The Environmental Consequences of the Conservation Tillage Adoption Decision in Agriculture in the United States

The environmental consequences of conservation tillage practices are an important issue concerning the impact of agricultural production on the environment. While it is generally recognized that water runoff and soil erosion will decline as no tillage and mulch tillage systems are used more extensively on cropland, what will happen to pesticide and fertilizer use remains uncertain. To gain some insight into this, the conservation tillage adoption decision is modelled. Starting with the assumption that this dicision is a two step procedure – the first is the decision whether or not adopt a conservation tillage production system and the second is the decision on the extent to which conservation tillage should be used – appropriate models of the Cragg and Heckman (dominance) type are estimated. Based on farm-level data on corn production in the United States for 1987, the profile of a farm on which conservation tillage was adopted is that cropland had above average slope and experienced above average rainfall, the farm was a cash grain enterprise, and it had an above average expenditure on pesticides and a below average expenditure on fuel and a below average expenditure on custom pesticide applications. Additionally, for a farm adopting a no tillage production practice, an above average expenditure was made on fertilizer.     

Biomass production, foliar and root characteristics and nutrient accumulation in young silver birch (Betula pendula Roth.) stand growing on abandoned agricultural land

The above-ground biomass and production, below-ground biomass, nutrient (NPK) accumulation, fine roots and foliar characteristics of a 8-year-old silver birch (Betula pendula) natural stand, growing on abandoned agricultural land in Estonia, were investigated. Total above-ground biomass and current annual production after eight growing seasons was 31.2 and 11.9 t DM ha⁻¹, respectively. The production of stems accounted for 62.4% and below-ground biomass accounted for 19.2% of the total biomass of the stand. Carbon sequestration in tree biomass reaches roughly 17.5 t C ha⁻¹ during the first 8 years. The biomass of the fine roots (d < 2 mm) was 1.7 ± 0.2 t DM ha⁻¹ and 76.2% of it was located in the 20 cm topsoil layer. The leaf area index (LAI) of the birch stand was estimated as 3.7 m² m⁻² and specific leaf area (SLA) 15.0 ± 0.1 m² kg⁻¹. The impact of the crown layer on SLA was significant as the leaves are markedly thicker in the upper part of the crown compared with the lower part. The short-root specific area (SRA) in the 30 cm topsoil was 182.9 ± 9.5 m² kg⁻¹, specific root length (SRL), root tissue density (RTD) and the number of short-root tips (>95% ectomycorrhizal) per dry mass unit of short roots were 145.3 ± 8.6 m g⁻¹, 58.6 ± 3.0 kg m⁻³ and 103.7 ± 5.5 tips mg⁻¹, respectively. In August the amount of nitrogen, phosphorus and potassium, accumulated in above ground biomass, was 192.6, 25.0 and 56.6 kg ha⁻¹, respectively. The annual flux of N and P retranslocation from the leaves to the other tree parts was 57.2 and 3.7 kg ha⁻¹ yr⁻¹ (55 and 27%), respectively, of which 29.1 kg ha⁻¹ N and 2.8 kg ha⁻¹ P were accumulated in the above-ground part of the stand.     

A regret function for agricultural production systems

Decision-making under uncertainty is a difficult task, involving risks. Since losses are to be expected although not necessarily through the decision-maker's fault, a regret concept is adopted. A regret concept and a regret function, based on a linear programming model, are suggested, using analysis of the sensitivity of the optimal plan to changes in random prices and in the amounts of available resources and estimates of the probabilities that each of the random variables will drop below a critical value. The use of this regret function, as an aid in decision-making, to evaluate the plan at the planning stage is explained and clarified by examples and a case study.     

Spatial distribution of water status in irrigated olive orchards by thermal imaging

Information regarding tree water status in irrigated olive orchards is essential for managing growth to optimize yields and olive oil quality. One management practice option is to monitor or sample individual trees and use this information for orchard-scale management. This study assessed the ability of thermal imaging to provide the spatial distribution and variability of tree water status in a commercial irrigated olive orchard, and described strategies and a procedure for choosing which individual trees best represent the orchard. The study employed gradual upscaling from individual trees grown in lysimeters, through a controlled experimental field plot, to a commercial orchard. Thermal imaging of olive trees grown in lysimeters attested the sensitivity of the technique to identify mild-level water stress by correlating crown temperatures to stem water potential. Knowledgeable choice of five or ten representative trees in the experimental plot, based on the histogram distribution obtained for the entire experimental orchard, lead to successful reconstruction of the spatial distribution of canopy temperature, and thus of water status. Positively skewed distributions of crown temperatures found in both the field plot and commercial orchard suggested distinct patterns, where the canopy temperature of the majority of the trees was lower than the average, and a relatively small number of trees had significantly higher temperatures and suggest commercial practicality of the proposed methodology. Thermal imaging can therefore serve as a useful tool for determining representative trees that, if frequently monitored, or instrumented with continuous water status sensors, can provide important information for orchard water management.     

Assessment of genetic relatedness in carnation by DNA fingerprint analysis

Summary DNA fingerprinting analysis of genetic relatedness between carnation genotypes using human derived minisatellite probes, correctly reflected relationships within and between categories of carnation plants with inferred relatedness. Similar DNA fingerprint patterns were observed between genotypes within either standard or spray categories. A high level of similarity was also detected between those categories. Moderate similarities were found within the dwarf category, and between dwarf and either standard or spray categories. Large differences were observed between a wild species and cultivated categories. Abbreviations: b.1.-breeding line, BS-band-sharing     

Fluidity of bound hydration layers

We have measured the shear forces between solid surfaces sliding past each other across aqueous salt solutions, at pressures and concentrations typical of naturally occurring systems. In such systems the surface-attached hydration layers keep the compressed surfaces apart as a result of strongly repulsive hydration forces. We find, however, that the bound water molecules retain a shear fluidity characteristic of the bulk liquid, even when compressed down to films 1.0 +/- 0.3 nanometer thick. We attribute this to the ready exchange (as opposed to loss) of water molecules within the hydration layers as they rub past each other under strong compression.     

Analysis and assessment of precipitation chemistry at Caribou,Maine

Over the last 30 yr, Caribou, Maine has been the only U.S. collection site which has been a part of all four national precipitation chemistry networks. Due to its remote but strategically important location, the data from this site are very useful in evaluating transboundary transport of the major ions present in precipitation. This paper assesses the reliability of the Caribou data base and looks at the more recent data with the aid of the GAMBIT (Gridded Atmospheric Multilevel Backward Isobaric Trajectory) model. An examination of the historical data base indicates serious contamination problems in pre-1980 samples, particularly with S0₄ measurements. The trajectory climatology shows that the largest number of precipitation events track along the U.S. coast. Preliminary chemistry measurements indicate highest concentrations of H+ and S0₄ occur from events associated with trajectories passing through southern Canada.