ricultural fields, and increased use of manufactured N fertilizers. Balancing the amount of N needed for optimum plant growth whileLess than 50 yr ago, corn (Zea mays L.) was generally minimizing the NO 3 that is transported to ground and surface waters grown in rotation with cereal crops and forage legumes remains a major challenge for everyone attempting to understand such as alfalfa (Medicago sativa L.), red clover (Trifoand improve agricultural nutrient use efficiency. Our objectives for lium pratense L.), and sweetclover (Melilotus spp.). this review are to examine how changes in agricultural management practices during the past century have affected N in midwestern soils Through biological N fixation, the legumes generally and to identify the types of research and management practices needed increased the amount of residual N in the soil profile. to reduce the potential for nonpoint NO 3 leakage into water resources. Cycling of this residual, biologically fixed N along with Inherent soil characteristics and management practices contributing N mineralized from SOM added with animal manure to nonpoint NO 3 loss from midwestern soils, the impact of NO 3 loading or deposited through rainfall was the primary process on surface water quality, improved N management strategies, and through which corn and other grain crops obtained N. research needs are discussed. Artificial drainage systems can have a Following World War II, increased availability of significant impact on water quality because they behave like shallow, commercial N fertilizer and decreased demand for fordirect conduits to surface waters. Nonpoint loss of NO 3 from fields age crops led to a significant reduction in crop rotations to water resources, however, is not caused by any single factor. Rather, and a general substitution of purchased N for biological it is caused by a combination of factors, including tillage, drainage, N. In Iowa, forage pasture represented more than 33.6% crop selection, soil organic matter levels, hydrology, and temperature and precipitation patterns. Strategies for reducing NO 3 loss through (3 389 160 ha) of the state's total cropped area at the drainage include improved timing of N application at appropriate end of World War II (U.S. Dep. of Commerce, Bureau rates, using soil tests and plant monitoring, diversifying crop rotations, of the Census, 1945). By 1997, forage pasture area in using cover crops, reducing tillage, optimizing N application tech-

De novo protein design holds promise for creating small stable proteins with shapes customized to bind therapeutic targets. We describe a massively parallel approach for designing, manufacturing and screening mini-protein binders, integrating large-scale computational design, oligonucleotide synthesis, yeast display screening and next-generation sequencing. We designed and tested 22,660 mini-proteins of 37–43 residues that target influenza haemagglutinin and botulinum neurotoxin B, along with 6,286 control sequences to probe contributions to folding and binding, and identified 2,618 high-affinity binders. Comparison of the binding and non-binding design sets, which are two orders of magnitude larger than any previously investigated, enabled the evaluation and improvement of the computational model. Biophysical characterization of a subset of the binder designs showed that they are extremely stable and, unlike antibodies, do not lose activity after exposure to high temperatures. The designs elicit little or no immune response and provide potent prophylactic and therapeutic protection against influenza, even after extensive repeated dosing.

Balancing the amount of N needed for optimum plant growth while minimizing the NO3 that is transported to ground and surface waters remains a major challenge for everyone attempting to understand and improve agricultural nutrient use efficiency. Our objectives for this review are to examine how changes in agricultural management practices during the past century have affected N in midwestern soils and to identify the types of research and management practices needed to reduce the potential for nonpoint NO3 leakage into water resources. Inherent soil characteristics and management practices contributing to nonpoint NO3 loss from midwestern soils, the impact of NO3 loading on surface water quality, improved N management strategies, and research needs are discussed. Artificial drainage systems can have a significant impact on water quality because they behave like shallow, direct conduits to surface waters. Nonpoint loss of NO3 from fields to water resources, however, is not caused by any single factor. Rather, it is caused by a combination of factors, including tillage, drainage, crop selection, soil organic matter levels, hydrology, and temperature and precipitation patterns. Strategies for reducing NO3 loss through drainage include improved timing of N application at appropriate rates, using soil tests and plant monitoring, diversifying crop rotations, using cover crops, reducing tillage, optimizing N application techniques, and using nitrification inhibitors. Nitrate can also be removed from water by establishing wetlands or biofilters. Research that is focused on understanding methods to minimize NO3 contamination of water resources should also be used to educate the public about the complexity of the problem and the need for multiple management strategies to solve the problem across agricultural landscapes.

