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No.22 (1975/12) >

 
Title :窒素およびりん酸施用量と秋植サツマイモの養分吸収(農芸化学科)
Title alternative :Effects of applied nitrogen and phosphorus on nutrient uptake of sweet potato autumn crop grown on a calcareous clayey soil (Department of Agricultural Chemistry)
Authors :大屋, 一弘
Authors alternative :Oya, Kazuhiro
Issue Date :1-Dec-1975
Abstract :沖縄島に分布する灰褐色石灰質重粘土壌(ジャーガル)において窒素とりん酸の施用量が秋植サツマイモの窒素・りん酸・カリなどの吸収, および栽培跡地の窒素・りん酸・カリ含量におよぼす影響を調べる目的で実験を行なった。栽培実験を行なった土壌は琉球大学農学部農場(那覇市石嶺)の稲嶺統土壌で, 前報(9)の実験で得られたかずら, 塊根, 土壌サンプルなどを分析に供した。結果は次のとおりであった。収穫期(植付後5カ月目)のかずらの全窒素含有率は1.8∿2.2%の範囲にあり, 窒素およびりん酸の施用量によって影響は受けなかった。ただしかずらおよび塊根は窒素の増施によって収量が増加するのでそれに伴なって窒素吸収量が増加した。窒素吸収量は最大の場合でも施用窒素量(7kg N/10a)よりは少ないので施用窒素の大部分が作物に利用されていないと考えられた。栽培跡地土壌の全窒素含有率は表土で0.11∿0.14%, 心土で0.7∿0.12%であり, 栽培前の含有率と大差がなかった。またサツマイモ全植物体(かずら+塊根)によって吸収された窒素の量と栽培跡地の全窒素含有率との間には一定の関係がみられなかった。植付後5カ月目のかずらのりん酸含有率は窒素無施用の場合に0.91∿0.93%, 窒素多用(7kg N/10a)の場合に0.55∿0.58%であり, 窒素施用によりかずらのりん酸含有率は低下する傾向にあった。しかしりん酸施用量による影響は示されなかった。塊根のりん酸含有率は0.3∿0.4%で, 窒素とりん酸施用量の影警はみられなかった。サツマイモ全植物体によるりん酸吸収量は全ての処理区でりん酸施用量(3.5または7kg P_2O_5/10a)より少なかった。栽培跡地の表土の可給態りん酸含量は栽培前の含量と同じレベルであったが, 心土では処理区間に大きなばらつきがみられた。かずらのカリ含有率は植付後4カ月目で3∿3.5%, 5カ月目では2∿2.8%となり令による差が認められた。しかし窒素とりん酸施用量による影響はみられなかった。塊根のカリ含有率は1.2∿1.8%で, 窒素, りん酸などの施用量の影響, ならびに令による差は認められなかった。サツマイモ全植物体によるカリ吸収量は窒素施用量が多くなると増加しカリ施用量(7kg K_2O/10a)を上回った。栽培跡地の置換性カリ含量は表土, 心土ともに栽培前のレベルより低下した。今回の実験で得られたかずらの窒素吸収量, サツマイモ全植物体のりん酸およびカリ吸収量, および他のデータから推定される塊根の窒素吸収量などをもとにして, 秋植サツマイモの目標収量に対する窒素, りん酸, カリの必要施用量の指標図作成を試みた。
Chemical analyses were carried out in order to investigate effects of nitrogen and phosphorus applied at various amounts on the nitrogen, phosphoric acid and potash contents of the vine and root tuber of the sweet potato autumn crop obtained from the previous experiment by the author. The experiment had been done with applications of three levels of nitrogen (0,3.5,and 7kg N per 1/10 hector), two levels of phosphoric acid (3.5,and 7kg P_2O_5 per 1/10 hector), and a constant level of potash (7kg K_2O per 1/10 hector) to each crop of 1972 and 1973 on a calcareous clayey soil. The surface (0-20cm) and subsurface (40-50cm) soil samples were also analyzed for total nitrogen, 0.002N H_2SO_4-extractable phosphoric acid and NH_4OAc-exchangeable potassium in order to study their residual levels in the soils as affected by the applied fertilizer and crop uptake. The nitrogen content of the vine harvested five month after planting was in the range of 1.8 and 2.2% being received no effect of the applied nitrogen and phosphorus. Nitrogen of the root tuber was not analyzed, but its content was calculated as nearly constant (0.24%) from other available data for estimation of nitrogen absorption by the crop. The amount of nitrogen absorbed by the vine and root tuber increased because the crop increased in the yield as the applied nitrogen increased from 0 to 7kg per 1/10 hector. It was 6.4kg at the highest but still less than the applied amount. There was no clear tendency of decrease in the total nitrogen of the soils as affected by the nitrogen uptake of the crop. The total nitrogen ranged from 0.11 to 0.14% in the surface soil and from 0.70 to 1.2% in the subsurface soil, where the original levels were 0.10 and 0.11%, respectively. I
It, therefore, was assumed that some nitrogen had become unavailable to the crop. The experiment suggested necessity of further studies on the nitrogen's traces. The phosphoric acid content of the vine was not affected by the applied phosporus, but showed a decrease from about 0.9 to nearly 0.6% when nitrogen application increased from 0 to 7kg per 1/10 hector. The phosphoric acid content of the root tuber was in a narrow range of 0.3 and 0.4% showing effect of neither nitrogen nor phosphorus applied. The sweet potato (vine+root tuber) absorbed 2.4kg of phosphoric acid at the highest but still less than the applied amounts (3.5 or 7kg P_2O_5 per 1/10 hector). The level of 0.002N H_2SO_4-extractable P_2O_5 in the surface soil after croping was nearly same with the level before croping (3.1mg P_2O_5 per 100g), but in the subsurface soil it varied from treatment plot to plot indicating no definite tendency of increase or decrease. No effect of the applied nitrogen and phosphorus was observed on the potash content of the vine but the vine showed a difference in the potash content by crop age, that is, 3.0 to 3.5% potash in the vine at four month after planting but 2.0 to 2.8% at five month. Effect of the variable fertilizer applied was not indicated on the potash content of the root tuber which ranged from 1.2 to 1.8%. Neither was effect of the crop age. The surface and subsurface soils were slightly lower in the content of NH_4OAc-exchangeable potassium than the soils before croping which contained 0.54 and 0.31me K per 100g, respectively. The sweet potato (vine+root tuber) increased in the uptake of potash as the yield was promoted by the applied nitrogen. The potash uptake of the crop reached 10kg per 1/10 hector exceeding the applied amount of 7kg. A diagrammatic index was proposed from the present study to practise expedient fertilization for a higher yield of the sweet potato autumn crop in relation to maintaining better fertility of the soil.
Type Local :紀要論文
ISSN :0370-4246
Publisher :琉球大学農学部
URI :http://hdl.handle.net/20.500.12000/4331
Citation :琉球大学農学部学術報告 = The Science Bulletin of the Faculty of Agriculture. University of the Ryukyus no.22 p.191 -202
Appears in Collections:No.22 (1975/12)

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