Bryan G. Hopkins

Enhanced Efficiency Fertilizers for Improved Nutrient Management: Potato ( Solanum tuberosum )

The improvement of fertilizer efficiency is driven by narrow profit margins, environmental concerns, and resource conservation. Fertile soil is the foundation for food production and successful civilizations; it is developed and maintained through the addition of nutrients lost through harvest. However, nutrient uptake by plants is inherently inefficient and the nutrients remaining in the soil after uptake can cause negative air and water resource impacts. In addition, poor fertilizer efficiency is a waste of natural resources and potentially reduces yields, crop quality, and grower profits. Enhancing fertilizer efficiency in potato is particularly important because relatively high rates of fertilizer and water are necessary to compensate for an inefficient rooting system and extreme sensitivity to deficiencies. Several new fertilizer materials have been designed to enhance fertilizer efficiency. The modes of action of these materials include: (i) slow or controlled release to meet plant need in a more timely fashion; (ii) addition of high charge-density materials that isolate nutrients from interfering elements and compounds; (iii) complexation or chelation of the nutrient to enhance solubility; and (iv) modification of the micro-site pH to enhance nutrient solubility.

Plant utilization of iron solubilized by oat phytosiderophore

Abstract Responses to Fe‐deficiency stress have been classified as Strategies I and II. “Iron‐efficient”; cultivare within each strategy exhibit one or more of a combination of specific physiological responses to Fe‐deficiency stress, while “Fe‐inefficient”; cultivars do not. Iron‐efficient Coker 227 oat (Avena byzantina C. Koch.) is a Strategy II plant which produces an Fe‐chelating compound (phytosiderophore) in response to Fe‐deficiency stress. The objective of this paper is to summarize the results of studies in which the abilities of several plant species to utilize Fe solubilized by oat phytosiderophore were determined. Experiments were conducted in which Fe‐deficiency stressed oat plants were grown in hydroponic solutions (1.2 mg Fe L‐1 unchelated) in combination with three different species of both monocotyledonous and dicotyledonous plants which represented a wide range of Fe‐efficiency. The cultivars varied in response to the oat phytosiderophore as follows: (a) WF9 maize (Zea mays L.), TAM 0–31...

PHOSPHORUS AND MANGANESE INTERACTIONS AND THEIR RELATIONSHIPS WITH ZINC IN CHELATOR-BUFFERED SOLUTION GROWN RUSSET BURBANK POTATO

Manganese (Mn)- and zinc (Zn)-driven antagonistic interactions with high available phosphorus (P) can result in negative impacts on potato cropping systems. Two chelator-buffered hydroponic experiments were conducted with Russet Burbank potato to elucidate P and Mn relationships and associated interactions with Zn. In both experiments, a P concentration decline in new shoots, old shoots, and roots resulted as solution Mn changed from deficient to sufficient followed by a P concentration rise as solution Mn changed to excessive concentrations. New and old shoot Zn concentrations generally increased with augmented solution Mn in the variable Mn experiment, but no significant changes were found in root Zn contents. Available Mn was observed to control plant P concentrations and to influence Zn uptake and translocation; thus, Mn has considerable impact on uptake and distribution of P and Zn and on P-Zn interactions in potato.

Influence of Soil Water Repellency on Seedling Emergence and Plant Survival in a Burned Semi-Arid Woodland

