Vol. 17(4), pp. 629-641, April, 2021 DOI: 10.5897/AJAR2021.15463 Article Number: CC4BE3B66609 ISSN: 1991-637X Copyright ©2021 African Journal of Agricultural Author(s) retain the copyright of this article http://www.academicjournals.org/AJAR Research Full Length Research Paper Nutrients balance approach with emphasis on base cations and ratios concepts as a decisions-support tool in optimizing fertilizers use Assefa Menna Debre Zeit Agricultural Research Center, Ethiopian Institute of Agricultural Research (EIAR), P. O. Box - 2003, Addis Ababa, Ethiopia. Received 21 January, 2021; Accepted 16 March, 2021 Thirty-six soil samples collected from 24 sites were used to investigate the relationships between cation-ratio concepts and sufficiency level approaches in plant nutrition. Based on threshold values, about 25.0% of the soils had calcium:magnesium (Ca:Mg)-ratio fallen outside developed favorable range, despite the sufficient levels of individual elements in soils, violating the base cation ratio concept. Similarly, 63.0% of soils had potassium:magnesium (K:Mg)-ratio falling in the unfavorable range for K uptake, though individual element K was found to be above adequate in all sites/soils. In 29.0% of soils, (Mg:K)-ratio is rated unfavorable for nutrients’ uptake, the directly level to sufficiency level concepts. Likewise, all soils had the % K:TEB (total exchangeable bases)-ratio falling within the suggested fav orable range for the most tropical crops, favoring the two concepts. With respect to Ca:TEB ratios, 79.0% of soils were considered unfavorable for Mg and/or K uptake, implying that the lower the base saturation, more favorable the conditions for the aforementioned nutrients uptake and vice-versa. This is also against the base cations’ saturation ratio concept because all soils in those sites had low levels of Ca and Mg. In conclusion, therefore, from such contradictory information, those generated the validity of the base cations’ ratio concept need further detailed investigation. Key words: Potassium, calcium, magnesium, ratios, fertilizers, rhizosphere. INTRODUCTION Sharply rising human population and associated factors (Hurni et al., 2010). Indeed, this is a continuous process have degraded the natural resource base, the soil, thus affecting food and nutrition security in the country. For threatening sustainable agriculture in Ethiopia. In this example, some Vertisols in the central Ethiopian country, soil/land degradation is mainly due to intensive agricultural lands have problems of phosphorus (P) and cropping, overgrazing and unsustainable land-use and related nutrients fixing characteristics. Many were also tenure systems, which further aggravated the loss of soil reported to be poor in essential plant nutrients and quality. Among the soil degradation processes, nutrients organic carbon (OC) (Menna, 2017, 2018, 2019). unavailability or depletion and imbalances; and the In our previous research works, soil-testing combined reduction in total and biomass carbon are the major ones with crop response data primarily have been used as a E-mail: [email protected]. Tel: (+251) 912006149. Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License 630 Afr. J. Agric. Res. decision-support tool in optimizing nutrients management. pre-soil testing, but on areas approximately 0.5 to 1.5 miles away With regard to soil-testing two general principles were from first season(s) S responsive sites, Do1, Bk1 and BT1, evolved. The major one was the Crop Nutrient respectively. In both seasons, randomized complete block design Requirement/ Sufficient Level of Available Nutrient (RCBD) was used and was replicated three times. All soil samples were taken from 10 spots per block, bulked and further composted (CNR/SLAN) concept, which was built on the concept to make a composite sample per farmer field and/or soil depths. that there are certain levels of plant nutrients in soils that The disturbed samples were then air-dried immediately in dry- 2- can be defined as optimum. Below those defined levels, rooms to avoid SO4 formation from organic matter (OM) in transit, crops will respond to the application of nutrient in ground and sieved to pass through 1-mm sieve. Then, duplicate question. The other was the Base Cation Saturation Ratio analysis was made for different soil variables using wet chemistry (BCSR), which promotes the concept that maximum yield laboratory (Labs) at Sokoine University of Agriculture (SUA), Tanzania and Holeta and Debre Zeit research centers (EIAR), can only be achieved by creating an ideal ratio of calcium Ethiopia as per the methods outlined in Table 1. Finally, the cation (Ca), magnesium (Mg), potassium (K) and sodium (Na) in ratios were calculated using the respective variables. Micro- soils. A more detailed discussion of the two approaches nutrients copper (Cu), manganese (Mn), iron (Fe), zinc (Zn), boron was