Agronomic experiments were conducted on-farm under rain-fed conditions during two cropping seasons (2018 and 2019) in two sites: the experimental plot of the Institute of Agricultural Research for Development (IRAD), Babungo in the North-West region and the Teaching and Research farm of the Department of Agronomy at Bansoa in the West region, Cameroon. The growing period covered end-March to mid-September. Babungo is located between longitudes 15˚25'E and 15˚30'E and between latitudes 5˚4' and 5˚10'N and situated at an altitude of about 300 meters above sea level while Bansoa is located between longitude 10˚15'E and latitude 05˚25'N and situated at an altitude of about 1414 meters above sea level. The areas have mean monomodal annual rainfall and temperature of approximately 1600 mm and 27.2˚C for Babungo and 1936 mm and 20.4˚C for Bansoa respectively. The soil of Babungo which is sandy clay loam is broadly classified as umbric Cambisol while that of Bansoa is sandy loam and classified as ustic Oxisol [21] [22]. The results of soil analyses before the start of experiments showed that they were acidic, high in organic matter, low in total N and available P as shown in Table 1.

Plant material used in the study was maize composite seed variety (Cameroon Highlands Composite) CHC 202 with yellow flint due to its adaptability to acidic soil of the western highlands agro-ecological zone purchased from IRAD Dschang. According to inquiries with agronomist and farmers in the study areas, it is a variety of great agronomic performance since it is tolerant to leaf blights,

smuts, maize streak virus diseases and highland rust and can produce about 7 - 8 t/ha. It attains maturity at about 135 - 150 days. Organic and mineral fertilizers used were fresh leaves of Calliandra spp., Leucaena spp., Acacia spp. and Cassia spp. collected from already established fields at Ndop and Dschang, tertiary fertilizer composed of NPK (3 3 45), NPK (14 24 14) + 3.5 MgO and Urea purchased from agro-retailers in the study areas.

Analysis of variance was conducted using XLSTAT 2014 statistical software to compare treatment effects on maize yields. Means were separated using the student Newman keuls’ Test at 5% level (P ≤ 0.05). In order to conduct an economic analysis of the different treatments, partial budgeting analysis techniques was employed to evaluate the various costs and corresponding benefits of technologies used in the experiments.

The results of ANOVA indicated that maize grain yield varied significantly (P ≤ 0.05) among treatments on umbric Cambisol and ustic Oxisol and between soil types. However, the test used in mean separation (student Newman keuls’ Test) showed that there were no significant differences among sole biomass treatments as well as those combining leaf biomass and mineral fertilizer. Furthermore, the results over 2 cropping seasons showed that, 1½ t/ha Acacia + (50 N + 37.5 P₂O₅ + 45 K₂O) treatment gave the highest maize grain yield followed closely by 1 t/ha Calliandra + (50 N + 37.5 P₂O₅ + 45 K₂O) treatment with 5.93 and 5.80 t/ha respectively on umbric Cambisol, while 1½ t/ha Cassia + (50 N + 37.5 P₂O₅ + 45 K₂O) treatment gave the highest maize grain yield followed closely by1 t/ha Leucaena + (50 N + 37.5 P₂O₅ + 45 K₂O) treatment with 6.01 and 5.92 t/ha respectively on ustic Oxisol. The absolute control treatments gave minimum maize grain yield of 1.89 and 1.93 t/ha respectively under umbric Cambisol and ustic Oxisol. Between soil types, maximum maize grain yield (5.15 t/ha) was recorded on ustic Oxisol as shown in Table 3.