High intensity wildfires in semiarid shrub and woodland plant communities can leave ecosystems incapable of self-repair and susceptible to weed invasion. Subsequently, land managers need effective restoration tools to reseed native vegetation back into these degraded systems. In order to develop successful post-fire restoration approaches in these communities, it is critical that we understand the mechanisms that impair reseeding success. Our objective was to quantify the influence of soil water repellency on seedling emergence and plant growth in a greenhouse study using soil cores obtained from beneath burned Juniperus osteosperma trees. Soil cores were seeded with either Elymus wawawaiensis or Agropyron cristatum, and watered with either a high (watered daily) or a low water regime (watered every 5 days). During the first watering event, water repellency was ameliorated in half the cores by adding a wetting-agent comprised of alkylpolyglycoside-ethylene oxide/propylene oxide block copolymers. Results showed that water repellency reduced seedling emergence and seedling survival by decreasing soil moisture availability. Wetting-agents improved ecohydrologic properties required for plant growth by decreasing runoff and increasing the amount and duration of available water for seedling emergence, survival, and plant growth. These results indicate that soil water repellency can act as an ecological threshold by impairing establishment of reseeded species after a fire. Where restoration efforts are limited by soil water repellency, wetting agents have the potential to improve the success of post-fire reseeding efforts. Future work is needed to validate these findings in the field.

PHOSPHORUS AND ZINC INTERACTIONS IN CHELATOR-BUFFERED SOLUTION GROWN RUSSET BURBANK POTATO

High phosphorus (P) application in potato production potentially leads to antagonistic interactions with cationic micronutrients. None of the nine combinations of phosphorus and zinc (Zn) provided in chelator-buffer solution for 17 days to potato supported the concept of a P-induced Zn deficiency with regard to early season dry matter yield, especially when solution P ranged from sufficient to excessive—conditions under which P-Zn interaction traditionally is observed. Increased solution P at low Zn levels resulted in a steep increase of P in new and old shoot growth and an accumulation of manganese (Mn) in potato roots—a combination that might indirectly impact Zn nutrition in potato. Although high P levels in potato did not directly reduce Zn content or cause Zn deficiency, excessive P accumulation may reduce the activity of Zn by interacting with other micronutrients such as Mn.

Evaluation of potato production best management practices

A 2001 survey indicated that many growers are reluctant to adopt research-based recommendations because of a perception that it is not practical or applicable to their specific farming operation. Other growers, however, appear to adopt these practices successfully. Highlighting “model” growers is a method that can be used to field-test research findings and facilitate grower adoption. The objectives of this project were to: 1) establish field demonstrations with potato (Solariumtuberosum L.) growers who generally follow researchbased best management practices (BMPs); 2) establish plots within each field to compare BMPs with a high input, maximum yield management (MYM) approach; and 3) enhance grower confidence regarding researchbased BMPs. Fourteen field trials were conducted in the Pacific Northwest during 2002-2005. Five replicates of BMP and MYM plots were established in each field. The BMPs consisted of sampling, scouting, and use of prediction models to aid in determining rate and timing of inputs to maximize returns. In contrast, the MYM approach was based on tradition and calendar timing, with a near zero tolerance for pest and nutrient limitations. The MYM plots had 1.7 to 13.2% more fertilizer and pesticide costs than the BMP plots. The MYM treatments resulted in significant marketable yield increases in three fields and decreases in two fields, with the remaining nine fields and the combined average of all 14 fields being statistically equivalent. When factoring in estimated costs, only two fields resulted in a monetary advantage with MYM treatment. In contrast, the BMP treatment resulted in significant increases in net crop value in five fields, as well as the combined average of all 14 fields (

PHOSPHORUS AND ZINC INTERACTIONS AND THEIR RELATIONSHIPS WITH OTHER NUTRIENTS IN MAIZE GROWN IN CHELATOR-BUFFERED NUTRIENT SOLUTION

