Robert P. Larkin

Effects of Different 3-Year Cropping Systems on Soil Microbial Communities and Rhizoctonia Diseases of Potato

ABSTRACT Eight different 3-year cropping systems, consisting of soybean-canola, soybean-barley, sweet corn-canola, sweet corn-soybean, green bean-sweet corn, canola-sweet corn, barley-clover, and continuous potato (non-rotation control) followed by potato as the third crop in all systems, were established in replicated field plots with two rotation entry points in Presque Isle, ME, in 1998. Cropping system effects on soil microbial community characteristics based on culturable soil microbial populations, single carbon source substrate utilization (SU) profiles, and whole-soil fatty acid methyl ester (FAME) profiles were evaluated in association with the development of soilborne diseases of potato in the 2000 and 2001 field seasons. Soil populations of culturable bacteria and overall microbial activity were highest following barley, canola, and sweet corn crops, and lowest following continuous potato. The SU profiles derived from BIOLOG ECO plates indicated higher substrate richness and diversity and greater utilization of certain carbohydrates, carboxylic acids, and amino acids associated with barley, canola, and some sweet corn rotations, indicating distinct differences in functional attributes of microbial communities among cropping systems. Soil FAME profiles also demonstrated distinct differences among cropping systems in their relative composition of fatty acid types and classes, representing structural attributes of microbial communities. Fatty acids most responsible for differentiation among cropping systems included 12:0, 16:1 omega5c, 16:1 omega7c, 18:1 omega9c, and 18:2omega6c. Based on FAME biomarkers, barley rotations resulted in higher fungi-to-bacteria ratios, sweet corn resulted in greater mycorrhizae populations, and continuous potato produced the lowest amounts of these and other biomarker traits. Incidence and severity of stem and stolon canker and black scurf of potato, caused by Rhizoctonia solani, were reduced for most rotations relative to the continuous potato control. Potato crops following canola, barley, or sweet corn provided the lowest levels of Rhizoctonia disease and best tuber quality, whereas potato crops following clover or soybean resulted in disease problems in some years. Both rotation crop and cropping sequence were important in shaping the microbial characteristics, soilborne disease, and tuber qualities. Several microbial parameters, including microbial populations and SU and FAME profile characteristics, were correlated with potato disease or yield measurements in one or both harvest years. In this study, we have demonstrated distinctive effects of specific rotation crops and cropping sequences on microbial communities and have begun to relate the implications of these changes to crop health and productivity.

Rotation and Cover Crop Effects on Soilborne Potato Diseases, Tuber Yield, and Soil Microbial Communities

Seven different 2-year rotations, consisting of barley/clover, canola, green bean, millet/rapeseed, soybean, sweet corn, and potato, all followed by potato, were assessed over 10 years (1997-2006) in a long-term cropping system trial for their effects on the development of soilborne potato diseases, tuber yield, and soil microbial communities. These same rotations were also assessed with and without the addition of a fall cover crop of no-tilled winter rye (except for barley/clover, for which underseeded ryegrass was substituted for clover) over a 4-year period. Canola and rapeseed rotations consistently reduced the severity of Rhizoctonia canker, black scurf, and common scab (18 to 38% reduction), and canola rotations resulted in higher tuber yields than continuous potato or barley/clover (6.8 to 8.2% higher). Addition of the winter rye cover crop further reduced black scurf and common scab (average 12.5 and 7.2% reduction, respectively) across all rotations. The combined effect of a canola or rapeseed rotation and winter rye cover crop reduced disease severity by 35 to 41% for black scurf and 20 to 33% for common scab relative to continuous potato with no cover crop. Verticillium wilt became a prominent disease problem only after four full rotation cycles, with high disease levels in all plots; however, incidence was lowest in barley rotations. Barley/clover and rapeseed rotations resulted in the highest soil bacterial populations and microbial activity, and all rotations had distinct effects on soil microbial community characteristics. Addition of a cover crop also resulted in increases in bacterial populations and microbial activity and had significant effects on soil microbial characteristics, in addition to slightly improving tuber yield (4% increase). Thus, in addition to positive effects in reducing erosion and improving soil quality, effective crop rotations in conjunction with planting cover crops can provide improved control of soilborne diseases. However, this study also demonstrated limitations with 2-year rotations in general, because all rotations resulted in increasing levels of common scab and Verticillium wilt over time.