in artificially drained soils, have been conducted over a much briefer time (Angle et al., 1993; Rasse et al., The relationships between N fertilizer rate, yield, and NO 3 leaching 1999). In one of the first controlled studies, Baker et need to be quantified to develop soil and crop management practices al. (1975) found that the concentration of NO 3 in tile that are economically and environmentally sustainable. From 1996 through 1999, we measured yield and NO 3 loss from a subsurface drainage water averaged 21 mg N L Ϫ1 and the losses drained field in central Iowa at three N fertilizer rates: a low (L) rate averaged approximately 30 kg N ha Ϫ1 yr Ϫ1 for a N fertilof 67 kg ha Ϫ1 in 1996 and 57 kg ha Ϫ1 in 1998, a medium (M) rate of izer application of 112 kg N ha Ϫ1 on corn grown in 135 kg ha Ϫ1 in 1996 and 114 kg ha Ϫ1 in 1998, and a high (H) rate of rotation with unfertilized oat (Avena sativa L.) or soy-202 kg ha Ϫ1 in 1996 and 172 kg ha Ϫ1 in 1998. Corn (Zea mays L.) bean. In continuous corn production, Randall and Iragaand soybean [Glycine max (L.) Merr.] were grown in rotation with varapu (1995) found flow-weighted NO 3 concentrations N fertilizer applied in the spring to corn only. For the L treatment, during an 11-yr period of applying 200 kg N ha Ϫ1 to NO 3 concentrations in the drainage water exceeded the 10 mg N L Ϫ1 average 13.4 and 12.0 mg N L Ϫ1 for conventional-tillage maximum contaminant level (MCL) established by the USEPA for and no-tillage systems, respectively. In comparing the drinking water only during the years that corn was grown. For the effect of N fertilizer rate, Baker and Johnson (1981) M and H treatments, NO 3 concentrations exceeded the MCL in all found that increasing the fertilizer rate from 100 to 250 years, regardless of crop grown. For all years, the NO 3 mass loss in tile drainage water from the H treatment (48 kg N ha Ϫ1) was significantly kg N ha Ϫ1 on corn, grown in rotation with either soybean greater than the mass losses from the M (35 kg N ha Ϫ1) and L (29 or oat, doubled the NO 3 concentration in tile drainage kg N ha Ϫ1) treatments, which were not significantly different. The from 20 to 40 mg N L Ϫ1. Similar results have been reeconomically optimum N fertilizer rate for corn was between 67 and ported by Gast et al. (1978) for N fertilizer applied to 135 kg ha Ϫ1 in 1996 and 114 and 172 kg ha Ϫ1 in 1998, but the net N

Soil conservation tillage systems, including ridge-tillage, often reduce surface water contamination by pesticides because soil erosion and surface runoff are reduced. However, the effects on losses through subsurface drainage tile are somewhat uncertain. Our field study quantified the effects of four tillage practices in continuous corn (Zea mays L.) and corn-soybean [Glycine max (L.) Merr] rotations on herbicide and nitrate N losses in tile drainage water. Fertilizer and pesticide application methods were uniform for ridge, moldboard, chisel, and no-till systems. Pesticide and nitrate N leaching losses were significantly affected by crop rotation. Tillage practice had little influence on nitrate N and pesticide losses to the subsurface drainage water within a corn-soybean rotation. However, ridge-till and no-till resulted in larger losses of atrazine than the moldboard plow and chisel based systems under continuous corn. Tillage system did not affect the timings of peak tile flow occurrences, although peak tile flow volume was affected by tillage, presumably because each system bad its own macropore system related to preservation or annual destruction of biopores by tillage. Corn yields were significantly higher under corn-soybean rotation than with continuous-corn for all tillage practices. These results indicate that continuous corn production is not an environmentally sustainable practice for this area because it resulted in higher nitrate N leaching losses to groundwater, received higher Napplications, and resulted in lower corn yields than the corn-soybean rotation. The results also reinforce the need for studies on chemical placement, rate, and timing for various tillage practices to reduce tile drainage losses of agricultural chemicals.