David F. Bezdicek

The need for a soil quality index: Local and regional perspectives

Granatstein, D. and D.F. Bezdicek. 1992. The need for a soil quality index: local and regional perspectives. Amer. J. Alternative Agriculture 7:12-16.

Long-term tillage and rotation effects on soil microbial biomass, carbon and nitrogen

SummaryThree mollisols, typical of the Palouse winter wheat region of eastern Washington and northern Idaho, were analyzed for microbial biomass, total C and total N after 10 years of combined tillage and rotation treatments. Treatments included till, no-till and three different cereal-legume rotations. All crop phases in each rotation were sampled in the same year. Microbial biomass was monitored from April to October, using a respiratory-response method. Microbial biomass, total C and total N were highest under no-till surface soils (0–5 cm), with minimal differences for tillage or depth below 5 cm. Microbial biomass differences among rotations were not large, owing to the relative homogeneity of the treatments. A rotation with two legume crops had the highest total C and N. Microbial biomass was significantly higher in no-till surface soils where the current crop had been preceded by a high-residue crop. The opposite was true for the tilled plots. There was little change in microbial biomass over the seasons until October, when fresh crop residues and rains had a strong stimulatory effect. The seasonal pattern of biomass in no-till surface soils reflected the dry summer/winter rainfall climate of the region. The results of this study show that numerous factors affect soil microbial biomass and that cropping history and seasonal changes must be taken into account when microbial biomass data are compared.

Soil water and nitrogen dynamics in dryland cropping systems of Washington State, USA

Understanding the fate of soil water and nitrogen (N) is essential for improving crop yield and optimizing the management of water and N in dryland cropping systems. The objective of this study was to evaluate how conventional (CT) and no-till (NT) cropping systems affect soil water and N dynamics. Soil water and N were monitored in 30 cm increments to a depth of 1.5 m for 2 years at growers’ fields in two different agroclimatic zones of Washington State (USA): (1) the annual cropping region with a mean annual precipitation of more than 500 mm (Palouse site) and (2) the grain-fallow cropping region with mean precipitation below 350 mm (Touchet site). In each zone, a CT and a NT cropping system were chosen. All sites had an annual cropping system, except for the CT site in the drier area, which was under a traditional winter wheat/fallow rotation previous to the study. At Palouse, the volumetric water content in the top 1.5 m of the soil throughout the year was about 0.05–0.1 m 3 m −3 less under CT as compared to NT, indicating improved seasonal accumulation and distribution of soil water under NT. Cropping systems modeling indicated, that during winter, surface runoff occurred in the CT system, but not under NT. The differences in soil water dynamics between CT and NT were mainly caused by differences in surface residues. Dynamics of NO3 − -N at Palouse were similar for NT and CT. At Touchet, differences in soil moisture between NT and CT were less than 0.05 m 3 m −3 . Under NT, high levels of NO3 − -N, up to 92 kg NO3-N ha −1 , were found after harvest below the root zone between 1.5 and 2.5 m, and were attributed to inefficient use or over-application of fertilizer. In both climatic zones, grain yield was positively correlated with evapotranspiration.

Effectiveness and competitiveness of spontaneous antibiotic-resistant mutants of Rhizobium leguminosarum and Rhizobium japonicum

Abstract Thirteen doubly-marked antibiotic-resistant isolates of Rhizobium leguminosarum and three resistant isolates of R. japonicum were developed and tested for effectiveness of N2-fixation and competitiveness. Ninety-three percent of the mutants isolated were less competitive in nodule-forming ability, than their parents. However, only 38% of the R. leguminosarum isolates were reduced in N2-fixation effectiveness when compared to their parents. Doubling times of the R. leguminosarum mutants increased when compared to their parents. No correlation was found between nodulation competitiveness and doubling time of the mutants. R. leguminosarum mutants in the nodules were evaluated using a new procedure, which facilitates the handling of large numbers of nodules.

