Sixteen winter annual cover crop cultivars were grown in North Carolina to determine total N accumulation, biological N fi xation (BNF) potential, and compatibility with a roller-crimper-terminated organic corn (Zea mays L.) production system. Cover crops and termination dates were tested in a stripped block design. Treatments included hairy vetch (Vicia villosa Roth), common vetch (Vicia sativa L.), crimson clover (Trifolium incarnatum L.), Austrian winter pea (Pisum sativum L.), berseem clover (Trifolium alexandrinum L.), subterranean clover (Trifolium subterraneum L.), narrow leaf lupin (Lupinus angustifolius L.), and Balansa clover (Trifolium michelianum Savi.), as well as bicultures of rye (Secale cereale L.), hairy vetch, and Austrian winter pea. Roller-crimper termination occurred in mid-April, early May, and mid-May. Total biomass, N concentration, and C/N ratios were determined for cover crops at all roll times and natural 15 N abundance at the optimal kill date. Hairy vetch and crimson clover monocultures had the greatest overall biomass in 2009, and bicultures the greatest biomass in 2010. Crimson clover successfully terminated in late April, hairy vetch and Austrian winter pea in mid-May, and berseem clover and common vetch in late May. All cover crops except lupin and subterranean clover derived between 70 and 100% of their N from the atmosphere. Corn response to cover crop mulches was signifi cantly aff ected by the time of rolling, with poor stands resulting from competition with insuffi ciently terminated mulches. Crimson, Balansa, and subterranean clover mulches resulted in poor corn yields despite relatively high levels of total N. Th e highest corn yields were achieved in hairy vetch and rye plus hairy vetch bicultures.

PurposeThis paper explores the historical development of POE in order to provide a contextual backdrop to current discussions.Design/methodology/approachThis paper attempts to establish what POE is and does, and explores POE methodologies.FindingsThis paper concludes that the fact that this topic is extensively discussed highlights a growing frustration with the lack of progress toward POE becoming a mainstream activity in the process of building procurement. Other findings include POE's exclusion from professional curricula; who pays for POE? And issues with professional liability and its contribution to this lack of use.Practical implicationsThe paper presents the benefits accrued by stakeholders in the building procurement process, and the barriers to the adoption of POE that need to be addressed.Originality/valueThis literature review suggests that despite the trials and tribulations, POE has progressed from a one dimensional feedback process to a multidimensional process that, as an integrated element, can help drive the building procurement process forward. The paper presents an objective overview of literary discourse around POE, its potential and limitations.

This study examines the role of canopy trees in the formation and maintenance of different herb microhabitats in a mixed mesophytic forest stand. Herb abundance and reproductive success were recorded in 54 circular plots under seven species of canopy trees and in 15 circular control plots>2 m from any tree. Soil moisture, soil nutrient levels, litter depth, and light intensity were measured in a subset of these plots. Ordination of plots by both herb relative abundance and by reproductive success of common species indicated that herb assemblages under most canopy tree species were similar to those away from trees. However, herb assemblages under Fagus grandifolia trees differed moderately from the others while plots under Quercus alba trees supported significantly different herb assemblages. Analyses of variance revealed that several herb species occurred at significantly closer mean distance to the base of Q. alba or Fagus trees or at higher densities under these tree species. Soils around Q. alba trees had significantly higher concentrations of calcium and sulfate ions, and higher pH than plots under other tree species and control plots. This correlated closely with Q. alba stemflow which had higher concentrations of calcium and sulfate ions and lower concentrations of hydrogen ions than stemflow from other trees at this site. The slightly lower soil pH near the base of Fagus trees may have been related to the high volumes of stemflow produced by this species. Stepwise regression showed significant correlations between abundances of five common herb species and soil nutrient patterns. Maintenance of spatial heterogeneity in forest floor resources by the presence of different species of canopy trees may therefore be important in the maintenance of diversity in these understory herb communities.

