RESUMEN
The use of grasses as cover crops in the off-season of cash crops under no-till has been largely adopted. However, soil phosphorus (P) uptake was previously shown to be reduced when ruzigrass is introduced in the rotation, affecting the viability and sustainability of this cropping system. The objective of this study was to assess the effect of ruzigrass on soil P availability and desorption kinetics under different P fertilizer application rates. A long-term field experiment where soybean (Glycine max) has been grown in rotation with ruzigrass (Urochloa ruziziensis) or fallow for 10â¯years, with the application of 0, 13, and 26â¯kgâ¯ha-1 of P, was evaluated for two consecutive years. Soil P desorption kinetics was assessed using diffusive equilibrium (DET) and gradient in thin films (DGT) techniques, as well as the DGT-induced fluxes in soils model (DIFS). Microbial biomass P (MBP) was assessed to verify if soil solution P (PDET) was reduced due to immobilization by microorganisms. Ruzigrass reduced MBP and PDET especially when P fertilizer was applied. The concentration of labile P (PDGT) was also lower after ruzigrass than in fallow. The soil ability to resupply P to soil solution was lower after ruzigrass regardless of P rates due to a slower desorption in response to the perturbation imposed by DGT. Growing ruzigrass as cover crop in the soybean off-season decreases soil P availability regardless of P fertilizer application rates by fundamentally reducing P mobility and P resupply from soil solid phase into soil solution.
RESUMEN
BACKGROUND: The effect of phytase supplementation with respect to a high sorghum grain diet on sheep voluntary feed intake, apparent nutrient digestibility, ruminal fermentation, phosphorus (P) excretion and blood serum P concentration was evaluated. RESULTS: Phytase supplementation significantly decreased fecal P excretion (P = 0.003), resulting in a 26% decrease in relation to the phytase free diet. Dry matter intake, nutrient digestibility, ruminal butyrate and serum P were not (P > 0.10) affected by the phytase level. Neutral detergent digestibility showed a tendency to increase linearly (P = 0.10) with increasing phytase levels. Ruminal pH was lower for phytase supplemented sheep, with a significant decrease (P = 0.007) at 9 h post feeding, whereas ruminal ammonia-N at 3 h post feeding was lower (P = 0.004) for the phytase treatment groups, resulting in a decreasing linear response (P = 0.001) with an increasing phytase dose. Duodenal pH was significantly reduced at 6 h post feeding. Propionate tended (P = 0.051) to be increased linearly as the phytase supplementation level increased. CONCLUSION: Exogenous phytase supplementation of high sorghum grain diets significantly decreased fecal P excretion in Rambouillet rams. Phytase supplementation appears to affect neutral detergent fiber digestibility, duodenal and ruminal pH, ammonia and propionate. © 2018 Society of Chemical Industry.
Asunto(s)
6-Fitasa/administración & dosificación , Alimentación Animal/análisis , Fósforo/sangre , Rumen/metabolismo , Ovinos/metabolismo , 6-Fitasa/metabolismo , Amoníaco/metabolismo , Animales , Disponibilidad Biológica , Fibras de la Dieta/metabolismo , Suplementos Dietéticos/análisis , Heces/química , Fermentación , Sorghum/metabolismoRESUMEN
Phytases are enzymes involved in organic phosphorus cycling in nature and widely used as feed additives in animal diets. Thermal tolerance is a desired property of phytases. The objectives of this study were to screen and characterize bacterial phytases from Chilean hydrothermal environments. In this study, 60% (30 of 63) of screened thermophilic (60 °C) isolates showed phytase activity in crude protein extracts. The characterization of phytase from two selected isolates (9B and 15C) revealed that both isolates produce phytases with a pH optimum at 5.0. The temperature optimum for phytate dephosphorylation was determined to be 60 and 50 °C for the phytases from the isolates 9B and 15C, respectively. Interestingly, the phytase from the isolate 15C showed a residual activity of 46% after incubation at 90 °C for 20 min. The stepwise dephosphorylation of phytate by protein extracts of the isolates 9B and 15C was verified by HLPC analysis. Finally, the isolates 9B and 15C were identified by partial sequencing of the 16S rRNA gene as members of the genera Bacillus and Geobacillus, respectively.
Asunto(s)
6-Fitasa/química , 6-Fitasa/metabolismo , Bacterias/enzimología , Proteínas Bacterianas/química , Proteínas Bacterianas/metabolismo , Respiraderos Hidrotermales/microbiología , 6-Fitasa/genética , Bacterias/clasificación , Bacterias/genética , Bacterias/aislamiento & purificación , Proteínas Bacterianas/genética , Estabilidad de Enzimas , Concentración de Iones de Hidrógeno , Cinética , TemperaturaRESUMEN
Phytate is one of the most abundant sources of organic phosphorus (P) in soils, but must be mineralized by phytase-producing bacteria to release P for plant uptake. Microbial inoculants based on Bacillus spp. have been developed commercially, but few studies have evaluated the ecology of these bacteria in the rhizosphere or the types of enzymes that they produce. Here, we studied the diversity of aerobic endospore-forming bacteria (EFB) with the ability to mineralize phytate in the rhizosphere of pasture plants grown in volcanic soils of southern Chile. PCR methods were used to detect candidate phytase-encoding genes and to identify EFB bacteria that carry these genes. This study revealed that the phytate-degrading EFB populations of pasture plants included species of Paenibacillus and Bacillus, which carried genes encoding ß-propeller phytase (BPP). Assays of enzymatic activity confirmed the ability of these rhizosphere isolates to degrade phytate. The phytase-encoding genes described here may prove valuable as molecular markers to evaluate the role of EFB in organic P mobilization in the rhizosphere.