Ecosystem-based approaches to nutrient management are needed to satisfy crop nutrient requirements while minimizing environmental impacts of fertilizer use. Applying crop residues as soil amendments can provide essential crop nutrient inputs from organic sources while improving nutrient retention, soil health, water conservation, and crop performance. Tree crop hulls, husks, and shells have been found to contain high concentrations of potassium across species including almond, cacao, coffee, pecan, and hazelnut. The objective of this review is to characterize organic sources of potassium focusing on lignocellulosic pericarps and discuss reported effects of surface application on potassium cycling, water dynamics, soil functionality, and crop yield. Research indicates potassium ions solubilize readily from plant material into soil solution due to potassium’s high mobility as a predominately unbound monatomic cation in plant tissues. Studies evaluating tree crop nutshells, field crop residues, and forest ecosystem litter layers indicate this process of potassium release is driven primarily by water and is not strongly limited by decomposition. Research suggests orchard floor management practices can be tailored to maximize the soil and plant benefits provided by this practice. Contextual factors influencing practice adoption and areas for future study are discussed.

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Smallholder coffee producers are the foundation of the specialty coffee industry and are currently facing a set of challenges that threaten the sustainability of the industry. Movement towards a more sustainable specialty coffee sector requires strong collaboration between interdisciplinary researchers and industry stakeholders to develop research projects and interventions that address critical social, economic, and environmental threats to the industry. To improve upon past sector initiatives it is essential that cross-sector collaboration better incorporate and center coffee farmers’ voices, which have often been absent from top-down interventions. This article describes one such collaboration, which investigated agronomic and market system needs of the Guatemalan smallholder coffee sector. We conducted participatory interviews with 33 coffee producers and 22 non-producer key informants, and used mixed-methods analysis of the interview data to better understand the key challenges facing smallholder coffee producers in Guatemala. The following factors emerged: pests and diseases, climate change, price, labor, nutrient management, market access, yield, nurseries and transplants, and technical assistance. Cross-sector, interdisciplinary collaborations that directly address these areas would directly improve the long-term sustainability of the coffee industry by reducing pressures currently limiting specialty coffee production. This research framework can also serve as a model for others interested in conducting interdisciplinary, cross-sector research.

Heirloom tomato (Solanum lycopersicum L.) are a high-value crop for organic vegetable growers. Tomato plants have a high N requirement and are adversely affected by insufficient, excessive, and poorly timed N fertilization. However, little information is available about N dynamics in heirloom tomato and whether their nutritional needs differ from those of hybrid fresh-market (HFM) tomato. The project's goals were to (a) develop seasonal N accumulation curves for the popular heirloom tomato cultivar Brandywine, (b) measure the N removed with the harvested fruits, and (c) determine whether N concentrations from recently matured leaves from adequately and underfertilized fields as well as N accumulation and partitioning fell within published thresholds for HFM tomato plants. We tracked the leaf N concentrations, growth, yields and N accumulation of organically grown Brandywine tomato in a 2-yr replicated field trial under low-and high-N availability treatments. We also collected leaf and fruit samples from fertilized and unfertilized plots on local commercial organic fields. Total N accumulation ranged between 25 to 45 g N per linear bed meter and did not differ with N treatment. The N removed with the harvested fruit averaged 1.14 kg Mg −1 fresh fruit across all sites and years and differed by site but not N fertility. On average, 70-80% of tomato N demand occurred between full bloom and early harvest. The observed N accumulation per unit yield, seasonal N accumulation pattern, and leaf sufficiency thresholds for Brandywine tomato were within the ranges published for HFM tomato varieties. INTRODUCTIONHeirloom tomato (Solanum lycopersicum, L.) can be one of the most profitable crops for California organic vegetable growers, but they also are expensive to grow and are subject to stringent aesthetic quality standards. Tomato yields and quality are known to be affected by the amount and timing of N fertilization (Scholberg, McNeal, Jones, et al.