Effects of Different Potato Cropping System Approaches and Water Management on Soilborne Diseases and Soil Microbial Communities

Four different potato cropping systems, designed to address specific management goals of soil conservation, soil improvement, disease suppression, and a status quo standard rotation control, were evaluated for their effects on soilborne diseases of potato and soil microbial community characteristics. The status quo system (SQ) consisted of barley underseeded with red clover followed by potato (2-year). The soil-conserving system (SC) featured an additional year of forage grass and reduced tillage (3-year, barley/timothy-timothy-potato). The soil-improving system (SI) added yearly compost amendments to the SC rotation, and the disease-suppressive system (DS) featured diverse crops with known disease-suppressive capability (3-year, mustard/rapeseed-sudangrass/rye-potato). Each system was also compared with a continuous potato control (PP) and evaluated under both irrigated and nonirrigated conditions. Data collected over three potato seasons following full rotation cycles demonstrated that all rotations reduced stem canker (10 to 50%) relative to PP. The SQ, SC, and DS systems reduced black scurf (18 to 58%) relative to PP; SI reduced scurf under nonirrigated but not irrigated conditions; and scurf was lower in DS than all other systems. The SQ, SC, and DS systems also reduced common scab (15 to 45%), and scab was lower in DS than all other systems. Irrigation increased black scurf and common scab but also resulted in higher yields for most rotations. SI produced the highest yields under nonirrigated conditions, and DS produced high yields and low disease under both irrigation regimes. Each cropping system resulted in distinctive changes in soil microbial community characteristics as represented by microbial populations, substrate utilization, and fatty acid methyl-ester (FAME) profiles. SI tended to increase soil moisture, microbial populations, and activity, as well result in higher proportions of monounsaturated FAMEs and the FAME biomarker for mycorrhizae (16:1 ω6c) relative to most other rotations. DS resulted in moderate microbial populations and activity but higher substrate richness and diversity in substrate utilization profiles. DS also resulted in relatively higher proportions of FAME biomarkers for fungi (18:2 ω6c), actinomycetes, and gram-positive bacteria than most other systems, whereas PP resulted in the lowest microbial populations and activity; substrate richness and diversity; proportions of monounsaturated and polyunsaturated FAME classes; and fungal, mycorrhizae, and actinomycete FAME biomarkers of all cropping systems. Overall, soil water, soil quality, and soilborne diseases were all important factors affecting productivity, and cropping systems addressing these constraints improved production. Cropping system approaches will need to balance these factors to achieve sustainable production and disease management.

The effect of cropping systems and irrigation management on development of potato early blight

Crop and soil management may modify canopy and belowground microclimate, but their effects on potential development and control of early blight are not well documented. Several management systems (Status Quo, Soil Conserving, Soil Improving (SI), Disease Suppressive, and Continuous Potato) were evaluated for their effects on early blight potential under irrigated and rainfed conditions. In 2006 and 2007, microclimatic data at the canopy level were recorded with a data logger. Early blight incidence and severity was determined by visually assessing symptoms. Disease incidence and lesion numbers varied among cropping systems and between years. Disease incidence ranged from 31 to 64% (2006) and 12 to 43% (2007), and was significantly higher with the Continuous Potato system than with Disease Suppressive, Status Quo, Soil Conserving, and SI systems. The relationships of incidence and disease severity with microclimate varied and were mostly non-significant, suggesting that the chosen variables were not reflective of pathogen development. Incidence was significantly associated with cropping systems. Disease prediction based on the Tom-Cast model was not correlated with observed disease levels. This research demonstrated that early blight disease is enhanced through continuous potato production.

Links among Nitrification, Nitrifier Communities, and Edaphic Properties in Contrasting Soils Receiving Dairy Slurry

Soil biotic and abiotic factors strongly influence nitrogen (N) availability and increases in nitrification rates associated with the application of manure. In this study, we examine the effects of edaphic properties and a dairy (Bos taurus) slurry amendment on N availability, nitrification rates and nitrifier communities. Soils of variable texture and clay mineralogy were collected from six USDA-ARS research sites and incubated for 28 d with and without dairy slurry applied at a rate of ~300 kg N ha(-1). Periodically, subsamples were removed for analyses of 2 M KCl extractable N and nitrification potential, as well as gene copy numbers of ammonia-oxidizing bacteria (AOB) and archaea (AOA). Spearman coefficients for nitrification potentials and AOB copy number were positively correlated with total soil C, total soil N, cation exchange capacity, and clay mineralogy in treatments with and without slurry application. Our data show that the quantity and type of clay minerals present in a soil affect nitrifier populations, nitrification rates, and the release of inorganic N. Nitrogen mineralization, nitrification potentials, and edaphic properties were positively correlated with AOB gene copy numbers. On average, AOA gene copy numbers were an order of magnitude lower than those of AOB across the six soils and did not increase with slurry application. Our research suggests that the two nitrifier communities overlap but have different optimum environmental conditions for growth and activity that are partly determined by the interaction of manure-derived ammonium with soil properties.