based on the works by Eckert (1987). In fact, the (B) and molybdenum (Mo) were also considered. base saturation and ratios concept were based on much earlier works provided by Hunter et al. (1943), Bear and Toth (1948), and Hunter (1949). According to Bear et al. RESULTS AND DISCUSSION (1945) for ideal soil it was suggested that, the bulk of exchangeable complex should be occupied by Ca, Mg, K Tables 2 to 4 present the selected physico-chemical and hydrogen (H). However, this was later relaxed by variables of the studied soils. As presented, the studied Graham (1959). About 20 years later, Baker and soils varied in their properties, which could be peculiar to Amacher (1981) defined normal values as 60 to 80% for the specific AEZs. The upcoming discussions focus on Ca, 10 to 20% for Mg and 2 to 5% for K. the percent saturation, ratios concepts and related soil Based on these general descriptions, therefore, the aim properties that are assumed to guarantee high yields and of this research work was (1) to assess the concept of crop quality. BCSRs and (2) to see the relationships between SLAN and BCSR approaches in the studied soils. The study also aimed at looking at the relationship between some Major cations and some basic ideas soil variables and wheat yield at native soil conditions. It 2+ is hypothesized that a strong-positive relationship The cations used in largest amounts by plants are Ca , + 2+ between the SLAN and BCSR concepts would exist. K and Mg , which exist in the soil solution in the form of ions. Cations are absorbed from the soil solution (thin film of water around plant roots, root hairs and soil particles) MATERIALS AND METHODS by actively growing plants. The exchange sites are Site selection negatively charges associated with clay sized particles, and some of the soil organic matter (SOM). The cations In the present investigation, soil samples collected from 24 sites, in at the exchange site are in equilibrium with those in the three representative locations in central Ethiopian agricultural lands, soil solution. The number of negative charges can be namely Arsi (Ar), East-Shewa (ES) and West-Shewa (WS) zones were considered. The three study areas were selected and geo- measured analytically and is referred to as the cation referenced using Global Positioning System (GPS-GARMIN; model exchange capacity (CEC). It is widely recognized that, number GPS-60) assisted by Google earth (2011), and were the availability of nutrients for plant uptake does not classified by elevation and agro-ecological zones (AEZs) and soil- depend only on their absolute levels, but also on the type when known. The sites, then, were used for conducting 24 relative amounts of individual elements and different base sulfur (S) response and/or S rate determination experiments in wheat or faba bean. The specific locations and salient features of cation ratios in soils. Indeed, percent saturation and the selected sites are presented in Figure 1. electrical conductivity (EC) of the studied soils were assumed to have direct relationships with the pH. Soil sampling, preparation and analysis The first 18 surface soil samples (0-20 cm soil depth) were Soil physico-chemical properties collected before planting each of the 18 sulfur (S) response experiments (2013-2014). Similarly, the other 18 soil samples were The studied soils showed important variations in the collected from 0-20 cm, 20-40 cm and 40-60 cm soil depths at each physico-chemical variables and nutrient contents. site in season-II (2015-2016) before planting the test crop(s) Exchangeable-Al was detected in strongly acidic soils (Tables 2 to 4). The three fields, namely GS2, Ke2 and NS2 in season-II, were and this was positively correlated with Ca and Mg selected based on the experimental conditions in seasons-I. deficiency, which may necessitate the application of Ca Whereas, WG/Do2, Bk2 and BT2 were selected randomly without and Mg containing fertilizers or liming in those sites. All Menna 631 Figure 1. Locations map showing study site-fields in Arsi, East- and West-Shewa zones of central Ethiopia. 1 = Abosara Alko (AA); 2 = Dosha (Do1); 3 = Gora Silingo (GS1 or 2); 4 = Chefe Misoma (CM); 5 = Boneya Edo (BE); 6 = Boro Lencha (BL); 7 = Chefe Donsa (CD); 8 = Keteba (Ke1); 9 = Ude (Ud); 10 = Bekejo (Bk1); 11 = Insilale (In); 12 = Kilinto (Ki); 13 = Nano Kersa (NK); 14 = Nano Suba (NS1); 15 = Berfeta Tokofa (BT1); 16 = Dawa Lafta (DL); 17 = Wajitu Harbu (WH); 18 = Tulu Harbu (TH: 1st season); 19 = Wonji Gora (WG/Do2); 20 = GS2; 21 = Ke2; 22 = Bk2; 23 = NS2; and 24 = BT2 (2nd season). The numbers (1) and (2) indicate the information which was generated in 1st and 2nd seasons, respectively and soil-type when known. the soils were salt-free or had no sodicity problems. But, and Ca were found to be limiting depending on the AEZs the exchangeable aluminium (Al3+) was detected in and pH of soils.