Soilborne Pathogens of Cereals in an Irrigated Cropping System: Effects of Tillage, Residue Management, and Crop Rotation

Irrigated crops are produced on 645,000 ha in east-central Washington and northcentral Oregon (1). Approximately 70% of this cropland is irrigated with water diverted from rivers, while water for the remaining hectares is pumped from deep wells. Much of the irrigated cropland is found in areas of less than 200 mm annual precipitation, where dryland farming is difficult or impossible. Wind erosion is the biggest environmental concern throughout the region (21,31). Major irrigated field crops include potatoes (Solanum tuberosum L.), corn (Zea mays L.), wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), oat (Avena sativa L.), alfalfa (Medicago sativa L.), and dry bean (Phaseolus vulgaris L.). Winter canola (Brassica napus L.) is not yet widely grown but has received increased attention in recent years due to its reported benefits for subsequent crops in the rotation (10). Due to many available crop options, there are no “set” cropping systems. Farmers rotate crops to reduce pests and diseases, optimize water use, and take advantage of current market opportunities. Many deep-well irrigators plant winter wheat on the same field every year. Irrigated wheat grain yields range from 6,000 to 9,400 kg/ha with residue production of 11,000 kg/ha or more. After grain harvest in August, the traditional practice is to burn the stubble and invert the surface soil with moldboard plow tillage in preparation for planting in September. Generally, farmers feel they need to burn their fields because high residue levels hamper planting and to control the problematic grass weed, downy brome (Bromus tectorum L.). Alternatives to field burning are needed to reduce smoke emissions and maintain air quality. Therefore, new crop rotation and stubble management strategies are needed to make no-till (without burning) work. A group of deep-well irrigated wheat farmers approached Washington State University (WSU) and USDA-ARS scientists in 1998 concerning the future of their farming operations. The farmers were concerned about potential regulations to reduce or eliminate cereal stubble burning and desired research on how to farm profitably without field burning. Reduction or elimination of tillage could also reduce soil erosion. The experiment reported here was designed jointly by farmer advisors and WSU and USDA-ARS scientists. The experiment involved both crop rotation and stubble management factors. The objective of the experiment was to determine the feasibility of planting directly into high levels of residue (no-till) as a substitute for burning in irrigated cropping systems. Specific objectives of the larger project were to: 1. Test a 3-year crop rotation of winter wheat–spring barley–winter canola directly planted (no-till) (i) into standing stubble, (ii) after mechanical removal of stubble, and (iii) after burning the stubble. This was compared with the check treatment of annual winter wheat planted after stubble burning + moldboard plowing. 2. Evaluate and develop effective techniques for planting crops into heavy surface stubble using no-till methods. 3. Document cumulative effects of a diverse no-till crop rotation under three stubble management practices on diseases, soil physical and biological properties, water use efficiency, weed ecology, and farm economics, and to compare these effects to those under the check treatment. The experiments reported here were part of objectives 1 and 3, and were designed to answer several root disease questions: (i) Will root diseases increase when tillage is eliminated? Previous work has shown that Rhizoctonia root rot and bare patch can increase in no-till rotations (17,24,27). (ii) Will residue management reduce disease severity? Gaeumannomyces graminis var. tritici (causal agent of take-all) and Fusarium pseudograminearum and F. culmorum (causal agents of Fusarium crown rot) survive in crown tissue, and several studies have shown increases in diseases in no-till systems where residue is left on the surface (2,32). In addition, irrigated winter wheat produces more residue compared to dryland winter wheat, as 1.3 to 2.0 kg of straw is produced for every 1.0 kg grain (9). (iii) Will crop rotation reduce root diseases? Take-all can be controlled by rotating with broadleaf crops such as canola or pea (Pisum sativum L.), which are resistant to take-all (12), but Rhizoctonia solani AG-8 (cause of Rhizoctonia root rot and bare patch) has a broad host range, and ABSTRACT Paulitz, T. C., Schroeder, K. L., and Schillinger, W. F. 2010. Soilborne pathogens of cereals in an irrigated cropping system: Effects of tillage, residue management, and crop rotation. Plant Dis. 94:61-68.