芝生管理方法と芝草の養分吸収の関係について : バミューダーグラスとケンタッキーブルーグラス混植芝生

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To investigate the seasonal uptake of nutrients by turf grass on an area basis is important for two reasons: (1) to maintain good turf condition with appropriate fertilizer management; and (2) to prevent environmental pollution with excess nitrate and acidification of soils by excess application of fertilizers. There have been few studies about this topic because of difficulties in measuring the uptake rate of nutrients by turf grass per area, which fluctuate with species of grass, and a growing number of confounding management practices such as cutting interval and the amount and interval of fertilizer application, and the affects of seasonality. We investigated the uptake of three major nutrients (N, P_2O_5, K_2O) by turf grass (mixed planting of Bermuda grass with Kentucky bluegrass) at one week intervals during May to end of September, which corresponds to the growing season in relation to the management of a turf ground in Ikuta Campus, Meiji university. The results are as follows. 1. Rates of yield of fresh matter and dry matter. The monthly average yield of fresh matter was about 140g/m^2 during May to end of September, but the growing rate fluctuated seasonally: a high yield was obtained from June to July, corresponding to the rainy season, and lowest yield was observed at August, corresponding to highest summer temperatures. The monthly average of dry matter yield was about 37.6g/m^2. The fresh matter produced during the high-yield period had watery tissues whereas it had low moisture tissues during the low-yield period 2. Nitrogen (N) uptake The average content of N was 2.3%, although the values over one-week intervals fluctuated from 1.3 to 3.5%. N increased at lor 2 weeks after the dressing of additional fertilizer, but decreased after 3 weeks. The monthly uptake per area during May to the end of September averaged 0.87g/m^2, and the total uptake was 4.2g/m^2. These amounts are low in comparison to those for general vegetables. 3. Phosphate (P_2O_5) uptake. The average content of phosphate was 1.72% with low fluctuations compared with the other elements. The monthly average uptake per area was 0.65 g/m^2 and the total uptake was 3.28 g/m^2, which was the lowest among the three elements. 4. Potassium (K_2O) uptake. The average content of potassium was 2.03%, with wide fluctuations similar to nitrogen. The content tended to decrease after August. The monthly average uptake per area was 0.76 g/m^2, decreasing after August, and the total uptake was 3.81 g/m^2. 5. Effective rate of three major elements in fertilizers. In the turf, 3.325 g/m^2 of N, 3.850 g/m^2 of P_2O_5 and 0.875 g/m^2 of K_2O were applied totally during May to September. The total uptake amounts of these three elements were reported above. Effective rates of applications of the three elements in fertilizers were calculated from these data: N=26.2%; P_2O5=16.8%; and K2O=87.5%. The effective rate of N was very low and so about 74% of applied N flowed out of the rhizoshere soil (and therefore polluting groundwater). The effective rate of P_2O_5 was the lowest among the three elements and so about 83% of applied P_2O_5 was unabsorbed by turf glass. But the lower layer of the turf ground that has high Phosphate retention should adsorb the unabsorbed P_2O_5. The effective rate of K_2O was very high and exceeded 100% at times, indicating the occurrence of luxury absorption.

芝生管理方法と芝草の養分吸収の関係について : バミューダーグラスとケンタッキーブルーグラス混植芝生

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