resulted in the highest yields in these fields. Nitrogen applications at GS-25 can stimulate tiller development As no-till acreage increases, N management guidelines need rein southeastern wheat production because winter wheat examination due to the potential effects of surface residue on N transformations and crop development. Our objectives were to deter-does not enter a dormant state in these southern latmine: (i) if N applied at Zadok's Growth Stage (GS) 25 improves itudes. grain yield of no-till winter wheat (Triticum aestivum L.), (ii) if any Applying N at GS-25 to increase tiller density and yield increase was the result of increased spring tillering, and (iii) if yield (Scharf and Alley, 1993) may be even more importhere is a critical tiller density above which N application at GS-25 tant in no-till wheat because tiller development is often in no-till wheat was not required. Research was conducted at three slower compared with conventional tillage (Weisz and sites in North Carolina with seven site-years between fall 1996 and Bowman, 1999). Tiller densities are often very low in spring 1999. A continuum of GS-25 tiller densities was generated no-till fields in the Southeast. Where wheat is planted (161-1774 tillers m Ϫ2 ) by planting at different seeding rates and dates late after soybean [Glycine max (L.) Merr.] or cotton in a randomized complete block design. Five N treatments were ap-(Gossypium hirsutum L.), GS-25 tiller densities can be plied at GS-25, and three were applied at GS-30. Tillering response to early spring N, yield, and yield components were measured. increasing as low as 350 tillers m Ϫ2 . With the rapid adoption of noearly spring N rates resulted in higher tiller densities at GS-30, and till, we believe it is important to develop N management GS-25 tiller density was a significant covariate. With GS-25 tiller systems that optimize tillering and yield. This is espedensities Ͼ550 tillers m Ϫ2 , yields were higher when all N was applied cially true in sandy Coastal Plain soils, which are comat GS-30. In years without spring freezes, wheat with Ͻ550 tillers mon to the wheat-growing regions of the Southeast. m Ϫ2 achieved optimum yields when spring N was applied at GS-25. Thus, our primary objectives were to determine: (i) if Manipulating the timing of spring N application can optimize early N applied at Zadok's GS-25 improves grain yield of nospring tillering and yield component formation. till winter wheat, (ii) if any yield increase was the result of increased spring tillering, and (iii) if there is a critical tiller density above which N application at GS-25 in no-R. Weisz, Dep. Of Crop Sci., North Carolina State Univ., Box 7620, emergence, strips were divided into 12.2-m-long plots by spray-Raleigh, NC 27695-7620; C.R. Crozier, Dep.

Nitrogen limits crop production when insufficient and harms the environment when excessive. Tailoring N inputs to cropping systems remains a high priority to achieve production and environmental goals. We collected soils from 47 corn (Zea mays L.) production fields in North Carolina and Virginia at depths of 0 to 10, 10 to 20, and 20 to 30 cm and evaluated soil C and N characteristics in association with soil N mineralization. Soil organic C at a depth of 0 to 10 cm varied among sites from ~10 to 80 g kg -1 , and generally declined with depth because of many sites with no-tillage management. N itrogen (N) is considered the most limiting nutrient in plant production. In many cases, demand for N by highly productive crops far exceeds the N that can be supplied by soil. Sources of N from soil are residual inorganic N from previous cropping or organic forms of N in soil organic matter and plant and animal residues, which must be mineralized in synchrony with decomposition processes. Insufficient N leads to low biomass production as a result of limited protein synthesis and low photosynthetic activity, all of which causes cascading negative effects on water-use efficiency, biological activity, ecosystem functioning, economic return from farm capital investment, and social welfare of farming communities (Smil, 2002;Tilman et al., 2011). In contrast, excessive N leads to susceptibility of crops to invasion by pests, leakage of N from the soil and plant systems to the environment causing air and water pollution, and loss of investment from costly inorganic N inputs (Vitousek et al., 1997;Hatfield and Follett, 2008).Nitrogen availability in soils has been investigated for decades (Waksman and Starkey, 1924;Fribourg and Bartholomew, 1956;Stanford, 1968;Jenkinson and Powlson, 1976;Jansson and Persson, 1982;Campbell et al., 1991), yet reliable predictions of N fertilizer application rate to optimize cereal grain yields have been elusive (Balkcom et al., 2003). Early investigations to optimize inorganic N inputs focused on defining potentially mineralizable N from a nonlinear function derived from inorganic N released through successive leaching and incubation (Stanford and Smith, 1972). This methodology has been considered the best estimate of soil N mineralization potential, despite (i) the long time period for evaluation (32 wk Core Ideas• Soil nitrogen mineralization can be predicted with the flush of CO 2 .• Soil texture does not alter the relationship between the flush of CO 2 and N mineralization.• Large quantity of mineralizable N in surface soils is possible with conservation management.• The flush of CO 2 is an appropriate indicator for soil-test biological activity.• The flush of CO 2 is a rapid and reliable indicator of soil N availability.