Robert I. Papendick

Considerations in estimating Nitrogen Recovery Efficiency by the difference and isotopic dilution methods

Nitrogen Recovery Efficiencies (NRE) as calculated by the Isotopic dilution technique or the difference method are subject to errors under different conditions. The assumptions underlying these methods and the conditions and factors that must be considered while using these methods have been discussed. Majority of the reports suggest that the difference method gives higher values than the isotopic dilution technique. Results of a pot experiment show the importance of accounting the N held in roots for estimating NRE by either of the methods. Although the isotopic dilution technique has been invariably more precise, it was not necessarily representing the true NRE value. Contrary to some earlier reports, it was observed that Added Nitrogen Interaction (ANI) occurred even in field experiments. Guidelines are provided to assist researchers in assessing the validity of using isotopic or difference method in a given situation. For conditions where the NRE values obtained by either of the methods are influenced by ANI, a method of correcting the NRE values has been suggested, to arrive at the most probable value.

Integration of multiple soil parameters to evaluate soil quality: a field example

Development of a method to assess and monitor soil quality is critical to soil resource management and policy formation. To be useful, a method for assessing soil quality must be able to integrate many different kinds of data, allow evaluation of soil quality based on alternative uses or definitions and estimate soil quality for unsampled locations. In the present study we used one such method, based on non-parametric geostatistics. We evaluated soil quality from the integration of six soil variables measured at 220 locations in an agricultural field in southeastern Washington State. We converted the continous data values for each soil variable at each location to a binary variable indicator transform based on thresholds. We then combined indicator transformed data for individual soil variables into a single integrative indicator of soil quality termed a multiple variable indicator transform (MVIT). We observed that soil chemical variables, pools of soil resources, populations of microorgansims, and soil enzymes covaried spatially across the landscape. These ensembles of soil variables were not randomly distributed, but rather were systematically patterned. Soil quality maps calculated by kriging showed that the joint probabilities of meeting specific MVIT selection were influenced by the critical threshold values used to transform each individual soil quality variable and the MVIT selection criteria. If MVIT criteria adequately reflect soil quality then the kriging can produce maps of the probabilty of a soil being of good or poor quality.

Macropore transport of bromide as influenced by soil structure differences

Macropore transport of chemicals in soil often causes unexpected contamination of groundwater. The effect of soil structure on the functions of various sized macropores was assessed, investigating transport of nonreactive bromide (Br) under matric heads of 0, � 2, � 5 and � 10 cm using undisturbed soil columns from A, Bw and E horizons of a Thatuna silt loam soil (fine-silty, mixed, mesic Xeric Argialbolls). The experimental breakthrough curves (BTC) for Br were described with a two-region physical nonequilibrium model. Greatest macroporosity occurred in the A horizon and lowest in the E horizon. The measured pore water velocity m under saturated conditions ranged from 18.92 cm day � 1 in the E horizon to 64.28 cm day � 1 in the A horizon. While the greatest dispersivity k occurred in the Bw horizon due to medium subangular blocky and prizmatic aggregates, the lowest dispersivity occurred in the E horizon due to its low macroporosity and massive structure. The fitted mobile water partitioning coefficient b ranged from 0.30 in the A horizon under 0 cm matric head to 0.93 in the E horizon under 0 cm matric head. The calculated values of rate of diffusive mass exchange a decreased with decreasing matric head in A and Bw horizons, and slightly increased and then decreased in the E horizon. The difference among each of the values of the parameters m, b, a and k for the A, Bw and E horizons was greatest under saturated conditions. However, gradually decreasing matric head until about � 3 cm decreased the difference among the values for a particular parameter for different horizons, sharply. The difference remained fairly unchanged with further decreases in the matric head, suggesting that most of the variability in macropore transport of bromide for these horizons caused by pores with radii larger than about 0.5 mm. In A and Bw horizons, there was a sudden change in soil solution movement between � 2 and � 5 cm matric head, indicating that macropore flow generally occurred at matric heads greater than

Integration of Weed Management and Tillage Practices in Spring Dry Pea Production

Abstract Spring barley can be used to diversify and intensify winter wheat-based production systems in the U.S. Pacific Northwest. The objective of this study was to describe the effects of tillage system and weed management level (WML) on weed control and spring barley grain yield when grown in a winter wheat-spring barley-spring dry pea rotation. A long-term integrated pest management field study examined the effects of three WMLs (minimum, moderate, and maximum) and two tillage systems (conservation and conventional) on weed control and barley grain yield. Total weed biomass at harvest was 8.0 and 59.7 g m−2 for the maximum and minimum WMLs, respectively, in the conservation tillage system, but was similar and averaged 12.2 g m−2 for all three WMLs in the conventional tillage system. Despite greater weed biomass with minimum weed management in the conservation tillage system, barley grain yields averaged 5,060 and 4,780 kg ha−1 for the conservation tillage and conventional tillage systems, respectively. The benefits of conservation tillage require adequate herbicide inputs. Nomenclature: Barley, Hordeum vulgare L.; dry pea, Pisum sativum L.; winter wheat, Triticum aestivum L. Resumen La cebada de primavera puede ser usada para diversificar e intensificar los sistemas de producción basados en trigo en el Pacífico Noroeste de los Estados Unidos. El objetivo de este estudio fue describir los efectos de los sistemas de labranza y el nivel de manejo de malezas (WML) sobre el control de malezas y el rendimiento de grano de cebada de primavera cuando se produjo en una rotación de trigo de invierno-cebada de primavera-guisante de primavera. Un experimento de campo de manejo integrado de plagas de largo plazo examinó los efectos de tres WMLs (mínimo, moderado, y máximo) en dos sistemas de labranza (conservación y convencional) sobre el control de malezas y el rendimiento de grano de la cebada. La biomasa total de malezas al momento de la cosecha fue 8.0 y 59.7 g m−2 para el WMLS máximo y mínimo, respectivamente, en el sistema de labranza de conservación, pero fue similar y promedió 12.2 g m−2 para todos los tres WMLs, en el sistema de labranza convencional. A pesar de que hubo una mayor biomasa de malezas con el manejo mínimo de malezas en el sistema de labranza de conservación, los rendimientos de grano de la cebada promediaron 5,060 y 4,780 kg ha−1 para los sistemas de labranza de conservación y convencional, respectivamente. Los beneficios de la labranza de conservación requieren insumos adecuados de herbicidas.