G Selassie Yihenew, Molla Eyayu, Muhabie Dinku, Manaye Fentanesh, Dessie Demelash
Department of Natural Resources Management, College of Agriculture and Environmental Sciences, Bahir Dar University, P. O. Box 5501, Bahir Dar, Ethiopia.
Amhara National Regional State Environment, Forest and Wildlife, Protection and Development Authority, Bahir Dar, Ethiopia.
Heliyon. 2020 Dec 7;6(12):e05629. doi: 10.1016/j.heliyon.2020.e05629. eCollection 2020 Dec.
Potassium (K) has been considered as a non-deficient nutrient in most Ethiopian soils. However, some studies recommended K application to K sufficient soils if K/Mg ratio is < 0.7. To resolve this controversy, field experiments and laboratory soil analysis were conducted in two districts (Yilmana Densa and Dera) in north-western Ethiopia on Mollic Nitisols (aric, humic) (pH = 5.5), Pellic Vertisols (aric, gilgaic, mazic) (pH = 6.2) and Vertic Luvisols (aric, nitic) (pH = 5.2) using wheat, and maize, respectively as test crops. The field experiments were laid out in a randomized complete block design with 7 K fertilizer rates (0, 42, 83, 125, 166, 208, and 249 kg ha K) and four replications. KCl and DAP (200 kg ha) fertilizers were added at planting. Urea (200 kg ha) was added in split, half at planting and half at tillering for wheat and ; and at knee-height stage for maize. Soil samples were taken two weeks after planting to determine K and Mg contents, K critical levels and optimum K/Mg ratio. The ammonium acetate extraction method was used to determine the K and Mg contents in the soil using a flame photometer and an atomic absorption spectrometer, respectively. Yield data were collected after harvest. The results of the study indicated that Mollic Nitisols (aric, humic), Pellic Vertisols (aric, gilgaic, mazic) and Vertic Luvisols (aric, nitic) had high K contents of 351, 380 and 434 mg kg, respectively. Rising K fertilizer levels increased soil K contents; however, this did not significantly increase crop yields. Mg contents were also in high category (>351 mg kg). The K/Mg values ranged from 0.60 to 0.80 in Mollic Nitisols (aric, humic), 0.70 to 0.88 in Pellic Vertisols (aric, gilgaic, mazic) and 0.71 to 1.04 in Vertic Luvisols (aric, nitic), and the values increased with an increasing K rates. However, wheat, and maize grain yields showed an increasing trend up to K/Mg ratio of 0.71 in Mollic Nitisols (aric, humic), 0.78 in Pellic Vertisols (aric, gilgaic, mazic) and 0.88 in Vertic Luvisols (aric, nitic), respectively, and declined above these values.
在大多数埃塞俄比亚土壤中，钾（K）一直被认为是一种不缺乏的养分。然而，一些研究建议，如果钾/镁比例小于0.7，即使土壤钾含量充足，也应施用钾肥。为了解决这一争议，在埃塞俄比亚西北部的两个地区（伊尔马纳·丹萨和德拉），分别以小麦和玉米作为试验作物，对变性土（潮湿、腐殖质）（pH = 5.5）、粘质变性土（潮湿、强石灰性、中壤质）（pH = 6.2）和粘化淋溶土（潮湿、强酸性）（pH = 5.2）进行了田间试验和实验室土壤分析。田间试验采用随机完全区组设计，设置7个钾肥施用量水平（0、42、83、125、166、208和249 kg/ha K），重复4次。种植时添加氯化钾和磷酸二铵（200 kg/ha）肥料。尿素（200 kg/ha）分施，小麦在种植时和分蘖期各施一半，玉米在拔节期施一半。种植两周后采集土壤样本，以测定钾和镁含量、钾临界水平和最佳钾/镁比例。分别使用火焰光度计和原子吸收光谱仪，采用醋酸铵提取法测定土壤中的钾和镁含量。收获后收集产量数据。研究结果表明，变性土（潮湿、腐殖质）、粘质变性土（潮湿、强石灰性、中壤质）和粘化淋溶土（潮湿、强酸性）的钾含量分别较高，为351、380和434 mg/kg。钾肥施用量增加会提高土壤钾含量，但这并未显著提高作物产量。镁含量也处于较高水平（>351 mg/kg）。变性土（潮湿、腐殖质）的钾/镁值在0.60至0.80之间，粘质变性土（潮湿、强石灰性、中壤质）在0.70至0.88之间，粘化淋溶土（潮湿、强酸性）在0.71至1.04之间，且这些值随钾肥施用量的增加而增加。然而，小麦和玉米籽粒产量分别在变性土（潮湿、腐殖质）的钾/镁比例达到0.71、粘质变性土（潮湿、强石灰性、中壤质）达到0.78、粘化淋溶土（潮湿、强酸性）达到0.88之前呈上升趋势，超过这些值后则下降。
