yield response to N fertilizer is important in providing effective N management recommendations over a wide Efficient use of N fertilizer for corn (Zea mays L.) production range of soil-climate conditions, minimizing the potenis important for maximizing economic return and minimizing NO 3 leaching to groundwater. The objective of this study was to evaluate tial for negative environmental impacts. grain yield response to irrigation rate and N rate and timing forNumerous studies have emphasized the importance irrigated corn in the sandy soils along major Kansas waterways. Nitroof considering the effects of water management on NO 3 gen treatments included 300 and 250 kg N ha Ϫ1 applied at planting; movement under irrigated corn (Watts and Martin, 1981; 250 kg N ha Ϫ1 applied at planting (one-half) and sidedress (one-half); Hergert, 1986;Spalding et al., 2001). Endelman et al.185 kg N ha Ϫ1 applied at planting (one-third) and sidedress (two- (1974) reported that as little as 2.54 cm of irrigation or thirds); 125 kg N ha Ϫ1 applied at planting (one-fifth) and sidedress rainfall can move soil NO 3 15 to 20 cm in a loamy sand (two-fifths, two-fifths); and 0 kg N ha Ϫ1 . Nitrogen treatments were soil. Considering that the average rainfall duplicated at one site for each of two irrigation treatments (IS): 1.0ϫ from mid-April to mid-June in south-central Kansas is (optimal) and 1.25ϫ (25% Ͼ optimal). A split application of 185 kg 21.2 cm (Kansas State Univ. Res. and Ext., 2004), the N ha Ϫ1 was sufficient to achieve maximum corn yield at every location, and in most instances 125 kg N ha Ϫ1 was sufficient. These rates were

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Carbon sequestration in the terrestrial biosphere is critical to mitigating the increasing anthropogenic CO 2 content of the atmosphere. However, improved efficiency of methods for soil C measurement is important to better estimate terrestrial C inventories and fluxes at a regional and global scale. Laboratory based measurement of soil C involves intensive, time consuming, and costly methodology that limits applicability for large land areas. Recently, research efforts have focused on measuring soil C in situ using a variety of methods. These methods include Laser Induced Breakdown Spectroscopy (LIBS), Inelastic Neutron Scattering (INS), near-infrared spectroscopy (NIRS), and remote sensing. Basic fundamentals of each of these in situ methods for soil C determination are presented, and the differences among the methods and their relative advantages and disadvantages are discussed. AbbreviationsAVIRIS airborne visible/infrared imaging spectrometer INS inelastic neutron scattering LIBS laser-induced breakdown spectroscopy MDL minimum detection limit MIR mid-infrared NIR near-infrared NIRS near-infrared spectroscopy SEP standard error of prediction SOC soil organic carbon SOM soil organic matter

Fe deficiency is foliar application of Fe solutions. This method of correction usually alleviates chlorosis; how-Corn (Zea mays L.) grown on calcareous, high-pH soils is susceptiever, the results from a foliar application may be only ble to Fe deficiency, which can reduce grain yield by as much as 20%.temporary and actually depress the plant's Fe stress mech-The objective of this study was to evaluate several treatments of FeSO 4 anisms by preventing the increase in Fe-reducing capacthat could be used with precision-farming technologies to alleviate Fe deficiency in irrigated corn. Three sites in 1999 and four in 2000 were ity of the roots that would normally occur during Fe selected (based on a history of Fe deficiency) for small-plot (3 by deficiency (Rö mheld and Marschner, 1986b). Other in-12.2 m) studies in western Kansas. In 1999, five treatments, including tensively researched Fe sources include organic comfour rates of FeSO 4 ·H 2 O (0-81 kg ha Ϫ1 product) applied in the seed pounds, acidifying amendments, industrial by-products, row and one foliar treatment (chelated Fe), were evaluated. In 2000,and animal wastes (Olson, 1950;Wallace et al., 1976; two additional treatments, CaSO 4 ·2H 2 O (85 kg ha Ϫ1 product) and Thomas and Mathers, 1979). liquid FeSO 4 ·7H 2 O (91 kg ha Ϫ1 product) applied in the seed row, Researchers are faced with many challenges when were included. Grain yield increased linearly with increasing rates of working with Fe fertilizer. Cihacek (1984) observed that FeSO 4 ·H 2 O at four of seven site-years, increasing 0.02 Mg ha Ϫ1 for researchers find mixed results because treatments often each kilogram per hectare of FeSO 4 ·H 2 O applied. Based on yield show little or no visual effect on Fe chlorosis, grain responses observed in this study, 81 kg ha Ϫ1 FeSO 4 ·H 2 O was the most consistent treatment for correcting Fe deficiency in corn. If the average yields vary from year to year, or effective treatments are yield response obtained in this study can be achieved on 15% of an not economically feasible for the producer. Numerous individual cornfield, the expected return would be $3.00 ha Ϫ1 for the factors contribute to the inconsistent results, but perentire field. Current precision-farming technologies allow application haps the two biggest obstacles to overcome are temporal of FeSO 4 ·H 2 O only to areas susceptible to Fe deficiency. Employing and spatial variability. Temporal variability can be inthese technologies provides a practical solution to the spatial heterogeduced by variability in climatic conditions that affect soil neity of Fe deficiency in irrigated corn and increases the probability temperature and soil moisture and cause inconsistent of crop response to the fertilizer application.treatment responses. Spatial heterogeneity creates problems because Fe-deficient areas in a field are usually small and levels of plant-available soil Fe can vary within

