Richard T. Koenig

Alternative Strategies for Transitioning to Organic Production in Direct-Seeded Grain Systems in Eastern Washington I: Crop Agronomy

Organic grain production is not common to eastern Washington, but offers attractive market opportunities if systems can be developed that are compatible with regional production constraints. Erodible soils make tillage-intensive systems unsustainable, and there are limited alternative fertility options. Given these constraints, the objective of this study was to evaluate nine cropping systems during the transition to organic grain production under reduced tillage and relying on legumes as the primary source of crop nitrogen. The experimental transition systems ranged in the degree in which legume grain crops or legume green manures/forages were present in the rotation. We found that spring pea grown for grain to be a poor choice for organic production due to the susceptibility of this crop to insect pests and weeds, which generally resulted in crop failure. Likewise, bell bean was poorly suited as a legume green manure crop due to its low productivity in our region. In contrast, alfalfa and winter pea-based systems achieved the best legume biomass production, weed suppression, and crop yields in the subsequent crops. Winter wheat substantially out-yielded spring wheat, but the yields of both of these crops were well below the yield potential typically achieved under conventional production. Competition from annual weeds, such as wild oat and prickly lettuce, and the perennial weed field bindweed was difficult to manage under the reduced tillage regimes employed in this study.

Dryland Winter Wheat Yield, Grain Protein, and Soil Nitrogen Responses to Fertilizer and Biosolids Applications

Applications of biosolids were compared to inorganic nitrogen (N) fertilizer for two years at three locations in eastern Washington State, USA, with diverse rainfall and soft white, hard red, and hard white winter wheat (Triticum aestivum L.) cultivars. High rates of inorganic N tended to reduce yields, while grain protein responses to N rate were positive and linear for all wheat market classes. Biosolids produced 0 to 1400 kg ha−1 (0 to 47%) higher grain yields than inorganic N. Wheat may have responded positively to nutrients other than N in the biosolids or to a metered N supply that limited vegetative growth and the potential for moisture stress-induced reductions in grain yield in these dryland production systems. Grain protein content with biosolids was either equal to or below grain protein with inorganic N, likely due to dilution of grain N from the higher yields achieved with biosolids. Results indicate the potential to improve dryland winter wheat yields with biosolids compared to inorganic N alone, but perhaps not to increase grain protein concentration of hard wheat when biosolids are applied immediately before planting.

A Comparison of Liquid Phosphoric Acid and Dry Phosphorus Fertilizer Sources for Irrigated Alfalfa Production on Calcareous Soils

Abstract Alfalfa production in the Western United States requires large quantities of phosphorus (P) fertilizer. In 1998, phosphoric acid (PA) became available as a fertilizer source. Phosphoric acid was more expensive per kg of P than other fertilizers, but was promoted on the basis of convenience of application when tank mixed with other chemicals, and superior agronomic performance (higher yield per kg P applied) in alkaline soils due to the neutralizing effect of the acid. The objective of this study was to compare the effects of PA, triple superphosphate (TSP, 0-45-0), and monoammonium phosphate (MAP, 11-52-0) on alfalfa yield and soil and plant tissue nutrient levels. Phosphorus was broadcast at rates based on soil test recommendations for two years at two sites having calcareous soils typical of alfalfa production systems in the Western U.S. At one site, potassium chloride (KCl, 0-0-60) and zinc sulfate were also mixed with the PA based on soil test recommendations. Responses to fertilizer ranged from less than 1 Mg/ha (7 to 10%) to above 6 Mg/ha (44 to 62%) relative to the control. Yield and soil test P were not significantly different among fertilizer sources in either year or location. At one location where more intensive soil and plant tissue testing was done, there were no differences among fertilizer sources in soil or tissue test K or micronutrient concentrations. These results indicate that PA does not have an agronomic (yield) benefit relative to traditional dry P fertilizers for alfalfa produced on calcareous soils. Therefore, the higher cost per kg of P with PA would have to be justified by considerations other than agronomic performance.

Effect of Seed-Row Placement of Conventional and Polymer-Coated Urea on Winter Wheat Emergence

Polymer-coated urea (PCU) may facilitate nitrogen (N) placement with the seed. Laboratory experiments evaluated the effect of (i) variety and N treatment and (ii) urea contact with the seed on winter wheat (Triticum aestivum L.) emergence. Four varieties were grown in a silt loam soil (–200 kPa Ψm, where Ψm is matric potential) with control (0 kg N ha−1), PCU treatment (44% N) at 56, 112, and 168 kg N ha−1, or urea treatment (56 kg N ha−1) placed with the seed. One variety had less emergence than the control with PCU at N rates ≥112 kg ha−1. Urea delayed and decreased emergence of all varieties. In another experiment, urea (56 kg N ha−1) was placed in contact with or between seeds. The contact treatment exhibited delayed and lower emergence. The no-contact treatment behaved similar to controls. Large amounts of 44% N PCU can be placed with the seed without reducing wheat emergence when soil Ψm is at least –200 kPa.

Alternative Strategies for Transitioning to Organic Production in Direct-Seeded Grain Systems in Eastern Washington II: Nitrogen Fertility

The nitrogen (N) dynamics of nine rotation systems designed to transition dryland cereal to organic production in eastern Washington State were examined. Systems combined cereal and legumes for grain, forage (FOR), and green manure (GRM). Few differences in N balances and soil inorganic N levels were found among transition systems when poor spring crop establishment resulted in competition from weeds. However, FOR and winter GRM crops produced adequate stands that were competitive with weeds and increased residual soil inorganic N in the final year of the transition. Winter legumes and continuous FOR systems demonstrated the greatest potential to provide a sustainable inorganic N source to subsequent organic cereal crops.