200 ha-1 or 3.2%). These field demonstrations, along with associated field days and grower meetings, have resulted in many documented changes in grower practices towards BMPs, with many more undocumented changes probable.ResumenUn estudio que se hizo el 2001 indica que muchos agricultores son renuentes a adoptar las recomendaciones basadas en la investigación, debido a una percepción poco práctica o aplicable a sus operaciones de cultivo. Otros, sin embargo, parecen adoptar exitosamente estas prácticas. El destacar a los agricultores “modelo” es un método que pude ser usado para probar en el campo los resultados de la investigación y facilitar su adopción. Los objetivos de este proyecto fueron: 1) hacer demostraciones de campo con los agricultores que cultivan papa (Solarium tuberosum L.) que emplean generalmente las mejores prácticas de mane jo (BMPs) basadas en investigación; 2) establecimiento de parcelas dentro de cada campo las BMPs con gastos altos, un enfoque de manejo máximo de rendimiento (MYM); 3) incremento de la confianza del agricultor referida a los BMPs basados en investigación. Catorce pruebas de campo se realizaron el Pacñfico Nor Occidental durante 2002-2005. Cinco repeticiones de BMP y de MYM se hicieron por parcela en cada campo. Los BMPs consistieron de muestreos, exploración y uso de modelos de predicción para ayudar a determinar la tasa y registro de gastos para alcanzar el máximo de ganancia. Contrariamente, el enfoque MYM estuvo basado en la tradición y distributión del tiempo, con tolerancia cero para problemas de pestes y nutrientes. Las parcelas MYM recibieron 1.7 a 13.2% de gastos en fertilizantes y pesticidas que las parcelas BMP. Los tratamientos resultaron en aumento significativo de rendimiento comerciable en tres campos disminución con los restantes nueve y el promedio combinado de los 14 campos estadñsticamente equivalentes. Cuando se factorizó en gastos estimados, sólo dos campos resultaron en ventaja monetaria con el tratamiento MYM. Contrariamente, el tratamiento BMP dio como resultado un incremento significativo en cinco campos, asñ como el promedio combinado de todos los 14 campos (

PHOSPHORUS FERTILIZER TIMING FOR RUSSET BURBANK POTATO GROWN IN CALCAREOUS SOIL

200 ha-1 o 3.2%). Estas demostraciones de campo, junto con los asociados dñas de campo y reuniones de agricultores, han dado como resultado muchos cambios documentados en el proceder de los agricultores hacia los BMPs, con cambios probables no documentados.

Improving Phosphorus Use Efficiency Through Potato Rhizosphere Modification and Extension

Maize (Zea mays L.) is common in potato (Solanum tuberosum L.) cropping systems and is especially susceptible to zinc (Zn) deficiency, possibly related to induced potato demand for high phosphorus (P). Three chelator-buffered nutrient solution experiments were evaluated for maize response to establish ranges of deficient, sufficient, and excessive Zn and P and to evaluate interactions. Zinc concentrated in roots and manganese (Mn) accumulated in shoots as P increased, but only 32 μM P produced significantly lower shoot Zn than other treatments and there was not a decline in shoot Zn at high P levels. Deficient Zn levels promoted excessive P uptake. Root Mn increased dramatically above 0.05 μM Zn, peaked at 20 and 40 μM Zn, and then declined at higher solution Zn levels. The P-Zn interaction in maize may be explained by the combined impacts of increased available P on Zn precipitation in roots and increased Mn in shoots.

OPTIMIZING PHOSPHORUS AND ZINC CONCENTRATIONS IN HYDROPONIC CHELATOR-BUFFERED NUTRIENT SOLUTION FOR RUSSET BURBANK POTATO

Potato (Solanum tuberosum L.) has surface roots with enhanced activity upon canopy closure that should allow application of phosphorus (P) via fertigation. Fertilizer trials were conducted in 2005–2006 with four pre-plant broadcast (0, 112, 224, or 336 kg P2O5 ha−1) and two split applied in-season fertigation (0 or 56 kg P2O5 ha−1) rates. Total and undersized tuber yield had a quadratic relationship with pre-plant P, increasing and then declining as pre-plant P fertilizer rate increased, with predicted yield peaks at 246 and 167 kg P2O5 ha−1, respectively. Marketable and US No. 1 yields increased linearly with increasing pre-plant P fertilizer rate. A trend for an increase in total yield as a function of in-season P fertilization was also measured. The P rate for maximum yield did not decline with in-season application, suggesting that this practice does not enhance P fertilizer use efficiency.