^a,b,c: comparison of maize grain yield and soil types on application of treatments over 2 years: means in a column and those on row of soil types having different letter(s) are significantly different (student Newman Keuls’ test at P ≤ 0.05). T₁: 2 t/h Calliandra; T₂: 2 t/h; Leucaena; T₃: 3 t/h Acacia; T₄: 3 t/h Cassia; T₅: 1 t/h Calliandra + (50 N + 37.5 P₂O₅ + 45 K₂O; T₆: 1 t/h Leucaena + (50 N + 37.5 P₂O₅ + 45 K₂O); T₇: 1½ t/h Acacia + (50 N + 37.5 P₂O₅ + 45 K₂O); T₈: 1½ t/h Cassia + (50 N + 37.5 P₂O₅ + 45 K₂O); T₉: 100 N + 75 P₂O₅ + 90 K₂O Kg/ha; T₁₀: Absolute control.

The results of the economic analysis varied according to the technology used in soil management practices. On the average across the two cropping seasons, 1½ t/ha Acacia + (50 N + 37.5 P₂O₅ + 45 K₂O) treatment recorded the highest net benefit and return to labor of 286,500 FCFA and 5.1 respectively on umbric Cambisol while 1½ t/ha Cassia + (50 N + 37.5 P₂O₅ + 45 K₂O) treatment recorded the highest net benefit and return to labor of 296,051 FCFA and 5.30 respectively on ustic Oxisol. These were followed closely by 3 t/ha Acacia and Cassia treatments with net benefit and return to labor of 286,000 FCFA and 4.90 respectively on umbric Cambisol and 296,041 FCFA and 5.10 respectively on ustic Oxisol. On the other hand, treatments that received 3 t/ha Acacia and Cassia gave maximum benefit to cost ratios of 2.84 and 2.92 respectively on umbric Cambisol and ustic Oxisol. The control treatments recorded the lowest net benefits, benefit to cost ratios and returns to labor of −78,500 FCFA, 0.00 and −1.60 respectively on both soils as shown in Table 4.

Grain yield is the final result of many complex morphological and physiological

T₁: 2 t/h Calliandra; T₂: 2 t/h;Leucaena; T₃: 3 t/h Acacia; T₄: 3 t/h Cassia; T₅: 1 t/h Calliandra + (50 N + 37.5 P₂O₅ + 45 K₂O; T₆: 1 t/h Leucaena + (50 N + 37.5 P₂O₅ + 45 K₂O); T₇: 1½ t/h Acacia + (50 N + 37.5 P₂O₅ + 45 K₂O); T₈: 1½ t/h Cassia + (50 N + 37.5 P₂O₅ + 45 K₂O); T₉: 100 N + 75 P₂O₅ + 90 K₂O Kg/ha; T₁₀: Absolute control.

processes taking place during the growth and development of crops [24]. The application of organics alone or in combination with mineral fertilizers led to increased maize grain yield compared to the control. Sole application of leaf biomass of Calliandra spp. and Acacia spp. (umbric Cambisol) and Leucaena spp. and Cassia spp. (ustic Oxisol) generated higher grain yields than the control treatments while the combination of leaf biomass of Calliandra spp. and Acacia spp. (umbric Cambisol) and Leucaena spp. and Cassia spp. (ustic Oxisol) and inorganic fertilizers generated higher grain yields than other treatments (Table 3). The higher yields from organic treatments could be attributed to positive effects of organic materials on soil physicochemical properties [14]. The differences in fertilizer technologies that generated higher yields on umbric Cambisol and ustic Oxisol might be related to their nutrient release patterns. These technologies might have released nutrients proportionately to crop demand during growth and development stages which led to greater maize yields. Soil characteristics might have influenced nutrient release patterns of organic residues added to the soil [23].

