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Real-time control is becoming an integral part of modern machine systems for high-quality agricultural production. Maintaining consistently high-quality agricultural production while keeping up with growing labor shortages is a challenge. Providing a workplace for labourers which meets increasingly rigorous safety requirements and environmental constraints is likewise a challenge. More appropriate energy management and soil management have also motivated real-time control applications. Appropriate sensing and control systems can reduce labor requirements, function in difficult environments, and allow vehicles to adapt to varying soil chemical and physical states. Labor shortages and environmental constraints coupled with the reality of spatial variability of chemical and physical properties among and within agricultural production areas readily explain the migration toward real-time control of agricultural equipment. This paper presents a review of the most recent advances in the development of sensors and controllers for agricultural applications.

An EMI 5005 medical X-ray computed tomography (CT) scanner was used to observe a variety of soils containing seedlings, insects, roots and radio-opaque labeled granules. Techniques were developed for collecting samples from the field and in the laboratory. Appropriate fixtures were developed for supporting the laboratory and field samples in the scanner gantry. Techniques were adopted for quantifying soil moisture and density as well as biological activity. X-ray CT appears to be a useful tool for studying some soil ecological problems.

Animal trampling can affect soil productivity. Several selected soil physical properties and plant growth indicators thought to be affected by animal trampling were measured in three experiments ranging over 8 years. Crops studied included alfalfa (Medicago sativa), Bermudagrass (Cynodon dactylon), and soybeans (Glycine max) following wheat (Triticum aestivum) or rye (Secale cereale). Stocking rates for the experiments ranged from 5 to 18 animals ha−1. Cone penetrometer measurements were consistently higher in grazed areas than in areas protected from grazing. Other physical parameters (infiltration rate, bulk density, water release curve) measurements were sometimes significantly influenced by trampling. Natural densification explained increased bulk densities within protected areas. Trampling altered surface soil structure; however, productivity (root biomass, forage growth) was not significantly reduced.

Real-time control is becoming an integral part of modern machine systems for high quality agricultural production. Maintaining consistently high quality agricultural production while keeping up with growing labor shortages is a challenge. Providing a work place for laborers which meets increasingly rigorous safety requirements and environmental constraints is likewise a challenge, more appropriate energy management and soil management have also motivated real-time control applications. Appropriate sensing and control systems can reduce labor requirements, function in difficult environments and allow vehicles to adapt to varying soil chemical and physical states. Labor shortages and environmental constraints coupled with the reality of spatial variability of chemical and physical properties among and within agricultural production areas readily explain the migration toward real-time control of agricultural equipment. This paper presents a review of the most recent advances in the development of sensors and controllers for agricultural applications.

X-ray computed tomography is a useful tool for investigating soil physical properties nondestructively. There is a need to develop proper calibration relationships between soil properties and the x-ray absorption coefficient. The objective of the work was to evaluate soil factors affecting the x-ray absorption coefficient. Based on a theoretical analysis, experimental data from five soils and on results of several other investigators, it was concluded that for many applications, one calibration relationship is applicable to a wide range of soils. The montmorillinitic clay used in the study required special handling due to the extreme shrinkage of this soil upon drying. Knowledge of chemical composition enables approximations but not exact predictions of the x-ray absorption coefficient. The results suggested some reasonable alternative to exhaustive calibration for each anticipated soil condition. Quantification of root activity in terms of root growth and indirectly through water uptake is necessary for understanding plant growth dynamics. X-ray computed tomography (CT) enables qualitative as well as two quantitative outputs, one of which can lead to conclusions regarding root activity. A greenhouse study involving soil columns (Lakeland sand, bulk density 1.4 Mg/m{sup 3}) planted to soybean, Bahiagras, and control (no vegetation) was conducted in 1989. A treflan based more » on chemical barrier was placed in half of the soil column of each species. The mean x-ray absorption correlated to water content. Results suggested that root presence can also be indirectly inferred based on water content drawn down during planned stress events. It was concluded that x-ray CT may have a niche in soil-water-plant relation studies, particularly when plant species have large roots. 35 refs., 13 figs., 8 tabs. « less

Procedures have been adapted for characterizing agricultural wastes and residues in terms of carbohydrate content. Carbohydrates, as used in this paper, refer to that fraction of hexan, xylan and uronide sugar classes which are made soluble in a mild acid treatment. Such carbohydrate characterization facilitates the observation of utilization/synthesis patterns within the sugar classes as a waste or residue undergoes decomposition. The hydrolysis and analysis procedures presented can be easily implemented in waste/residue research laboratories and their use could provide interesting insights into other waste and residue-based processes.

In an effort to evaluate an approach to lagoon sealing using organic residues, two crop residues, cotton gin trash and ground corn cobs, and a control soil were subjected to percolating deionised water (low head) for intervals up to 40 days. Water percolation rates through the gin trash, corn cobs and control soil were measured throughout the interval. Percolant microbial numbers (aerobes, anaerobes and numbers on coliform media) were enumerated. Results relating to percolant Total Solids and percolant Volatile Solids were also obtained, along with percolant pH. Carbohydrates present in the solids were characterised throughout the interval, as were solids nitrogen and solids settlement/swelling. These results were helpful in understanding what physical and biochemical effects one could expect in applications such as lagoon sealing where residues are subjected to a low, constant hydraulic head as decomposition progresses.

The microbial kinetics of methane fermentation in anaerobic digestion of organic wastes have been traditionally described using studies of pure substrates, relatively isolated cultures and continuous flow biological reactors. A study involving semi-batch continuously loaded anaerobic digesters using swine waste has demonstrated that the conventional mathematical description of microbial growth kinetics under inhibiting conditions is not sufficient. One inherent problem encountered in mathematical modelling of biological waste treatment processes is sufficient description of the complex organic substrate. Regardless of the composition of this substrate, or the operational mode of the reactor (batch, semi-batch or continuous flow), the microbial kinetics of any system that has the same groups of organisms present must be the same. The difference in these systems is that they are described by different mass balances, not by different microbial kinetics. Conventional kinetics has proved to be totally inaccurate in describing the operation of these semi-batch reactors under inhibited conditions and has led to the development of a new kinetic description that accurately describes both semi-batch and continuous flow reactors in the inhibited and non-inhibited states.