Delayed Tillage and Cover Crop Effects in Potato Systems

Delayed tillage and the inclusion of cover crops can substantially reduce erosion in intensively tilled potato systems. Both of these practices can potentially impact potato (Solanum tuberosum L.) yield and quality via changes in soil temperature and soil water status, and suppression or enhancement of soil-borne diseases. Research was conducted over six rotation cycles at two Maine locations to evaluate the effects of timing of primary tillage (fall vs. spring) and cover crop [none, red clover (Trifolium pratense L.), ryegrass (Lolium perenne L.), or winter rapeseed (Brassica napus L.)] on grain yield, ground cover, and tuber yield and quality within the context of 2-year barley (Hordeum vulgare L.)]–potato rotations. Delaying primary tillage until spring, immediately before planting potato, resulted in higher soil water content early in the growing season (before or immediately after planting) in some rotation cycles, and also provided nearly complete ground cover during potentially erosive periods in fall and early spring. The inclusion of clover or ryegrass cover crops had small, positive effects on the proportion of the soil surface covered by crop residue (determined by the line intercept method) in both tillage systems. A significant tillage effect on total tuber yield was seen in only one rotation cycle, when delaying tillage until spring reduced yield by about 12%. Cover crop treatments had no effect on total tuber yield, and neither tillage or cover crop affected the proportion of marketable tubers. Tillage did not affect black scurf (Rhizoctonia solani Kühn) and common scab [Streptomyces scabiei (Thaxter) Lambert & Loria], which were significantly reduced by red clover in some rotation cycles. This research shows that conservation practices can be implemented, including delaying primary tillage until spring and including underseeded cover crops during the grain phase of the rotation, while maintaining potato yield.ResumenLa labranza tardía y la inclusión de cultivos de cobertura pueden reducir sustancialmente la erosión en sistemas de labranza intensiva. Ambas prácticas pueden potencialmente afectar el rendimiento y calidad de la papa (Solanum tuberosum L.) por medio de cambios en la temperatura y estado hídrico del suelo, y supresión o intensificación de enfermedades trasmitidas por el suelo. Se realizó la investigación en dos localidades de Maine durante seis ciclos de rotación para evaluar el momento (otoño vs. primavera) de la labranza principal y cultivos de cobertura [(ninguno, trébol rojo (Trifolium pratense L.), ballico (Lolium perenne L.) o colza de invierno (Brassica napus L.)] sobre el rendimiento de granos, cobertura, y rendimiento de tubérculos y calidad en el contexto de dos años de rotación de cebada (Hordeum vulgare L.)–papa. El retrasar la labranza principal hasta la primavera, inmediatamente antes de sembrar papa, dio como resultado un contenido más alto de agua al inicio de la temporada de cultivo (antes o inmediatamente después de la siembra) en ciertos ciclos de rotación, y también proporcionó una cobertura casi completa durante los periodos potencialmente erosivos en el otoño e inicios de primavera. La inclusión de cultivos de trébol y ballico tuvo pequeños efectos positivos en la proporción de suelo cubierto por residuos del cultivo (determinado por el método de línea intercepto) en ambos sistemas de labranza. Se observó un efecto significativo de la labranza sobre el rendimiento total de tubérculos en un ciclo de rotación solamente, cuando el retraso de la labranza hasta la primavera redujo el rendimiento en casi 12%. Los tratamientos con cultivos de cobertura no tuvieron efecto sobre el rendimiento total de tubérculos, tampoco la labranza o cultivos de cobertura afectaron la proporción de tubérculos comerciables. La labranza no afectó la costra negra (Rhizoctonia solani Kühn) ni a la sarna común [Streptomyces scabies (Thaxter) Lambert & Loria], los cuales fueron reducidos significativamente por el trébol rojo en algunos ciclos de rotación. Esta investigación muestra que se pueden implementar las prácticas de conservación, incluyendo el retraso de la labranza principal hasta la primavera, siembra de cultivos de cobertura intercalados durante la fase de formación de grano del cultivo, mientras se mantiene el rendimiento de papa.