According to Huang et al. [8], the leafy pruning incorporated into the soil at the beginning of the season decomposed and released nutrients especially nitrogen, which enhanced crop performance and soil characteristics. The integration of organic and inorganic fertilizers might have resulted into synergy and improved synchronization between nutrient release and uptake by plants leading to higher yields [25]. According to Vanlauwe et al. [26] and Afe et al. [24], the production of grain yield might be due to better growth, development and dry matter accumulation with proper supply of nutrients to plant and increase in the availability of other plant nutrients with the respective source of nitrogen application or extra crop produce can often be observed due to positive direct or indirect interactions between fertilizer and organic inputs as suggested by Magda et al. [27]. The inorganic fertilizer provides most of the nutrients and the organic fertilizer increases soil physicochemical properties [17]. The findings of this study are similar with those of Mugendi et al. [28] who found that Leucaena biomass combined with mineral fertilizer gave higher crop yields as compared to sole use of mineral fertilizer or sole Leucaena biomass. These results corroborate with those of Mucheru-Munaet al. [18] who found that Leucaena and Calliandra biomass combined with mineral fertilizer gave higher maize yields as compared to sole use of inorganic fertilizer or Leucaena and Calliandra biomass. These results equally corroborate with those of Zhao et al. [29] who reported that farmyard manure combined with chemical fertilizer resulted in higher increase in maize yield. Similarly, Dilshad et al. [30] and Makinde and Ayoola [31] stated that high and sustainable crop yields are only possible with integrated use of mineral fertilizers with organic matter.

Maize plants in the control plots which did not receive any treatment but submitted under the same ecological conditions (light, amount of water, constant weeding and treatment of insecticides) showed low results as far as grain yields are concern. The relatively poor maize grain yields results in the control plots could be partly due to low doses of mineral elements compared to optimal doses used in the experimentation. It could equally be due to the absence of phosphorus in the soil as lack of phosphorus has been particularly identified as a factor limiting the growth of plants. Besides, Baraloto [32] showed that most tropical zones are situated on soils chemically poor, especially in phosphorus and nitrogen. Since the organic materials may often not be available in large amounts that are required for sole application, farmers are encouraged to adopt combined application of leaf biomass and inorganic fertilizers is a better option for increasing fertilizer use efficiency and providing a more balanced supply of nutrients and ultimate yield otherwise higher N and P application rates are required to attain better yield in maize [17] [33].

Averagely across the two cropping seasons, 1½ t/ha Acacia + (50 N + 37.5 P₂O₅ + 45 K₂O) treatmenton umbric Cambisol and 1½ t/ha Cassia + (50 N + 37.5 P₂O₅ + 45 K₂O) treatment on ustic Oxisol recorded the highest net benefit and return to labor. This could be due to higher yields obtained from positive direct or indirect interactions between fertilizer and organic inputs as suggested by Boukong et al. [22] or lower labor required compared to the sole applications [18]. This study equally showed thatall the treatments that received fertilizers were economically profitable as their benefit to cost ratios were greater than 2 but treatments with sole leaf biomass recorded the higher benefit to cost ratios compared to combined leaf biomass and inorganic fertilizers. This could be attributed to the fact that the cost of organic fertilizer and the labor cost of applying it was lowercompared to combined leaf biomass and inorganic fertilizers. These findings are similar with those of FAO [34], who reported that any treatment that receives fertilizer in an environment where water is not limiting is considered profitable only when its B/C ratio is equal to or greater than 2. These findings are in agreement with those of Mucheru-Muna et al. [18] who reported that Leucaena gave the highest benefit to cost ratio while manure and Tithonia with half recommended rate of inorganic fertilizer gave the lowest. Though Mutuo et al. [35] indicated that organics have high labor costs, the results on both soils indicated that treatments that received sole organics and those combining organic and mineral fertilizers (except Calliandra with half recommended rate of mineral fertilizer) recorded a return to labor greaterthan 2.0, the minimum acceptable for small holder farming activities. Some of the organic materials like Calliandra and Leucaena could be more economically attractive when used as animal feed protein supplement for dairy cattle [5] and the manure returned to the farm. Maximum maize yield, net benefit and return to labor and benefit to cost ratio obtained on ustic Oxisol compared to umbric Cambisol could be attributed to the soil texture. The differences observed in maize yield, net benefit and return to labor and benefit to cost ratio on umbric Cambisol and ustic Oxisol could be attributed to the type of soil, the sandy soil favored more the N mineralization and take up processes than the clayey loam or soil nutrient status [18] [36].