End Product Quality and Agronomic Performance of Compost

Washington State University produces a manure-based compost of high pH (>8) and low N content (1 percent) by windrow composting campus wastes. Annual production at the four-acre facility is 18-20,000 cubic yards. In the interest of producing compost of higher N content and lower pH, ten experimental piles were constructed to investigate the effects of different feedstocks on the composting process, end quality and agronomic performance. Biosolids and manure were compared at two rates of bedding both with and without coal ash. Compost temperature and inorganic N content during 96 days of active composting are reported along with end product nutrient analysis and metal concentration. The composts behaved differently based on the N feedstock and level of bedding in the mix. Compost quality was influenced by the characteristics of the feedstocks. Applying the composts to an eroded hilltop (50 Mg/ha) increased winter wheat yield, but there were no differences among the ten composts.

Crop rotation efficiencies and biological diversity in farming systems

The positive role of biological diversity in enhancing agricultural sustainability is presented in the context of crop rotation. Once common in virtually all farming systems, crop rotations have been simplified or eliminated during the past two decades from farming systems in most industrialized countries. Specialization, production intensification, government commodity programs, and the resulting short-term economic decisions have all had an influence in reducing crop rotation and diversity. Economic and environmental concerns have raised the question of agricultural sustainability in the public arena. We discuss here the role of diversity and crop rotation in relation to the sustainability issue, including matters of agronomic, economic, and environmental benefits, as well as increased efficiency in the use of fossil fuels. Constraints and future directions in the use of crop rotation in modern agriculture are described.

Insecticidal activity and competitiveness of rhizobium spp containing the bacillus thuringiensis subsp.tenebrionis δ-endotoxin gene (cryIII) in legume nodules

Abstract Strains of Rhizobium leguminosarum and Rhizobium meliloti were constructed by cloning the cryIII gene (the gene encoding for the insecticidal CryIII protein) from Bacillus thuringiensis subsp. tenebrionis into the broad host-range vector, pRK311, containing a constitutive lacZ promoter that codes for lactose utilization or a conditional nifH promoter that is involved in nitrogen fixation. The cryIII -containing rhizobia (i.e. Cl-pBtt-LZ and Cl-pBtt-nH) expressed toxin in sufficient quantities within root nodules to reduce significantly feeding damage by the nodule-feeding insects, Sitona lineatus on Pisum sativum and Sitona hispidulus on Medicago sativa . The pRK311 plasmid remained stable in the rhizobia that were either free-living or within nodules of the legumes. The engineered cryIII -containing strains of R. leguminosarum were equally competitive with the wild-type parental strain and a kanamycin-resistant strain. The engineered strains occupied 40–97% of P. sativum nodules. However, plant biomass was significantly reduced in plants inoculated with single isolates of the pRK311 -based strains, C1 -pRK311, C1 -pBtt-LZ or Cl-pBtt-nH. The biomass of plants increased significantly when plants had also been inoculated with wild-type strains.

Impairment of transposon-induced mutants of Rhizobium leguminosarum

Abstract Tn 5 mutagenesis was investigated as a technique to genetically mark Rhizobium for soil microcosm studies. Sixteen mutants created by Tn 5 insertion or suicide vector integration were analyzed to determine how the mutations affected several phenotypic traits. These included growth rate in culture, symbiotic effectiveness, and competitiveness for nodule occupancy. Seven of 10 Tn 5 -containing strains and 5 of 6 vector-integrate strains were impaired in one or more phenotypic traits in comparison to their parent. These results illustrate the need to carefully characterize genetically marked organisms instead of assuming the marked organism is simply an antibiotic-resistant strain equal to the parent.

Cloning Bacillus thuringiensis toxin genes for control of nodule-feeding insects

The cry III endotoxin gene from Bacillus thuringiensis subsp. tenebrionis was cloned into strains of Rhizobium leguminosarum and R. meliloti. Strains were constructed that used a constitutive lacZ promoter or a conditional nifH promoter. Cry III toxin expression in nodules resulted in significant reductions in nodule-feeding damage by Sitona lineatus on Pisum sativum and S. hispidulus on Medicago sativa. Results from a greenhouse experiment indicated that the genetically engineered rhizobia were competitive with the parent wildtype strain of R. leguminosarum and with the same strain containing Tn5 in the chromosome. Biomass of P. sativum was reduced when plants were inoculated with single strains of the engineered rhizobia, but were not affected when coinoculated with wildtype rhizobia.