Demand-Driven Technologies for Sustainable Maize ... - IITA

149Table 8. Rotation† and fertilizer effects on cation exchange capacity of0-15 cm of a Typic Haplustalf.RotationMS1 MS2 MF MM MeanFertilizer (kg N ha -1 ) ----- Cation exchange capacity, cmol ckg -1 ------0 2.09 2.52 2.07 1.79 2.1290 3.76 4.30 2.83 2.66 3.39Mean 2.93 3.41 2.45 2.23LSD (0.01)Rotation (R) 0.49Fertilizer (F) 0.39R x F 0.77† MS1 = TGx 1448-2E-Maize; MS2 = Samsoy-2-Maize; MF = Fallow-Maize;MM = Continuous maizehigh capacity to extract non-exchangeable K thus indicating that itrecycles soil K effectively. The exchangeable K level in the unfertilizedMM plot dropped below the initial soil K, whereas it was maintainedat a relatively high level in the fertilized plot.Exchangeable acidity was not affected either by rotation, fertilizationor their interaction (Table 8). The mean values were 0.117, 0.110,0.090 and 0.057 cmol ckg -1 for MS1, MS2, MF, and MM, respectively.In terms of fertilization, mean values were 0.080 and 0.102 cmol ckg -1for 0 and 90 kg N ha -1 , respectively. Trend in exchangeable acidity wassimilar to that of exchangeable K. Soil OC or soil organic matter (SOM)plays a dominant role in the cation exchange capacity (CEC) of thissoil, which is dominated by kaolinite. Jones and Wild (1975) indicatedthat over 80% of CEC of savanna soils is contributed by SOM. Whencombined with other measures of soil fertility, CEC is a good indicatorof soil quality and productivity. A comparison of change in CEC valuesand exchangeable bases of various treatments is shown in Table 7.There were signifi cant effects of rotation on CEC and exchangeablebases (Ca, Mg, and K) and rotation x fertilizer interaction. Generally,MS2 treatment gave the highest effective CEC (sum of cations) andthe lowest was observed on MM treatments.Low pH in unfertilized continuous maize may be responsible for thelow CEC value. A non-N benefi t of soybean rotation was evident fromthe CEC values obtained. The CEC value obtained from unfertilizedMS2 plot was similar to the value obtained in fertilized MM. Thisconfi rms that the increased maize yield normally reported in soybeanmaizerotation system is not solely infl uenced by N supply but dueto other rotation effects. These effects also include reduced diseaseincidence and addition of growth promoting substances in addition toimprovement in soil physical and chemical properties. Fertilized maizeplots in all the rotations resulted in a signifi cant increase in CEC andexchangeable bases compared to the unfertilized plots.