Though mulching with polyethylene film has been commonly used for sweet potato cultivation in Ibaraki prefecture, the film is still removed by hand. Since this is laborious work in a dusty environment, a mulching film remover was developed. First, a series film tension tests was conducted to clarify the maximum applicable tensile force. The results showed that the tear resistances of the films was in the range of 60-155kN, hence the pulling force should be kept below 60N. An experimental self-propelled film remover was constructed and tested in actual fields. During these experiments, films were torn frequently in fields with hard compacted soil, thus we had to test the performance of soil-softening devices. We confirmed that tearing of the film could be prevented by the application of sub soilers, but such sub soilers hindered the operation of farm vehicles.
Based on these results, a tractor mounted film remover was developed. The machine was composed of a main frame, a pair of sub soilers, a film pulling up machine with two rubber rollers rotated by a DC powered motor and a steel rod drum for removing soil from the film. The experimental film remover successfully removed and collected mulching films even in compacted fields, and its field capacities were 1h/10a for film removal and 0.5h/10a for film collection. The field capacities of the film remover were the same as those of manual removal, but operation of the remover requested much less effort that the removal by hand.

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In order to apply the LCA method in evaluating environmental measures in agricultural activities, the first task is to draw up scenarios of alternatives for problem solving and subject them to analysis. Secondly, processes and items related to load calculation of life cycle need to be selected and basic data prepared. Then environmental loads produced throughout the life cycle for each scenario need to be calculated.
In this paper, based on the assumption that the Life Cycle Assessment (LCA) would be used to evaluate measures to reduce environmental loads discharged in the process of agricultural nutrient input, attempts are made to calculate energy consumption and CO₂ emissions throughout the life cycle of chemical fertilizer (nitrogen fertilizer, phosphate fertilizer, compound fertilizer and coating fertilizer) productions and transportations, which will provide basic data.
The life cycle energy (LC-energy) in the manufacturing of urea, ammonium sulfate, diammonium phosphate (DAP), compound fertilizer and coating fertilizer were found to be 22.3MJ per 1kg of fertilizer (48.6MJ/kg-N), 4.3MJ/kg (20.5MJ/kg-N), 13.2MJ/kg (28.6MJ/kg-P), 2.0MJ/kg and 1.9MJ/kg respectively. Life cycle CO₂ (LC-CO₂) were 732g-CO₂ per 1kg of fertilizer (1.59kg-CO₂/kg-N), 262g-CO₂/kg (1.25kg-CO₂/kg-N), 894g-CO₂/kg (1.94kg-CO₂/kg-P), 142g-CO₂/kg and 137g-CO₂/kg respectively. Percentages of CO₂ emitted during the transportation stage were approximately 2% for urea and 17% for DAP. In the production of DAP, about 16% of LC-CO₂ was generated at the material collection stage. LC-energy figures obtained in this analysis are considered reasonable in comparison with existing figures.

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To address the problem of uneven moisture conditions of the rootballs of cabbage plug seedlings grown with conventional mist irrigation, we trialed the use of ebb and flow irrigation. We also attempted to improve the quality of the seedlings by adding NaCl to the culture solution. We obtained the following results.
1. With the ebb and flow irrigation system, 20% less working time was required than with conventional mist irrigation.
2. Ebb and flow irrigation promoted growth uniformity of seedlings and improved growth after transplanting.
3. Adding NaCl at a density of 0.3% to the culture solution encouraged greening of leaves and a decrease in the flat rate of plant appearance.
4. When NaCl was added early, seedling growth was greatly depressed.
5. Addition of NaCl 5 days before transplanting did not decrease yield.
6. Plug seedlings exposed to added NaCl acquired drought tolerance, as shown by both improvement of water-use efficiency and the results of electrolyte leakage testing after drought treatment.
7. Yield was higher with ebb and flow irrigation than with conventional mist irrigation.
Use of an ebb and flow irrigation system reduced labor costs, improved the uniformity of seedlings, and enhanced seedling growth after transplanting. Furthermore, adding NaCl at 0.3% 5 days before transplanting improved the adaptability of seedlings to the automatic transplanter and improved their drought tolerance with-out decreasing cabbage yield.

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Diggers of the backhoe type, the trencher type, and the plow type have been mainly used to harvest Chinese yams until now. Recently, diggers that can continuously dig the tubers have been developed and the farmers are using them. The harvest system, working capacity, operating accuracies, cost and the coverage of the three diggers (A, S, T) that had been developed in recent years were compared with the conventional type (K).
1) Much labor is necessary, when the working capacity of digger is generally high.
2) The working capacities for diggers A, K, S, T are respectively 0.58, 0.22, 0.38, 0.37ha/h and the worker-hour per hectare is 208 for A, 210 for S, 219 for T, and 278-323 worker-hours per hectare for K.
3) There were no tubers damaged by a mechanical cause in any digger though there were tubers damaged by the labor. The ratio of undamaged tubers was more than 98% for each digger.
4) Coverage that can be harvested for yams during the harvest season is 4ha for A, 1.5ha for K, and 2.5ha for S and T. The costs per hectare are 556, 000, 1, 113, 000-1, 173, 000, 687, 000, and 699, 000 yen respectively. The profitable minimum working areas are the range of 0.49-0.56ha for each machine.
Digger A is suitable for use by a large scale farmer and K is suitable for use by a small scale farmer because it can be used by a few people. In addition, S and T are suitable for use by a middle scale farmer.

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