Potential for ammonia volatilization from urea in dryland Kentucky bluegrass seed production systems.

Urea replaced ammonium nitrate (AN) as a nitrogen (N) source for dryland Kentucky bluegrass seed production in the inland Pacific Northwest in the United States. This study assessed ammonia (NH3) volatilization, N recovery, and seed yield from urea as compared to AN. Laboratory incubations indicate NH3 volatilization is greater from soil covered by fresh residue than soil alone or covered by burned residue. Although pH of the fresh and burned residues exceeded 8.0, urease activity in burned residue was <15% of that in unburned residue or soil. Ammonia volatilization from dry urea and fluid urea AN was greater than AN at burned and unburned sites after a 5 October application. Ammonia volatilization was higher and N recovery and seed yield were lower for urea after a 15 November application at an unburned site. To reduce NH3 volatilization, apply urea to fields with low urease activity or moisture content and/or immediately before a significant rain event.

Transition cropping system impacts on organic wheat yield and quality

Organic wheat and small grains are produced on relatively few acres in the inland Pacific Northwest. The objective of this study was to examine how the nitrogen (N) dynamics of cropping systems (CSs) produced during the transition phase impacted organic wheat yield and protein levels in the first 2 years of certified organic production. Certified organic spring wheat (SW) was produced in 2006 and winter wheat (WW) in 2007 following nine, 3-year transitional cereal, small grain and legume-intensive CSs. SW and WW following perennial alfalfa + oat/pea forage or 3 years of legume green manure tended to be more productive than wheat that followed systems that contained a small grain crop for at least 1 year during the transition. In addition to increasing soil N, well-established stands of forage and green manure provided adequate cover to reduce weed establishment prior to organic production. Effective weed control strategies were as important as increasing soil inorganic N levels for improving organic wheat production. Choice of crop type, cultivar and rotation is important in organic wheat systems and in this study, WW had better stand establishment, competition with weeds and higher overall yield than SW and would be a better-suited class of wheat for organic production in situations where spring weeds are the dominant problem. Regardless of CS or crop type, supplemental soil fertility (primarily N) during the organic production phase will be necessary to maintain high soil N levels and wheat yields in these dryland systems.

Influence of Plant Part on Nitrate Concentration in Lettuce and Spinach

ABSTRACT The concentration of nitrate-nitrogen (NO3-N) varies between lettuce (Lactuca sativa L.) and spinach (Spinacia oleracea L.). Nitrate is potentially harmful if consumed in large amounts by humans; therefore, understanding which cultivars and plant parts concentrate NO3-N can be useful in developing approaches to reduce dietary NO3-N intake. We determined NO3-N concentration and distribution in cultivars of field-grown lettuce and spinach. In 2006, NO3-N concentration was highest in the outer leaf whorl and lowest in the center of spinach; no difference was found in lettuce. In 2007, overall soil and tissue NO3-N concentrations were lower and there was no interaction between plant part and species or cultivar and no difference among leaf whorls; all cultivars had higher NO3-N concentrations in the midrib and petiole than in the leaf. Differences in NO3-N concentration and distribution suggest that practices such as cultivar selection and selective removal of high NO3-N parts can lower NO3-N consumption by humans.

Water and Temperature Stresses Impact Canola (Brassica napus L.) Fatty Acid, Protein, and Yield over Nitrogen and Sulfur

Interactive effects of weather and soil nutrient status often control crop productivity. An experiment was conducted to determine effects of nitrogen (N) and sulfur (S) fertilizer rate, soil water, and atmospheric temperature on canola (Brassica napus L.) fatty acid (FA), total oil, protein, and grain yield. Nitrogen and sulfur were assessed in a 4-yr study with two locations, five N rates (0, 45, 90, 135, and 180 kg ha-1), and two S rates (0 and 17 kg ha-1). Water and temperature were assessed using variability across 12 site-years of dryland canola production. Effects of N and S were inconsistent. Unsaturated FA, oleic acid, grain oil, protein, and theoretical maximum grain yield were highly related to water and temperature variability across the site-years. A nonlinear model identified water and temperature conditions that enabled production of maximum unsaturated FA content, oleic acid content, total oil, protein, and theoretical maximum grain yield. Water and temperature variability played a larger role than soil nutrient status on canola grain constituents and yield.

A comparison of base media used for the incubation of plant residues in laboratory experiments

Abstract Laboratory incubation experiments designed to measure potential rates of decomposition and N mineralization from plant residues typically use either sand or soil as a base medium for incorporation of the materials. Few studies have addressed the effects of base media on decomposition and N mineralization, or the interaction between media and incubated materials. This experiment compared the decomposition and net N mineralization rates of four plant residues incubated in the laboratory in both sand and soil base media. Initially, CO2‐C evolution was greater from residues incubated in die soil, while net N mineralization was greater with the residues in sand. After 11 weeks, cumulative net N and C mineralized from residues incubated in either medium were more similar, but differences between media were still present. The form of N recovered differed between the media, with nitrification absent or occurring at a low rate in the sand. Differences in the rate and extent of decomposition and net N mine...