Table 3_Soybean yield, nutrient use efficiency, and economic returns of phosphorus and potassium in Ghana’s interior savanna.docx

IntroductionPhosphorus (P) and potassium (K) deficiencies are increasingly being reported in Ghana’s interior savanna soils. Smallholder farmers consider soybeans as a “zero-input” crop resulting in low yields and profitability. Studies indicate a positive response to P application; however, knowledge of the synergistic effect of P and K in soybeans is limited. A six-site year experiment was conducted to evaluate the synergy of P and K for soybean yield, partial factor productivity (PFP), agronomic efficiency (AE), rain-use efficiency (RUE), and variable-cost ratio (VCR).
Materials and methodsThe treatments were 4 × 4 factorial combinations of P at 0, 25, 50, and 100 P2O5 (kg ha−1) and K at 0, 25, 50, and 100 K2O (kg ha−1), and their combinations laid out in a randomized complete block design with four replications. The soybean cultivar “Favor” (TGx 1844–22E), released and registered by the Savanna Agricultural Research Institute (SARI), was used as the test crop.
Results and discussionFlowering time was reduced at Nyankpala and Dokpong by 0.2 and 0.4 (days), while plant height was increased by 4%–18% over control. Yield and RUE increased as P and K rates increased, with the greatest yield from T15 (P100K50) in Manga (2.34 t ha−1) and Nyankpala (2.37 t ha−1), T16 (P100K100) at Dokpong (2.68 t ha−1), and RUE from T15 across locations. The PFP, AE, and VCR values decreased with increasing P and K rates, with the greatest PFP, AE, and VCR from T5 (P25K0) at Manga and Dokpong and T2 (P0K25) at Nyankpala. All treatments exceeded the VCR > 2.0 threshold, except T12 (P50K100) across locations, and T16 at Manga and Nyankpala. The greatest economic returns are T5 at Manga and Dokpong and T2 at Nyankpala.
ConclusionBy all indications, the study justified the use of nutrient input in soybeans of P and K to enhance grain yield and profitability. Avoiding broadcast applications and adopting precision placement using the 4R nutrient principles of right placement, right fertilizer source, right rate, and the right time is key. The study recommends further experiments on different combinations of P and K in a long-term residual study.

引言 磷（P）与钾（K）缺乏症在加纳内陆稀树草原土壤中的报道日益增多。小农将大豆视为“零投入”作物，导致产量与种植收益低下。已有研究表明，施加磷肥对大豆具有正向增产效果，但学界关于磷钾配施的协同效应的认知仍较为有限。本研究开展了6个站点年的田间试验，旨在评估磷钾配施对大豆产量、偏生产力（partial factor productivity, PFP）、农艺效率（agronomic efficiency, AE）、雨水利用效率（rain-use efficiency, RUE）及可变成本比率（variable-cost ratio, VCR）的影响。

材料与方法 试验设置4×4因子组合处理：磷肥施用量设为0、25、50、100 kg P₂O₅ ha⁻¹四个梯度，钾肥施用量设为0、25、50、100 kg K₂O ha⁻¹四个梯度，各组合采用完全随机区组设计，设置4次重复。供试大豆品种为“Favor”（TGx 1844–22E），由稀树草原农业研究所（Savanna Agricultural Research Institute, SARI）审定登记。

结果与讨论 在Nyankpala与Dokpong站点，大豆开花期分别缩短0.2天与0.4天，株高较对照组提升4%~18%。随着磷钾肥施用量的增加，大豆产量与雨水利用效率（RUE）均显著提升：Manga站点与Nyankpala站点的最高产量均来自处理T15（P100K50），分别为2.34 t ha⁻¹与2.37 t ha⁻¹；Dokpong站点的最高产量来自处理T16（P100K100），为2.68 t ha⁻¹；各站点的最高RUE均来自处理T15。偏生产力（PFP）、农艺效率（AE）与可变成本比率（VCR）则随磷钾肥施用量的增加呈下降趋势：Manga与Dokpong站点的最高PFP、AE、VCR均来自处理T5（P25K0），Nyankpala站点则来自处理T2（P0K25）。除跨站点的处理T12（P50K100）以及Manga和Nyankpala站点的T16外，所有处理的VCR均高于2.0阈值。经济效益最优的处理为Manga与Dokpong站点的T5，以及Nyankpala站点的T2。

结论 综合各项试验结果，本研究证实了为提升大豆籽粒产量与种植收益，需施加磷钾养分投入。生产中需避免肥料撒施，采用精准施肥方式，遵循4R养分管理原则：正确的施用位置、合适的肥料种类、适宜的施用量与正确的施用时机。本研究建议进一步开展长期定位试验，探究不同磷钾配施组合的后效。