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Yingchao Lin, Dejun Kong, Zhihong Wang, Yi Chen, Zhixiao Yang, Chun Wu, Hui Yang, and Lili Chen

nitrogen use efficiency and serious N loss, which in turn lead to polluting the environment via emission of greenhouse gases and leaching of nitrate into groundwater ( Campiglia et al., 2011 ; Jensen and Hauggaard-Nielsen, 2003 ; Shi and Yu, 2008 ). Thus

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L. Carolina Medina, Thomas A. Obreza, Jerry B. Sartain, and Robert E. Rouse

Most Florida citrus is grown on extremely sandy soils inherently low in fertility, cation exchange capacity, and ability to retain applied plant nutrients. Traditionally, the main way of providing nitrogen (N) to Florida citrus trees has been

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Xiaofeng Yang, Gang Li, Weihong Luo, Lili Chen, Shaopeng Li, Ming Cao, and Xuebin Zhang

Muskmelon ( Cucumis melo L.) is one of the most important high-value crops in protective cultivation. In China, the planting area of muskmelon was 42 × 10 4 ha with the fruit yield exceeded 1400 × 10 7 kg in 2013. Nitrogen plays an important role

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M. Murshidul Hoque, Husein Ajwa, Mona Othman, Richard Smith, and Michael Cahn

more than 150 kg nitrogen (N)/ha/crop ( Jackson et al., 1994 ). Similarly, the excessive accumulation of soil phosphorus (P) has raised water quality concerns ( Sims, 1998 ). Salinas Valley soils often contain more than 30 to 40 mg·kg −1 of bicarbonate

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Tim R. Pannkuk, Jacqueline A. Aitkenhead-Peterson, Kurt Steinke, James C. Thomas, David R. Chalmers, and Richard H. White

Excessive losses of nitrogen (N), orthophosphate (P), and DOC from soil by leaching is indicative of breaks in their respective nutrient cycles. Losses of these nutrients are typically caused by management practices or natural disturbances in the

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Benjamin Wherley and Thomas R. Sinclair

Nitrogen (N) is the nutrient used in greatest quantity by plants and, consequently, is the element around which most turfgrass fertility programs are centered. Nitrogen is a component of many of the biochemical constituents of plants, including

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Brent L. Black, Stan C. Hokanson, and Kim S. Lewers

In the perennial strawberry production system, removal of the harvested crop represents a loss of nitrogen (N) that may be influenced by cultivar. Eight strawberry (Fragaria ×ananassa Duch.) cultivars and eight numbered selections grown in advanced matted row culture were compared over three seasons for removal of N in the harvested crop. Replicated plots were established in 1999, 2000, and 2001 and fruited the following year. `Allstar', `Cavendish', `Earliglow', `Honeoye', `Jewel', `Northeaster', `Ovation', and `Latestar' and selections B37, B51, B244-89, B683, B753, B781, B793, and B817 were compared for yield and fruit N concentration. Harvest removal of N (HRN) was calculated from total season yield and fruit N concentration at peak harvest. There were significant differences in HRN among genotypes, ranging from 1.80 to 2.96 g N per meter of row for numbered selections B781 and B37, respectively. Among cultivars, HRN ranged from 2.01 to 3.56 g·m–1 for `Ovation' and `Jewel', respectively. The amount of HRN was largely determined by yield, however, there were also significant genotype differences in fruit N concentration, ranging from 0.608 to 0.938 mg N per gram fresh weight for B244-89 and `Jewel', respectively. These differences indicate that N losses in the harvested crop are genotype dependent.

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Wendy A. Johnson, Raymond A. Cloyd, James R. Nechols, Kimberly A. Williams, Nathan O. Nelson, Dorith Rotenberg, and Megan M. Kennelly

Nitrogen (N) is an essential nutrient that crops require for growth and development ( Jones, 1998 ; Raven and Smith, 1976 ). The availability and form of N may vary depending on fertilizer type. Organic fertilizers, which are derived from natural

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Paula B. Aguirre, Yahya K. Al-Hinai, Teryl R. Roper, and Armand R. Krueger

Nitrogen (N) uptake was compared on 10 dwarf apple rootstocks (M.9 EMLA, M.26 EMLA, M.27 EMLA, M.9 RN29, Pajam 1, Pajam 2, B.9, Mark, B.469, and M.9 T337) grafted with the same scion (`Gala') in a four year-old orchard. Trees were treated in either Spring or Fall 1998 with 40 g of soil applied actual N per tree using ammonium nitrate enriched to 1% 15N. Both percentage of N (%N) and N from fertilizer (NFF) in leaf tissue were highly affected by the rootstock and the season of N application. Generally, higher %N and NFF were observed for spring than fall applications, except for leaves collected during early June 1998. Generally, M.26 EMLA, M.27 EMLA, and M.9 RN29 were the most efficient rootstocks in N uptake for spring applied nitrogen. M.9 EMLA was most efficient late in the season following fall application. Mark was more efficient early in the season for fall applied N than spring application. However, trees on Mark rootstock had the lowest %N throughout the season regardless of the time of N application. Pajam 1 and Pajam 2 were the least efficient rootstocks in N uptake following fall N application. Rootstock also significantly affected %N and NFF of wood tissue. Generally, trees on B.469 had the highest %N in their wood regardless of the season of application. No single rootstock had consistently higher N from fertilizer in their wood tissue after spring application. At the May 1999 sampling date, M.26 EMLA had higher NFF than M.27 EMLA, Pajam 1, Pajam 2, and B.9 with a fall application. Other rootstocks were intermediate. Samples collected in August showed that Pajam 1 was the least efficient rootstock in N uptake for fall applied N compared to other rootstocks, except for Pajam 2 and B.9 that were intermediate. Leaf and wood tissue analysis showed that different rootstocks had different N uptake efficiencies throughout the season. Generally, M.26 EMLA, M.27 EMLA, M.9 RN29 and M.9 EMLA were more efficient at N uptake regardless the season of N application. Pajam 1 and Pajam 2 were the least efficient.

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A. Bar-Tal, B. Aloni, L. Karni, and R. Rosenberg

The objective of this research was to study the effects of N concentration and N-NO3: N-NH4 ratio in the nutrient solution on growth, transpiration, and nutrient uptake of greenhouse-grown pepper in a Mediterranean climate. The experiment included five total N levels (0.25 to 14 mmol·L-1, with a constant N-NO3: N-NH4 ratio of 4) and five treatments of different N-NO3: N-NH4 ratios (0.25 to 4, with a constant N concentration of 7 mmol·L-1). Plants were grown in an aero-hydroponic system in a climate-controlled greenhouse. The optimum N concentrations for maximum stem and leaf dry matter (DM) production were in the range of 8.0 to 9.2 mmol·L-1. The optimum N-NO3: N-NH4 ratio for maximal stem DM production was 3.5. The optimum value of N concentration for total fruit DM production was 9.4 mmol·L-1. Fruit DM production increased linearly with increasing N-NO3: N-NH4 ratio in the range studied. The N concentration, but not N source, affected leaf chlorophyll content. Shorter plants with more compacted canopies were obtained as the N-NO3: N-NH4 ratio decreased. The effect of N concentration on transpiration was related to its effect on leaf weight and area, whereas the effect of a decreasing N-NO3: N-NH4 ratio in reducing transpiration probably resulted from the compacted canopy. Nitrogen uptake increased as the N concentration in the solution increased. Decreasing the N-NO3: N-NH4 ratio increased the N uptake, but sharply decreased the uptake of cations, especially Ca.