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Robert L. Mikkelsen

illustration of the 4R framework for fertilizer best management practices. Selecting the right nutrient source, applied at the right rate, right time, and right place, helps to achieve crop management objectives of productivity, profitability, sustainability

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Bielinski M. Santos

management for crops, which are defined as the “4R” nutrient management concept: “rightrate, source, placement, and timing ( Bruulsema et al., 2009 ; Roberts, 2007 ). Therefore, the objective of this paper was to provide general principles for selecting

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Mark Gaskell and Tim Hartz

Nutrient management practices must be tailored to the crop, environment, and production system if nutrient efficiency and environmental water quality protection are to be achieved. This requires consideration of fertilizer choice, placement, application rate, and timing. These factors have been characterized as the “4Rs” of nutrient stewardship—right material, right placement, right rate, and right timing. The factors affecting the choice of fertilizer material have been described previously for agronomic crops, and include plant nutritional requirements, soil conditions, fertilizer delivery issues, environmental risks, product price, and economic constraints. Although those factors are applicable to all crops, the unique features of intensive horticultural production systems affect their interactions. This article discusses fertilizer choice as it affects productivity, profitability, sustainability, and environmental impact of intensive horticultural crop production. Diverse fertilizer materials are available for specialized application to provide nitrogen, phosphorus, potassium, and other plant nutrients for different horticultural needs. These fertilizer sources can be formulated as dry or liquid blends, but increasingly higher solubility materials are used to target plant growth needs even in field operations. Composts can have useful applications—particularly for certified organic production—but their high cost, bulk, and relatively low efficiency limit their use. Profitability can be affected by fertilizer cost—typically a relative small percentage of overall costs in intensive production systems—and the improved efficiency of these specialized materials often improves profitability. There are also sustainability issues with the manufacture, transport, and efficient use of different fertilizer sources. Such factors as soil chemical reaction changes, effects on soil salinity, and loss of organic matter also can adversely affect sustainability, but systems are available to maintain soil quality while using more efficient fertilizer sources.

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Neil S. Mattson and Marc W. van Iersel

The 4R nutrient stewardship framework presents four concepts to consider when applying fertilizers in a responsible matter; the “right source” of nutrients should be applied at the “right rate” during the “right time” and supplied to the “right place” to ensure their uptake. In this article, we provide ideas to consider when attempting to provide nutrients at the right time. When nutrients are applied at a time when they are not required by the plant, the result can be economic and environmental losses. Oversupply relative to plant demand can result in losses of applied nutrients because of leaching or volatilization. Undersupply relative to demand, especially in the case of phloem-immobile nutrients, may limit plant growth and yield. Several factors interact to affect plant nutrient demand such as growth stage, life history (annual vs. perennial), environmental conditions, and plant health. Techniques such as soil and tissue testing, isotopic labeling, and spectral reflectance have been used with varying degrees of success and expense to measure plant nutrient demand and guide fertilizer decisions. Besides knowledge of plant nutrient demand, efficient nutrient supply also depends on systems that allow precise spatial and temporal delivery of nutrients. Future improvements to the timing of nutrient delivery will depend on improvement in knowledge of plant nutrient demands. For example, targeted gene expression chips show promise for use in rapidly assessing plant status for a broad suite of nutrients. Future developments that allow more precise nutrient delivery or more robust agroecosystems that scavenge available nutrients before they are lost to the environment will also help producers use nutrients more efficiently.

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Robert Conway Hochmuth, Marina Burani-Arouca, and Charles Edward Barrett

attain the 206 kg·ha −1 N rate by using the BMPs associated with the 4-Rs Principles: right rate, right place, right source, and right timing ( FDACS, 2015 ) and when weather related nutrient leaching is not a major factor. In situations where N would be

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Togo Shinohara, Shinsuke Agehara, Kil Sun Yoo, and Daniel I. Leskovar

(left) and nitrogen (right) rates during harvest (early, mid, and late) in the 2005–2006 season (top) and the 2006–2007 (bottom). Vertical bars indicate mean ± se . In the 2006–2007 season, neither irrigation nor N rates affected phenolic content in any

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Ertan Yildirim, Huseyin Karlidag, Metin Turan, Atilla Dursun, and Fahrettin Goktepe

efficiency of applied fertilizers, reducing cost of inputs and preventing loss of nutrients to ecosystems ( Baligar et al., 2001 ). Fertilizer use efficiency can be optimized by fertilizer management practices that apply nutrients at the right rate, time, and

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Gladys A. Andiru, Claudio C. Pasian, Jonathan M. Frantz, and Pablo Jourdan

fertilizer, at the right time, at the right rate, and at the right location. Appropriate application methods and CRF types must be calibrated to match crop production ( Broschat and Klock-Moore, 2001 ). The nursery and greenhouse industries account for ≈20