Watershed and global-scale nitrogen (N) budgets indicate that the majority of the N surplus in anthropogenic landscapes does not reach the coastal oceans. While there is general consensus that this 'missing' N either exits the landscape via denitrification or is retained within watersheds as nitrate or organic N, the relative magnitudes of these pools and fluxes are subject to considerable uncertainty. Our study, for the first time, provides direct, large-scale evidence of N accumulation in the root zones of agricultural soils that may account for much of the 'missing N' identified in mass balance studies. We analyzed long-term soil data (1957-2010) from 2069 sites throughout the Mississippi River Basin (MRB) to reveal N accumulation in cropland of 25-70 kg ha −1 yr −1 , a total of 3.8±1.8 Mt yr −1 at the watershed scale. We then developed a simple modeling framework to capture N depletion and accumulation dynamics under intensive agriculture. Using the model, we show that the observed accumulation of soil organic N (SON) in the MRB over a 30 year period (142 Tg N) would lead to a biogeochemical lag time of 35 years for 99% of legacy SON, even with complete cessation of fertilizer application. By demonstrating that agricultural soils can act as a net N sink, the present work makes a critical contribution towards the closing of watershed N budgets.

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Samples of 255 noncalcareous A, Ap, and AB horizons from selected major land resource areas (MLRA) in the north central USA were used to develop equations for predicting organic C content, as determined with a Leco C analyzer, from weight loss‐on‐ignition (LOI). Organic C concentrations of the samples ranged from 1.09 to 114.6 g kg−1 Within each MLRA, strong linear relationships were observed between LOI and organic C measured by the Leco instrument, with r2 ranging from 0.94 to 0.98. Predictive equations developed by least‐squares regression were significantly different for individual MLRA's. Loss‐on‐ignition is a rapid, inexpensive, and accurate method for estimating organic C concentration in soils of the north central USA. We recommend that unique predictive equations be developed for individual soil‐geographic regions.

Liu, X., Burras, C. L., Kravchenko, Y. S., Duran, A., Huffman, T., Morras, H., Studdert, G., Zhang, X., Cruse, R. M. and Yuan, X. 2012. Overview of Mollisols in the world: Distribution, land use and management. Can. J. Soil Sci. 92: 383–402. Mollisols – a.k.a., Black Soils or Prairie Soils – make up about 916 million ha, which is 7% of the world's ice-free land surface. Their distribution strongly correlates with native prairie ecosystems, but is not limited to them. They are most prevalent in the mid-latitudes of North America, Eurasia, and South America. In North America, they cover 200 million ha of the United States, more than 40 million ha of Canada and 50 million ha of Mexico. Across Eurasia they cover around 450 million ha, extending from the western 148 million ha in southern Russia and 34 million ha in Ukraine to the eastern 35 million ha in northeast China. They are common to South America's Argentina and Uruguay, covering about 89 million and 13 million ha, respectively. Mollisols are often recognized as inherently productive and fertile soils. They are extensively and intensively farmed, and increasingly dedicated to cereals production, which needs significant inputs of fertilizers and tillage. Mollisols are also important soils in pasture, range and forage systems. Thus, it is not surprising that these soils are prone to soil erosion, dehumification (loss of stable aggregates and organic matter) and are suffering from anthropogenic soil acidity. Therefore, soil scientists from all of the world's Mollisols regions are concerned about the sustainability of some of current trends in land use and agricultural practices. These same scientists recommend increasing the acreage under minimum or restricted tillage, returning plant residues and adding organic amendments such as animal manure to maintain or increase soil organic matter content, and more systematic use of chemical amendments such as agricultural limestone to replenish soil calcium reserves.

Based on this idea, greater legume richness and diversity may aid legume contributions to pasture swards used Pastures typically have diverse landscapes, and resulting soil condifor animal production. tions and plant composition can vary within small area units. This study was performed to quantify the spatial variation in legume contri-Information is also lacking that quantifies changes in bution to the plant community when seeded into established perennial legume composition across pasture landscapes, especool-season grass pastures. Pastures were interseeded with an 11cially under grazed conditions. Information regarding legume mixture and divided into three stocking methods (continuous, landscape positions and plant growth mostly involves rotational, and nongrazed), with each stocking method containing five landscape effects on row crop and cereal grain produclandscape positions (summit, backslope, toeslope, opposite backslope,

The quantification of soil organic C (SOC) concentrations is becoming increasingly more desirable because of environmental and economic concerns regarding the reactivity of SOC with pesticides, fertilizers, and waste materials. The objectives of this study were to quantify soil color organic C relationships and to quantify soil particle‐size organic C relationships for Ap horizons in north central Iowa. All of the 130 soils examined developed in glacigenic diamicton or local hillslope sediment derived from glacigenic diamicton. A Minolta CR‐310 chroma meter was used to quantify the percentage of reflectance, and Munsell value and chroma for both air‐dry and moist soils. Organic C concentration of the sample set ranged from 4.4 to 70.8 g kg−1 Significant relationships were observed between organic C concentration and percentage of reflectance (r2 = 0.77 moist, r2 = 0.74 air‐dry), Munsell value (r2 = 0.77 moist, r2 = 0.74 air‐dry), Munsell chroma (r2 = 0.68 moist, r2 = 0.77 air‐dry), the percentage of sand (r2 = 0.74), the percentage of clay (r2 = 0.71), and geometric mean particle diameter (GMPD) (r2 = 0.74). Logarithmic relationships existed for reflectance, Munsell value and chroma, and GMPD while linear relationships were observed for sand and clay contents. Chroma meter soil color measurements and particle‐size data are useful predictors of organic C concentrations for Ap horizons in north central Iowa. Evidence from this study and the literature suggest that unique relationships exist for different soil landscapes.

Tall fescue (Festuca arundinacea Schreb.