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No abstract

Rising concerns about greenhouse gases, increased fuel prices, and the potential for new high value agricultural products have raised interest in the use of maize stover for bioenergy production. However, residue harvest must be weighed against potential negative impacts on soil quality. This study, conducted in Chazy, NY, evaluated the long‐term effects of 32 yr of maize (Zea mays L.) stover harvest vs. stover return on soil quality in the surface layer (5–66 mm) under plow till (PT) and no‐till (NT) systems on a Raynham silt loam (coarse‐silty, mixed, active, nonacid, mesic Aeric Epiaquept) using physical, chemical, and biological soil properties as soil quality indicators. Twenty‐five soil properties were measured, including standard chemical soil tests, aggregate stability (WSA), bulk density, (ρb) penetration resistance (PR), saturated hydraulic conductivity (Ks), infiltrability (Infilt), several porosity indicators (aeration pores(PO > 1000), soil water potential = Ψ > −0.36 kPa; air‐filled pores at field capacity (PO > 30), Ψ > −10kPa; available water capacity (AWC), −1500 < Ψ < −10 kPa), total organic matter (OM), parasitic (Nemparasitic) and beneficial nematode (Nem beneficial) populations, decomposition rate (Decomp), potentially mineralizable N (PMN) and easily extractable (EEG) and total glomalin (TG). Only eight indicators were adversely affected by stover harvest, and most of these effects were significant only under NT. Almost all indicators affected by stover removal were affected equally or more adversely by tillage. A total of 15 indicators were adversely affected by tillage. Results of this study suggest that, on a silt loam soil in a temperate climate, long‐term stover harvest had lower adverse impacts on soil quality than long‐term tillage. Stover harvest appears to be sustainable when practiced under NT management.

We evaluated spring phenology changes from 1965 to 2001 in northeastern USA utilizing a unique data set from 72 locations with genetically identical lilac plants (Syringa chinensis, clone "Red Rothomagensis"). We also utilized a previously validated lilac-honeysuckle "spring index" model to reconstruct a more complete record of first leaf date (FLD) and first flower date (FFD) for the region from historical weather data. In addition, we examined mid-bloom dates for apple (Malus domestica) and grape (Vitis vinifera) collected at several sites in the region during approximately the same time period. Almost all lilac sites with significant linear trends for FLD or FFD versus year had negative slopes (advanced development). Regression analysis of pooled data for the 72 sites indicated an advance of -0.092 day/year for FFD (P=0.003). The slope for FLD was also negative (-0.048 day/year), but not significant (P=0.234). The simulated data from the "spring index" model, which relies on local daily temperature records, indicated highly significant (P<0.001) negative slopes of -0.210 and -0.123 day/year for FLD and FFD, respectively. Data collected for apple and grape also indicated advance spring development, with slopes for mid-bloom date versus year of -0.20 day/year (P=0.01) and -0.146 (P=0.14), respectively. Collectively, these results indicate an advance in spring phenology ranging from 2 to 8 days for these woody perennials in northeastern USA for the period 1965 to 2001, qualitatively consistent with a warming trend, and consistent with phenology shifts reported for other mid- and high-latitude regions.

Stress‐induced senescence is frequently alluded to, but interactive effects of water and N deficits on leaf longevity and on physiological changes associated with leaf aging have received little attention. A 2‐yr field experiment with maize (Zea mays L.) was conducted on Yolo loam (fine‐silty, mixed, nonacid, thermic Typic Xerorthents) with four treatments: N fertilized (180 kg N/ha) with (NI) and without (ND) irrigation; and no N applied with (OI) and without (OD) irrigation. Size and longevity measurements were made of leaves at all nodal positions, and leaves 5, 11, and 15 (counting up from stem base) were monitored for changes in photosynthetic capacity (PC), N concentration, and chlorophyll content (CHL). Leaf PC was correlated with percent N during senescence in all treatments (r2 = 0.86), but an occasional midday depression in PC, unrelated to leaf N status, was observed in severely water stressed plants. Chlorophyll and percent N were also correlated (r2 = 0.80), but initial onsets of decline in these two parameters often differed by several days. Nitrogen deficits were less severe in 1983 than 1982, but in both years lack of applied N had an early impact and reduced longevity of lower leaves. In 1982, N deficiency caused a 50% reduction in leaf peak values of percent N, CHL, and PC, and the decline in leaf 5 was most rapid in low N plants. Water stress intensified as stored soil water was gradually depleted, and the most rapid decline and earliest complete senescence of upper leaves (11 and 15) occurred in the ND treatment. These results indicate that early stress effects on leaf area and ear development affected subsequent demands for water and N, which in turn altered patterns of leaf senescence.