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Background: Although phytase has been widely used in poultry nutrition, the effects of the enzyme on broilers fed low levels of phosphorus are poorly understood. Objective: To evaluate the effects of two commercial phytases on live performance and bone quality of broilers fed diets with normal and reduced levels of phosphorus. Methods: Two experiments were conducted with four treatments and six repetitions with 30 birds each, for a total of 24 groups. The first experiment (Exp. I) used a reference level of available phosphorus (AP) with four treatments, as follows: Positive control= 0.45% AP starter diet/0.40% AP grower diet without phytase; Phytase X= 0.35% AP starter diet/0.30% AP grower diet + Phytase X; Phytase Y= 0.35% AP starter diet/0.30% AP grower diet + Phytase Y; and Negative control= 0.35% AP starter diet/0.30% AP grower diet, without phytase. In experiment II (Exp. II) the same treatments were used, but AP levels were reduced by 0.10%. The variables analyzed were: performance from one to 35 days, and bone quality at 35 days of age. Both experiments were analyzed using a completely randomized design. Results: In Exp. I, the positive control resulted in greater body weight gain (2,558 g; p<0,05) compared to Phytase Y (2,470 g) and negative control (2,472 g), and better feed conversion ratio (1.48; p<0,05) than the negative control (1.51). However, when phosphorus was reduced in Exp. II, the positive control and treatments with Phytase X showed better results (p<0.01) for feed intake (3,608 g and 3,593 g, respectively) and weight gain (2,430 g and 2,400 g, respectively) compared to the negative control (2,889 g of feed intake and 1,915 g of weight gain; p<0.01), which also presented low bone ash (36.8%) and phosphorus in the tibia (5.48%; p<0.01). Conclusion: Reducing AP concentration in diets not added with phytase negatively affects weight gain and feed intake of broilers.

In this study, the effects were investigated of salinity, foliar and soil applications of humic substances on the growth and mineral nutrients uptake of Corn (Hagein, Fardy10), and the comparison was carried out of the soil and foliar applications of humic acid treatments at different NaCl levels. Soil organic contents are one of the most important parts that they directly affect the soil fertility and textures with their complex and heterogenous structures although they occupy a minor percentage of the soil weight. Humic acids are an important soil component that can improve nutrient availability and impact on other important chemical, biological, and physical properties of soils. The effects of foliar and soil applications of humic substances on the plant growth and some nutrient elements uptake of Corn (Hagein, Fardy10) grown at various salt concentrations were examined. Sodium chloride was added to the soil to obtain 20 and 60mM saline conditions. Solid humus was applied to the soil one month before planting and liquid humic acids were sprayed on the leaves twice on 20th and 40th day after seedling emergence. The application doses of solid humus were 0, 2 and 4 g/kg and those of liquid humic acids were 0, 0.1 and 0.2%. Salinity negatively affected the growth of corn; it also decreased the dry weight and the uptake of nutrient elements except for Na and Mn. Soil application of humus increased the N uptake of corn while foliar application of humic acids increased the uptake of P, K, Mg,Na,Cu and Zn. Although the effect of interaction between salt and soil humus application was found statistically significant, the interaction effect between salt and foliar humic acids treatment was not found significant. Under salt stress, the first doses of both soil and foliar application of humic substances increased the uptake of nutrients.

Global biogeochemical models have improved dramatically in the last decade in their representation of the biosphere. Although leaf area data are an important input to such models and are readily available globally, global root distributions for modeling water and nutrient uptake and carbon cycling have not been available. This analysis provides global distributions for fine root biomass, length, and surface area with depth in the soil, and global estimates of nutrient pools in fine roots. Calculated root surface area is almost always greater than leaf area, more than an order of magnitude so in grasslands. The average C:N:P ratio in living fine roots is 450:11:1, and global fine root carbon is more than 5% of all carbon contained in the atmosphere. Assuming conservatively that fine roots turn over once per year, they represent 33% of global annual net primary productivity.

Phosphorus (P) is an essential element for all life forms. It is a mineral nutrient. Orthophosphate is the only form of P that autotrophs can assimilate. Extracellular enzymes hydrolyze organic forms of P to phosphate. Eutrophication is the overenrichment of receiving waters with mineral nutrients. The results are excessive production of autotrophs, especially algae and cyanobacteria. This high productivity leads to high bacterial populations and high respiration rates, leading to hypoxia or anoxia in poorly mixed bottom waters and at night in surface waters during calm, warm conditions. Low dissolved oxygen causes the loss of aquatic animals and release of many materials normally bound to bottom sediments including various forms of P. This release of P reinforces the eutrophication. Excessive concentrations of P is the most common cause of eutrophication in freshwater lakes, reservoirs, streams, and headwaters of estuarine systems. In the ocean, N becomes the key mineral nutrient controlling primary production. Estuaries and continental shelf waters are a transition zone, where excessive P and N create problems. It is best to measure and regulate total P inputs to whole aquatic ecosystems, but for an easy assay it is best to measure total P concentrations, including particulate P, in surface waters or N/P atomic ratios in phytoplankton

