Recovery of Fertilizer Nitrogen Under Field Conditions Using Nitrogen-15

An experiment was conducted under field conditions to study the movement and recovery of N15-enriched nitrogen fertilizer added to soil in the forms of NaNO2 and (NH4)2SO4. The plots consisted of the soil mass inside cylinders 30 or 60 cm in diameter, which were pressed into the soil to a depth of 45-60 cm. These plots were either seeded to sudangrass (sorghum sudanense) or left uncropped. The plant tops, roots, and the soil, by 15-cm layers, were analyzed for total N and excess N15 content. Recovery of added N15 from the 32 plots ranged between 96.3 and 101.8%, and averaged 99.0%. There was no significant difference in recovery of the fertilizer N due to the percent of excess N15 in the fertilizer, size of plot, exposure to natural rainfall, cropping, N source, or the time of application of the fertilizer. Wide variation in recovery of excess N15 occurred with core sampling and it was found necessary to remove, weigh, mix and subsample the entire soil mass from within the rims. The small amounts of unrecovered N were probably due to procedural errors in the field and laboratory, and leaching and root growth beyond the sampling zone. There was no indication of any N loss in the gaseous form. The fate of applied fertilizer N was followed under field conditions using N15-enriched nitrogen fertilizer applied to the soil in situ enclosed by large steel cylinders. Total recovery of the fertilizer N from these experiments after 8 weeks ranged from 88 to 96%, but dropped as low as 77% after 10 months. Recovery of the fertilizer N was greater from an ammonium source than from nitrate. Better recovery of fertilizer was obtained when the plots were cropped to sudangrass rather than left fallow. Doubling the rate of application of the fertilizer N from 336 to 672 kg/ha did not affect percent of total recovery. The 4 to 12% of fertilizer N unrecovered after 8 weeks appears to be due to a loss in the gaseous form, since special precautions were taken to restrict leaching and to eliminate errors in sampling and analysis

Novel genetic loci associated with hippocampal volume

The hippocampal formation is a brain structure integrally involved in episodic memory, spatial navigation, cognition and stress responsiveness. Structural abnormalities in hippocampal volume and shape are found in several common neuropsychiatric disorders. To identify the genetic underpinnings of hippocampal structure here we perform a genome-wide association study (GWAS) of 33,536 individuals and discover six independent loci significantly associated with hippocampal volume, four of them novel. Of the novel loci, three lie within genes (ASTN2, DPP4 and MAST4) and one is found 200 kb upstream of SHH. A hippocampal subfield analysis shows that a locus within the MSRB3 gene shows evidence of a localized effect along the dentate gyrus, subiculum, CA1 and fissure. Further, we show that genetic variants associated with decreased hippocampal volume are also associated with increased risk for Alzheimer's disease (rg =-0.155). Our findings suggest novel biological pathways through which human genetic variation influences hippocampal volume and risk for neuropsychiatric illness