Abstract

Nitrogen (N) is the mineral nutrient required in greater quantities by plants with deficiencies affecting crop production. Nitrate (NO₃^-) and ammonium (NH₄⁺) are the inorganic N forms most readily available for plant uptake. We investigated the influence of ammonium and nitrate rates on growth, nutritional status, chlorophyll production, and nutritional efficiency in mahogany seedlings, grown in an Oxisol soil under greenhouse conditions. Treatments were five N rates (50, 100, 150, 200, and 400 mg dm⁻³ N) in ammonium and nitrate forms and control treatment (0 mg dm⁻³ N), in a factorial design with five replications. The plants were harvested for evaluation at 150 days after transplanting. N supply affected mahogany growth, mainly in the production of leaf tissue. The maximum economic efficiency of N rates for production of leaf tissue was around 190 mg dm⁻³ N. The ammonium supply enhanced leaf tissue production, with a 20% increase in leaf area and 15% in leaf dry matter compared to nitrate. Furthermore, the plants showed a preference for ammonium uptake in rates above 200 mg dm⁻³ N, which indicates that the preference for N form was dependent on the concentration of N in the soil. The ammonium supply enhanced nutritional status, mainly phosphorus, demonstrating high synergism on uptake of this nutrient. Conversely, a strong antagonism between nitrate and phosphorus uptake was observed. Thus, ammonium enhanced the growth and nutritional status of mahogany seedlings and must be prioritized in its fertilization.

摘要

氮（N）是植物需要的大量矿物质营养素，其不足会影响作物的生产。硝酸盐（NO ₃ ^- ）和铵（NH ₄ ⁺）是无机氮形式最容易获得用于植物吸收。我们调查了铵和硝酸盐比率对在温室条件下在Oxisol土壤中生长的桃花心木幼苗的生长，营养状况，叶绿素生成和营养效率的影响。处理方式为铵和硝酸盐形式的五种氮肥（50、100、150、200和400 mg dm ^-3 N）和对照处理（0 mg dm ^-3）N），在具有五个重复的析因设计中。移植后150天收获植物用于评估。氮供应影响桃花心木的生长，主要在叶片组织的生产中。氮的最大经济效益是生产叶片组织的氮效率约为190 mg dm ^-3N。铵的供应提高了叶片组织的产量，与硝酸盐相比，叶片面积增加了20％，叶片干物质增加了15％。此外，植物表现出对铵吸收的偏好，其吸收速率高于200 mg dm ^-3N，表明对N形态的偏好取决于土壤中N的浓度。铵的供应增强了营养状况，主要是磷，显示了在吸收这种营养素方面的高协同作用。相反，观察到硝酸盐和磷吸收之间的强烈拮抗作用。因此，铵提高了桃花心木幼苗的生长和营养状况，必须优先施肥。