Phosphorus deficiency-induced metabolic changes related to exudation of carboxylic acids and protons were compared in roots of wheat (Triticum aestivum L. cv Haro), tomato (Lycopersicon esculentum L., cv. Moneymaker), chickpea (Cicer arietinum) and white lupin (Lupinus albus L. cv. Amiga), grown in a hydroponic culture system. P deficiency strongly increased the net release of protons from roots of tomato, chickpea and white lupin, but only small effects were observed in wheat. Release of protons coincided with increased exudation of carboxylic acids in roots of chickpea and white lupin, but not in those of tomato and wheat. P deficiency-induced exudation of carboxylic acids in chickpea and white lupin was associated with a larger increase of carboxylic acid concentrations in the roots and lower accumulation of carboxylates in the shoot tissue compared to that in wheat and tomato. -Citric acid was one of the major organic acids accumulated in the roots of all investigated species in response to P deficiency, and this was associated with increased activity and enzyme protein levels of PEP carboxylase, which is required for biosynthesis of citrate. Accumulation of citric acid was most pronounced in the roots of P-deficient white lupin, chickpea and tomato. Increased PEP carboxylase activity in the roots of these plants coincided with decreased activity of aconitase, which is involved in the breakdown of citric acid in the TCA cycle. In the roots of P-deficient wheat plants, however, the activities of both PEP carboxylase and aconitase were enhanced, which was associated with little accumulation of citric acid. The results suggest that P deficiency-induced exudation of carboxylic acids depends on the ability to accumulate carboxylic acids in the root tissue, which in turn is determined by biosynthesis, degradation and partitioning of carboxylic acids or related precursors between roots and shoot. In some plant species such as white lupin, there are indications for a specific transport mechanism (anion channel), involved in root exudation of extraordinary high amounts of citric acid.

Background: Exogenous enzyme supplementation is an effective and costsaving mechanism for increasing the availability of dietary nutrients by increasing digestion and reducing excretion. Objective: To evaluate the effects of phytase supplementation on performance, egg quality, and economic parameters in commercial laying hens fed reducednutrient diets from 70 weeks of age. Methods: Novogen White® commercial laying hens (n=256) were randomly allocated to four treatment groups, with eight replicates of eight hens in each group: PC (positive control): conventional diet not supplemented with phytase; diet with reduced levels (RN) of P (0.12%), Ca (0.10%), and ME (14 kcal/kg), and supplemented with 300 phytase units (FTU/kg; RN300FTU); diet with reduced levels of P (0.16%), Ca (0.13%), ME (18 kcal/kg), CP (8%), synthetic amino acids (0.01%), and supplemented with 600 FTU phytase/kg (RN600FTU); and diet with reduced levels of P (0.18% P), Ca (0.15%), ME (20 kcal/kg), CP (20%), synthetic amino acids (0.01%), and supplemented with 900 FTU phytase/kg (RN900FTU). Results: The layers fed the RN300FTU diet had 2.68% higher egg production than those fed the PC diet. Egg mass produced by PC and RN300FTUfed hens was statistically similar. Eggshell thickness was increased in PCfed hens. Feed cost for the RN900FTU diet was approximately 9% lower compared with that of the PC diet. Conclusion: The best performance and economic results were achieved when layers were fed a reducednutrient diet supplemented with 300 FTU phytase.

The importance of P originating from agricultural sources to the nonpoint source pollution of surface waters has been an environmental issue for decades because of the well-known role of P in eutrophication. Most previous research and nonpoint source control efforts have emphasized P losses by surface erosion and runoff because of the relative immobility of P in soils. Consequently, P leaching and losses of P via subsurface runoff have rarely been considered important pathways for the movement of agricultural P to surface waters. However, there are situations where environmentally significant export of P in agricultural drainage has occurred (e.g., deep sandy soils, high organic matter soils, or soils with high soil P concentrations from long-term overfertilization and/or excessive use of organic wastes). In this paper we review research on P leaching and export in subsurface runoff and present overviews of ongoing research in the Atlantic Coastal Plain of the USA (Delaware), the midwestern USA (Indiana), and eastern Canada (Quebec). Our objectives are to illustrate the importance of agricultural drainage to nonpoint source pollution of surface waters and to emphasize the need for soil and water conservation practices that can minimize P losses in subsurface runoff

Phosphorus in runoff from agricultural land is an important component of nonpoint-source pollution and can accelerate eutrophication of lakes and streams. Long-term land application of P as fertilizer and animal wastes has resulted in elevated levels of soil P in many locations in the USA. Problems with soils high in P are often aggravated by the proximity of many of these areas to P-sensitive water bodies, such as the Great Lakes, Chesapeake and Delaware Bays, Lake Okeechobee, and the Everglades. This paper provides a brief overview of the issues and options related to management of agricultural P that were discussed at a special symposium titled, \"Agricultural Phosphorus and Eutrophication,\" held at the November 1996 American Society of Agronomy annual meetings. Topics discussed at the symposium and reviewed here included the role of P in eutrophication; identification of P-sensitive water bodies; P transport mechanisms; chemical forms and fate of P; identification of P source areas; modeling of P transport; water quality criteria; and management of soil and manure P, off-farm P inputs, and P transport processes

An experiment was conducted to investigate the effect of various organic acid (OA) supplementation on phosphorus (P) and nitrogen (N) retention by rainbow trout fed low fishmealbased diets. Six experimental diets were formulated, and diet 0.5P was arranged as a positive control diet with 0.5% calcium phosphate and OP as a negative control without additional P. Diets CA and LA were supplemented with 1% citric (CA), and lactic (LA) acids, respectively, and diets MHA and LTE were supplemented with 1% methionine hydroxy analog (MHA) and 1% liquid trace elements (LTE), respectively. Fish fed CA and LTE showed similar growth to that of the positive control diet. P retention was lowest in the 0.5P group and was elevated with CA and LTE diets. Therefore, in this study it is suggested that it might not be necessary to supplement the low fishmeal-based diet of rainbow trout with P if certain organic acids such as CA are added.