Crop response to phosphorous (P) application is often erratic in most soil types in the world. In alkaline calcareous soils, P retention and mobilization take place due to precipitation and adsorption. P adsorption isotherms are the powerful tools for assessing optimum P levels for different crops and soils. Laboratory and field studies were carried out to evaluate P sorption capacity in a highly calcareous soil and corresponding fertilizer levels for yielding 0.1 to 1.0 mg P L−1 of soil solution. Although Freundlich adsorption isotherm model showed a better fit than Langmuir model, P fertilizer levels used in the field, ranging from 20 to 150 kg P2O5 ha−1, were based on Langmuir model to yield the estimated P solution. Moreover, nitrogen (N) and potassium (K) were applied at the rates of 120 and 60 kg ha−1 as urea and potassium sulfate (K2SO4), respectively, in a basal treatment at the time of sowing. Grains per spike, 1000-grain weight, grain yield, spike length, and biological yield were increased as the level of P increased, but the non-significant differences among 90, 100, and 120 kg P2O5 ha−1 for most of the above parameters suggested that the former rate could be the maximum level for wheat fertilization in the calcareous soil. Similarly, plant N, P, and K were increased with application of P, but non-significant differences were observed from doses 90 to 120 kg P2O5 ha−1. Moreover, the rate of 90 kg P2O5 ha−1 could yield 0.6 mg P L−1 of soil solution as per Langmuir adsorption isotherm model, while as per Freundlich model, this value could reach only 0.3–0.4 mg P L−1, which is close to the published literature. It is concluded that Freundlich adsorption isotherm is more suitable to be used for the calculation of phosphatic fertilizer rate and its adsorption capacity in the given soil than Langmuir adsorption isotherm.

中文翻译：

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使用吸附等温线模型优化钙质土壤中生长的小麦中的磷含量

在世界上大多数土壤类型中，作物对磷 (P) 施用的反应通常是不稳定的。在碱性钙质土壤中，由于沉淀和吸附而发生磷的保留和迁移。P 吸附等温线是评估不同作物和土壤的最佳 P 水平的有力工具。进行了实验室和田间研究以评估高钙质土壤中的 P 吸附能力和相应的肥料水平，以产生 0.1 至 1.0 mg PL-1 土壤溶液。尽管 Freundlich 吸附等温线模型显示出比 Langmuir 模型更好的拟合，但田间使用的磷肥水平范围为 20 至 150 kg P2O5 ha-1，基于 Langmuir 模型以产生估计的 P 溶液。此外，氮 (N) 和钾 (K) 以 120 和 60 kg ha-1 的比例作为尿素和硫酸钾 (K2SO4) 施用，分别在播种时进行基础处理。每穗粒数、千粒重、籽粒产量、穗长和生物产量随着磷水平的增加而增加，但对于上述大部分情况，90、100和120 kg P2O5 ha-1之间的差异不显着参数表明，前者可能是石灰质土壤中小麦施肥的最高水平。类似地，植物 N、P 和 K 随施磷而增加，但在 90 至 120 kg P2O5 ha-1 的剂量下观察到非显着差异。此外，根据 Langmuir 吸附等温线模型，90 kg P2O5 ha-1 的比率可以产生 0.6 mg PL-1 土壤溶液，而根据 Freundlich 模型，该值只能达到 0.3-0.4 mg PL-1，接近到已发表的文献。