cally in both the visible and near-infrared (NIR) wavelengths so that vegetative indices can be computed. Th e normalized ABSTRACT Nitrogen fertilizer management of sugarbeet (Beta vulgaris L.) continues to increase in importance with rising fertilizer costs and industry payments weighted toward crop quality. Our objective was to evaluate the use of an optical sensor for assessment of in-season sugarbeet N status, yield, and quality prediction and total N in foliage on the day of harvest. Six N fertilizer treatments, from 0 to 225 kg N ha -1 , were applied at three sites in Michigan in 2006 and four sites in 2007. Normalized diff erence vegetative indices (NDVIs) were measured at four growing degree day (GDD) intervals in 2006, fi ve intervals in 2007, and at harvest in both years with a red-band active sensor. Leaf biomass and root yield were determined at harvest, and root samples were collected for determination of sucrose content and clear juice purity. Th e NDVI readings were useful for diff erentiating control treatments from fertilized plots but were not able to identify a yield response threshold until late in the season. Midseason 1200 to 1400 GDD, 1900 to 2300 GDD, and harvest NDVI values were strongly related to recoverable white sucrose per area (R 2 = 0.89, 0.87, and 0.80, respectively). Harvest NDVI was strongly related to sugarbeet vegetation total N (R 2 = 0.87). Active sensing during the growing season shows promise as a means to estimate root yield and recoverable sugar in sugarbeet fi elds. Sensing on the day of harvest may improve rotational N management by providing an indication of N return to the cropping system.

Sorghum [Sorghum bicolor (L.) Moench] can be used as bioenergy crop for either biomass or sugar yield. Dry matter (DM) yield and nutrient removal information is needed if sorghum is to be planted in high-nutrient receiving areas such as swine (Sus scrofa domesticus) spray fi elds. Th e objectives of this 4-yr experiment (2012 through 2015) were to determine the eff ect of fi ve N fertilization rates (0, 67, 134, 201, and 268 kg N ha-1 yr-1) on DM yield and nutrient (N, P, and K) removal of cultivars Blade ES5200 (biomass) and M81-E (sweet). Th e DM yield of ES5200 plateaued at 18.5 and 18.9 Mg ha-1 in 2012 and 2014, respectively, when N rate was 67 kg ha-1. Th ere was no N fertilization eff ect on DM yield of M81-E, which were 11.1 and 15.0 Mg ha-1 in 2012 and 2014, respectively. Early season excess rainfall in 2013 and 2015 negatively aff ected yield of both sorghums. Nutrient removal for ES5200 was 87 to 139 kg N ha-1 , 20 to 23 for kg P ha-1 , and 187 to 205 kg K ha-1. For M81-E, nutrient removal was 52 to 118 kg N ha-1 , 8 to 20 for kg P ha-1 , and 92 to 156 kg K ha-1. Sorghum cultivars responded diff erently to N fertilization. High DM yield supports sorghum as a bioenergy crop, however, the relatively low nutrient removal rate may limit its utilization in nutrient-rich environments such as spray fi elds.

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Minimizing the risk of nitrate contamination along the waterways of the U.S. Great Plains is essential to continued irrigated corn production and quality water supplies. The objectives of this study were to quantify nitrate (NO(3)) leaching for irrigated sandy soils (Pratt loamy fine sand [sandy, mixed, mesic Lamellic Haplustalfs]) and to evaluate the effects of N fertilizer and irrigation management strategies on NO(3) leaching in irrigated corn. Two irrigation schedules (1.0x and 1.25x optimum) were combined with six N fertilizer treatments broadcast as NH(4)NO(3) (kg N ha(-1)): 300 and 250 applied pre-plant; 250 applied pre-plant and sidedress; 185 applied pre-plant and sidedress; 125 applied pre-plant and sidedress; and 0. Porous-cup tensiometers and solution samplers were installed in each of the four highest N treatments. Soil solution samples were collected during the 2001 and 2002 growing seasons. Maximum corn grain yield was achieved with 125 or 185 kg N ha(-1), regardless of the irrigation schedule (IS). The 1.25x IS exacerbated the amount of NO(3) leached below the 152-cm depth in the preplant N treatments, with a mean of 146 kg N ha(-1) for the 250 and 300 kg N preplant applications compared with 12 kg N ha(-1) for the same N treatments and 1.0x IS. With 185 kg N ha(-1), the 1.25x IS treatment resulted in 74 kg N ha(-1) leached compared with 10 kg N ha(-1) for the 1.0x IS. Appropriate irrigation scheduling and N fertilizer rates are essential to improving N management practices on these sandy soils.