播期和密度对棉花叶柄和根系硝态氮含量的影响

为探讨大田棉花氮代谢随播期和密度的变化规律,选用华棉3109(G.hirsutum L.)于2014年在华中农业大学试验农场,采用裂区设计:播期(月-日)(S1,05-30;S2,06-14)为主区,密度(株·m-2)(D1,7.5;D2,9.0;D3,10.5)为副区,研究了硝态氮含量在主茎叶柄和根系的分布特点。结果表明:1)随生育进程推进,叶柄和根系硝态氮含量先升高后降低,初花期最高。2)主茎叶柄硝态氮含量随叶位变化,蕾期、初花期由上而下逐渐降低,第1叶最高;盛花期逐渐增高,第1叶和第4叶最高;不同生育时期棉花叶柄硝态氮含量在叶位间的下降幅度随播期推迟而降低,随密度增加先升高后降低。3)播期和密度对不同生育时期棉花叶柄和根系硝态氮平均含量的交互作用均显著,但播期和密度主效应影响不同:见花施肥前,随推迟播期,棉花叶柄硝态氮平均含量显著降低了42.9%,根系硝态氮平均含量显著升高了12.1%,增加密度对叶柄和根系硝态氮平均含量无显著影响。见花施肥后,随播期的推迟,叶柄硝态氮平均含量无显著性变化,初花期平均为5.05 mg·g-1,盛花期平均为2.62 mg·g-1;而根系硝态氮平均含量,初花期S1S2,盛花期S1S2;随密度增加,D1,D2与D3初花期叶柄和根系硝态氮平均含量均显著降低;盛花期叶柄硝态氮平均含量呈先升高后降低趋势变化,而根系硝态氮平均含量则与初花期相反,呈显著递增趋势。综上所述,晚播高密条件下,见花一次施肥后,推迟播期不改变棉花地上部叶柄硝态氮平均含量水平,适度增加密度有利于棉花叶柄维持较高的硝态氮含量,有利于为叶片氮代谢提供充足的底物。

Nitrate Content Distributions in Petioles and Roots of Cotton Affected by Sowing Date and Planting Density

To understand the effects of the sowing date and planting density on cotton nitrogen metabolism under late and direct seeding, a field split-plot design with sowing date (S1: 30^th May and S2: 14^th June) as the main plot and density (plants·m^-2) (D1: 7.5, D2: 9.0 and D3: 10.5) as the subplot, was used to measure the nitrate content dynamics in petioles and roots. The results showed the following: 1) the cotton nitrate contents in petioles and roots were first bloom period>peak bloom period>squaring period; 2) the cotton petiole nitrate content decreased in leaf sites from the top (with the highest value at the 1^st leaf) to the bottom during the squaring and first bloom periods, increased gradually in the central leaf sites (with the highest values at the 1^st and 4^th leaf) during the peak bloom period, and then declined from the top to second leaf site as the sowing date was delayed. The contents also initially rose and then dropped as the planting density increased; and 3) although significant interaction effects were observed on the average nitrate contents in petioles and roots during different periods, the main effects of sowing time and density differed. Before the first flower's fertilization (squaring), the average nitrate content in cotton petioles from top to bottom decreased by 42.9%, while the content in cotton roots significantly increased by 12.1% as the result of late sowing. Density had no significant effects on the average nitrate contents in cotton petioles and roots. After the first flower's fertileization (first bloom and peak bloom), due to the delay in the sowing date, no significant differences were observed between the average petiole nitrate contents of 5.05 mg·g^-1 and 2.62 mg·g^-1 at first and peak bloom, respectively. However, the average root nitrate content in S1 plants was significantly higher than that in S2 plants during first bloom period, which was opposite of the peak bloom results. Compared with first bloom period at D1, the average petioles and root nitrate contents significantly decreased up to 14.3% and 30.8%, respectively, at D2 and up to 16.6% and 29.2%, respectively, at D3 as the planting density increased. However, during peak bloom period, the average nitrate content in the petioles at D2 was significantly higher than those at D1(11.1%) and D3 (23.3%), whereas the trend in the average nitrate content in roots was contrary to that in first bloom period. In conclusion, under late sowing and higher density conditions, after fertilizer application at the first flower period, delayed sowing did not alter the average nitrate content in the main leaf petioles, while the optimum planting density resulted in a higher than average nitrate content being stored in the main leaf petioles, contributing to the sufficient supply of substrate for leaf nitrate metabolism.