaCl2, and phosphate retention showed significant changes over the summer, but there was little variation over the winterspring period to indicate a build-up of availab...

Wet season grazing of Townsville stylo pasture at Katherine, N.T

At Katherine, N.T., stocking rates of 1.33, 1.00, and 0.67 Shorthorn steers an acre for a period of 18 weeks in the wet season beginning January were imposed on established pastures sown to Townsville sty10 (Stylosanthes humilis) alone but subsequently invaded to varying degrees by annual grasses. The experiment was repeated over three years. There were no significant differences in mean liveweight gain per head over three years ; hence liveweight gain per acre at the heaviest stocking rate was approximately twice that at the lightest rate. The mean dry matter yield of grass increased significantly with decreasing stocking rate, but there were no significant differences between stocking rates in Townsville stylo dry matter yield, nitrogen yield, or phosphorus yield. Correlation coefficients were calculated using data from individual paddocks and years. There was a highly significant positive correlation between liveweight gain per head and pasture nitrogen yield, and between liveweight gain per head and pasture phosphorus yield.