Impacts of Crop Rotation and Irrigation on Soilborne Diseases and Soil Microbial Communities

Crop rotation provides numerous benefits to crop production, and is essential to reduce the build-up of soilborne plant pathogens and diseases that can devastate potato crops grown in multiple consecutive years. Crop rotations can reduce soilborne diseases through a variety of mechanisms, including changes in soil microbial communities, but different types of rotation crops can have very different effects. Crop rotations may be implemented as full-season harvestable crops, cover crops, or as green manures, with each approach having different impacts on soilborne diseases. In recent research in Maine, full-season rotation crops, such as barley, ryegrass, canola, and rapeseed, in 2-year and 3-year rotations with potato substantially reduced (15–50% reduction) Rhizoctonia and other soilborne diseases. Addition of a fall cover crop of winter rye to existing rotations further reduced Rhizoctonia and common scab diseases by another 5–20%. Use of specific disease-suppressive rotation crops as green manures can provide even greater reductions in soilborne diseases. In an ongoing large-scale study examining the effects of several different cropping system strategies both with and without irrigation, a disease-suppressive approach (utilizing Brassica and sudangrass green manures, fall cover crops, and high crop diversity) reduced soilborne diseases better than any other cropping system (25–58% reduction), and both the disease-suppressive and a soil improving (with compost amendments) system substantially increased tuber yield (19–42%). Irrigation also increased yield (∼28%) in most systems. Combining the disease-suppressive rotation with irrigation increased yield by 53% relative to non-irrigated continuous potato. Combining effective crop rotations with other compatible components of integrated pest management can provide more effective and sustainable disease management and crop productivity.

Sustainable Potato Production and Global Food Security

The potato (Solanum spp.) is currently the leading non-grain commodity in the global food system with production exceeding 329 million metric tonnes in 2009. The extraordinary adaptive range of this species complex combined with ease of cultivation and high nutritional content have promoted steady increases in potato consumption especially in developing countries. Recent uncertainties in world food supply and demand have placed the potato in the upper echelon of recommended food security crops. This introductory chapter provides the latest updates on geospatial patterns of potato production world-wide. In addition, the potential impacts of climate change, agrobiodiversity, biotechnology, and soil resource management on sustainable potato production are briefly discussed.

Comparison of Soil Phosphorus Status and Organic Matter Composition in Potato Fields with Different Crop Rotation Systems

Cropping management practices influence soil phosphorus (P) availability and soil organic matter (SOM) quality. This chapter summarizes the impact of cropping systems and water management on soil phosphorus status and organic matter characteristics after the first full cycle of the 3-year crop rotations. These data indicated that the 3-year crop rotations impacted more on labile P and organic matter fractions and relevant biochemical parameters (i. e. water extractable P and organic matter, mild modified Morgan soil test P, microbial biomass C and P, phosphatase and urease activities). However, these influences were not always consistent and statistically significant (P = 0.1 or 0.05). Generally, irrigation had a greater influence on stable P and organic matter fractions than crop rotations. Continuous analysis of P and SOM from soils after the completion of the second rotation cycle of the 3-year crop rotations would provide more insights on the improvement of soil fertility and biochemical quality for potato production by crop rotations.

Early and Late Blight Potential on Russet Burbank Potato as Affected by Microclimate, Cropping Systems and Irrigation Management in Northeastern United States

Soil and irrigation management have been used to optimize crop production; however, their effects on microclimate, development, and control of potato diseases have not been adequately quantified. The effects of soil, crop, and water management on development of potato early blight and late blight were quantified in a potato cropping systems experiment from 2006 to 2008. Microclimate, (soil temp, air temp, relative humidity, soil water content and leaf wetness) was not significantly impacted by cropping systems, and varied within seasons and across years. Irrigation management had little impact on microclimate, suggesting that treatment induced effects were not significant. Early blight incidence, severity, and lesion numbers were, however, impacted by management systems and years. Disease incidence was significantly (P 90%, predicted area under disease progress curves (AUDPC), severity values, and blight units had similar values among cropping systems and water management. Microclimatic variables were not significantly correlated to early blight or late blight potential, perhaps due to the small-scale size of experimental plots and influence of the surrounding environment, or lack of significant treatment effects. In addition to the positive attributes often associated with potato cropping systems (increased crop growth, yield, soil health, economic returns, production sustainability), this research demonstrated improved management of potato early blight with cropping systems, but no effect on late blight, a potentially explosive foliar disease. Nevertheless, cropping systems and irrigation management provide useful tools for the enhanced sustainability of potato production systems.