Efficient N fertilizer management is crucial for ensuring maximum economic production and improving N recovery efficiency ( Guan et al., 2011 ; Zhang et al., 2013 ). To increase root yield of the radish, excessive N fertilizers are applied in the
Nitrate concentrations in the springs and rivers in northern Florida have been increasing, and several state agencies are interested in implementing nitrogen management programs on farms to reduce N entering the groundwater. Watermelon was grown in the first season of a six-season project under various cultural and fertilization programs to investigate the relationship of N management with N leaching. Treatments were a factorial arrangement of two cultural systems (polyethylene mulch with drip-irrigated beds and unmulched, overhead irrigated beds) and three N fertilization programs [N at the extension-recommended rate, N at the commercial-watermelon-producer rate (1.5 times recommended), or N at the recommended rate with 50% of N from poultry manure]. Nitrate in the soil beneath the watermelon crop was monitored at the 2-m depth with porous-crop suction lysimeters and soil sampling. Yields were greater with the mulch/drip irrigation system compared with the unmulched/sprinkler cultural system; however, fertilization program had no effect on yield. Nitrate-N concentrations in the soil solution at the 2-m depth with all fertilizer treatments were only slightly elevated (3 to 5 mg·L-1) above that in the unfertilized soil (< 1.0 mg·L-1) early in the season when no rain fell. Later in the season, soil solution nitrate-N concentrations at the 2-m depth increased to >50 mg·L -1 with the unmulched treatment and with the greater fertilization rate. Polyethylene mulch, drip irrigation, and recommended N rate combined to maintain groundwater nitrate-N concentration below 10 mg·L-1 for most of the production season and only slightly above 10 mg·L-1 during the summer off-season when rainfall was frequent.
Commercial apple (Malus domestica Borkh.) orchards in the northeastern United States receive heavy pesticide inputs and are often located on well-drained soils near surface and groundwater resources. Nonpoint-source water pollution by agrichemicals has been monitored in agronomic crop systems and simulated using computer models and laboratory soil columns, but inadequately studied at field scale in orchards. We monitored the concentrations of agrichemical tracers, nitrate-N, and benomyl fungicide in water samples from two apple orchards under mowed sodgrass (Mowed-Sod), shredded bark mulch (Bark-Mulch), preemergence residual herbicides (Resid-Herb), and postemergence herbicide (Post-Herb) groundcover management systems (GMSs). In one orchard, we evaluated subsurface spatial patterns and flow rates of a weakly adsorbed blue dye (pesticide analog) and potassium bromide (nitrate analog) under trees after six years of Post-Herb and Mowed-Sod treatments. Nitrate and pesticide tracers leached more rapidly and in higher concentrations under Post-Herb treatments, apparently via preferential macropore flowpaths such as root channels, soil cracks, and macrofauna burrows. At another orchard, we monitored subsurface leaching and surface runoff of benomyl and nitrate-N on a whole-field scale. Peak concentrations of benomyl (up to 29 mg·liter-1) and nitrates (up to 20 mg·liter-1) were observed in subsoil leachate under Resid-Herb plots during 1993. In 1994, nitrate concentrations were greater in leachate from all GMSs, with upper ranges from 48 to 66 mg·liter-1, while benomyl concentrations were lower in all GMSs compared with the previous summer. In surface water runoff during 1993, the highest benomyl concentrations (387 mg·liter-1) and most frequent outflows occurred in Resid-Herb plots. During 1994, benomyl runoff was more frequent in both herbicide GMSs, with concentrations up to 61 mg·liter-1 observed in the Post-Herb plots. Weather patterns, irrigation intensity, differing soil conditions under each GMS, and the turfgrass/clover drive lanes affected the relative frequency and concentrations of benomyl and nitrate leaching and runoff. Preferential bypass flow appeared to be a major subsurface leaching pathway, and erosion sediment an important factor in surface movement of these agrichemicals. Our studies suggest that nitrate-N and benomyl fungicide may be more prone to leaching or runoff from orchard soils under some herbicide GMSs in comparison with mowed sodgrass or biomass mulch systems.
Changes in the soil total nitrogen (N) pool occur slowly in response to changing management practices. Due to its large size and inherent spatial variability, only a small fraction of the soil total N pool is available to plants ( Zhang et al., 2016
in high N demand crops such as tomato ( Gaskell and Smith, 2007 ). Not only must organic soil management provide sufficient plant-available N to maximize crop productivity, but also do so in a timely manner to ensure that crops are not N limited at
building enzymes, chlorophyll, and other important compounds in plants ( Marschner, 2012 ). Effective N management can reduce inputs and minimize N losses to the environment, but requires a thorough understanding of plant nutrient demand in terms of amount
Soil fertility management is an important and costly cultural practice for organic vegetable growers. Nitrogen (N) is often the most limiting nutrient to efficient and profitable vegetable production and at the same time, N losses and inefficient N
and spatial arrangement of plants ( Shapiro and Wortmann, 2006 ), N fertilization rate and application methods (for both placement and timing) ( Li, 2003 ; Linaje et al., 2005 ; Ma and Kalb, 2006 ; Osborne, 2006 ), water management, and concurrent
large scale. Nitrogen management in large-scale production is a challenge to growers, particularly for crops such as sweet corn that require large amounts of N for optimal production (150 lb/acre) ( Laboski et al., 2006 ). Nitrogen can be a costly input
N immobilization, and soil or groundcover management ( Haynes, 1988 ; Merwin, 2003a ; Merwin et al., 1996 ). A seasonal pattern of nitrate-N losses through leaching has been observed in fertilized orchards with higher N losses during times of year