Effects of N Fertilization on the Growth and Yield of Two Maize Hybrids

Abstract

A single-cross maize hybrid, Tainung No. 351, and a double-cross hybrid, Tainan No. 11, were grown in the field at a density of 58,800 plants/ha in the fall of 1983. N rates of 75, 150, 225 and 300 kg/ha were supplied in the form of ammonium sulfate. Samplings were made at a two-week interval starting from mid-silking to maturity. Leaf area and N and total nonstructural carbohydrate (TNC) concentrations were determined in plant fractions. The purposes of this study were to compare the physiological differences between the two hybrids and to clarify the physiological basis of the high yield potential of Tainung No. 351. Results showed that increased N fertilization delayed the dates of heading and silking. Grain yield of Tainung No. 351 increased with increasing N level, due mainly to higher kernel number per ear which could compensate for the loss of lower 100-kernel weight. N had positive effects on plant N concentration, leaf area and dry matter accumulation. N use efficiencies (unit grain yield per unit N supplied) of Tainung No. 351 were 90.5 and 27.3 at N rates of 75 and 300 kg/ha, respectively. Corresponding values for Tainan No. 11 were 68.9 and 19.9. Yield efficiencies (unit grain yield per unit leaf area) were 3.06 and 2.96 g/dm2 for Tainung No. 351 and 3.50 and 3.17 g/dm2 for Tainan No. 11 at N rates of 150 and 300 kg/ha, respectively. Within 2 weeks after silking, stalk and cob acted as temporary sinks to store N and TNC for the subsequent needs of grain filling. TNC concentration was above 13% in the stalk of mature Tainung No. 351 plants but was below 3% in Tainan No. 11. This fact indicated that carbohydrate translocation of the high-yielding Tainung No. 351 was less efficient. Yield could be further enhanced through increasing kernel weight. Limiting factors to grain yield of Tainan No. 11 were presumed to be both source capacity and sink size. Experimental results suggested that nutritional requirements of Tainung No. 351 was high. Appropriate dense planting might be a good measure under satisfactory conditions to increase leaf area and photosynthetic ability. Further understanding of the interaction between N and C metabolism was important in order to increase kernel number and kernel weight simultaneously and hence the yield of Tainung No. 351. 試驗採用單雜交玉米品種臺農351 號與雙雜交品種臺南11 號為材料，於1983 年秋作在田間栽培，密度為每公頃58,800 株，氮肥用量為75、150、225與300 kg/ha；於玉米吐絲（mid-silking）期開始每隔 2 週取樣一次，測度葉面積與植株各器官氮素及非構造性碳水化合物（TNC）濃度變化，並調查產量性狀，目的在比較兩個玉米對氮素反應的生理性差異，以及探討臺農 351 號高產的理論基礎。試驗結果發現增加氮肥用量可延遲抽穗與吐絲日期，提高臺農351 號種子產量，但臺南 11 號之產量卻以 150 kg-N / ha 處理最高；產量提高的主要原因為一穗粒數增加，足以補償粒重降低的損失而有餘。在75 與300 kg-N / ha 處理時，臺農351 號的氮利用效率（產量／施用氮量）為90.5 與27.3，較臺南11 號之68.9 與19.9 為高；但於150 與300 kgN / ha 處理，臺南 11 號的產量效率（產量／單位葉面積）為3.50 與3.17g / dm2，遠較臺農351 號之3.06 與2.96 g/dm2為高，各器官氮素濃度有隨施氮量增加而提高的趨勢，且於種子充實期間大幅下落。莖與穗軸在吐絲後2 週內具有暫時貯存氮素與TNC 的功能，可供應隨後種子發育的需要。吐絲以後臺南11 號莖稈內TNC 濃度較臺農351 號為高，但下降之時間較早，幅度亦大；成熟時臺農 351 號莖稈內仍含有13％以上的 TNC，但臺南 11 號僅為 3%以下，顯示前者雖為高產品種，但粒重未臻理想，應謀增加粒重而更提高產量；後者之供源（source）能力與積儲（sink）容量均有不足，可能並為產量限制因子。試驗結果認為臺農351 號玉米品種對營養要素的需求量較高，建議栽植密度宜適量提高，以增加葉面積與生產乾物質能力，對氮素與碳素間相互作用的關係亦應再予瞭解，以求在同時增加粒數與粒重的情形下達到更高產的目標。