Japanese Journal of Soil Science and Plant Nutrition

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In a drip-application (fertigation) culture, plant nutrients are supplied both from nutrient solution and from soil media. The objective of this study was to determine whether the nutrients such as phosphorus or bases should be added in the solution or to the soil. Melon and tomato plants were successively cultivated with drip-application of nitrogen solution or mixed nutrient (N, P, K, Mg, Ca) solution. Before each transplanting, the soil was tested for phosphorus and bases, and supplemented with liming materials, potassium, and phosphorus aiming at 80% of base saturation and 300 mg kg^<-1> of Truog-P_2O_5. Those targets are the standard level of soil chemical improvement, but less than recent soil amounts for greenhouse culture in Japan. 1) Melon and tomato growth was affected strongly by application of nutrient solution. Regardless of soil chemical improvement, their harvest and the absorption of P and K were higher in the mixed nutrition treatment than in the nitrogen treatment. When nitrogen solution was applied in the chemically improved plots, plant harvests were as high as in the control plot (conventional soil culture). However, the absorption of nutrients, particularly of potassium, decreased markedly in the later stage of cultivation. When nitrogen solution was applied in the non-improved plots, plant harvests and sugar contents were too low. 2) The roots of plants were concentrated in the soil near emitters of drip tubes, and were few between plant hills. Contents of bases in the soil after cultivation were decreased in the vicinities of the emitters but not much changed between plants. These findings suggest that in drip-application culture, the nutrients like P and K which are not very mobile in soil media, should be applied in the solution, rather than applied uniformly in the soil media. 3) In this experiment the addition of magnesium and calcium to the solution was not so effective. The plant growth depended so strongly on potassium application, that magnesium and calcium may have affected antagonistically the absorption of potassium, when they were added to the solution. 4) Soil chemical improvement affected plant growth and yield. Therefore, it is considered that soil analysis and diagnosis are important even in a drip-application culture.

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^<15>N-labeled composted manure was produced using five adult dairy cows and 420 m^2 of grassland and the flow of ^<15>N during the process was analyzed. Cows were fed ^<15>N-labeled Dactylis gromerata 1st cut silage containing 6.2 atom% ^<15>N. After 2 days, ^<15>N concentration in their feces increased significantly, reaching 4.95 atom% ^<15>N at the 10th day, and ^<15>N concentration was almost stable after 8 days. Cows were subsequently fed 2nd cut silage containing 4.0 atom% ^<15>N, resulting in a slight decrease in ^<15>N concentration. However, ^<15>N concentration remained high at approx. 3 atom% ^<15>N, and decreased immediately after non ^<15>N-labeled hay was fed upon completion of the 17-day procedure. Results of ^<15>N concentration in urine were almost parallel with those for feces, although ^<15>N concentration was significantly lower. In order to increase ^<15>N concentration, feces and urine excreted when ^<15>N concentration in the feces exceeded 3 atom% ^<15>N were used for production of the compost. After dehydrating the feces to 68 kg kg^<-1> water content and concentrating the urine in a heating oven at 80℃, the dried feces and concentrated urine were mixed and composted in an air sucking composter for 4 weeks. One hundred and forty seven kilograms of composted manure was obtained, containing 3.95 atom% ^<15>N and 50 kg kg^<-1> water. Uniformity of labeled ^<15>N was determined by fraction separation through acid hydrolysis differing by acid concentration, and almost uniform homogeneity was confirmed. Satisfactory compost manure labeled ^<15>N was obtained using this procedure. Relative N recovery ratio compared to the amount of N contained in the applied ^<15>N labeled fertilizer was 23.6% in excreta, with the loss of 11.1% during drying and composting, and 10.6% N remained in the final composted manure.

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We reported previously that the accumulated amount of absorbed nitrogen increased linearly during the fruit growing stage in the Japanese pear (Pyrus pyrifolia Nakai) 'Kousui.' In the present study, the influence of nitrogen top dressing at the fruit growing stage was investigated in 'Kousui' to develop an efficient method for nitrogen application. With application of 15% of the total amount of nitrogen at both the early (early May) and middle stages (early June) of fruit growing, the fruit weight was increased significantly as compared with cultivation without top dressing. Even with a reduction in amount of nitrogen to 20%, the fruit with the top dressing grew as large as that given the standard amount for Ibaraki Prefecture. In plots with the top dressing, the NO_3-N concentration in the soil solution at the rhizosphere (depth, 20cm) was higher than that without top dressing during the fruit growing stage. These results indicated that the method of nitrogen top dressing conforms to the nitrogen accumulation characteristics of 'Kousui' reported previously, and it is possible to reduce the nitrogen level by 20% as compared to the standard amount using this method. The NO_3-N concentration in the groundwater of the experimental field where the standard amount of nitrogen had been applied ranged from 4.9 to 9.5mg L^<-1>, which was below the environmental standard of 10mg L^<-1>.

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In order to determine the optimum water supply for dry matter production of orchardgrass (Dactylis glomerata L.) in the second and the third growing period respectively, the effect of water supply in orchardgrass on growth was studied by analyzing the relation between the nitrogen uptake by grass and the yield components. The results were as follows. 1) For the second growing period of orchardgrass, the lack of water supply in the early stage, which was a period of about 20 d after the time of the first cutting, resulted in a remarkable decrease in the yield of grass. 2) For the third growing period, the yield of orchardgrass obviously decreased when water was not supplied in the early stage which was about 10 d after the time of the second cutting. 3) These findings were ascribed to the fact that the weight per tiller, which strongly affected the yields of both the second and the third cutting, could not increase sufficiently throughout the experimental periods, because the lack of water supply restricted nitrogen absorption by orchardgrass and then delayed the regrowth of tillers. 4) The results obtained in the present study showed that the optimum water supply for dry matter production of orchardgrass during the second and the third growing period was as follows respectively: a) the second growing period: the early stage (about 20 d after the time of the first cutting), b) the third growing period: the early stage (about 10 d after the time of the second cutting).

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