MINERALIZATION OF NEEM SEED CAKE AND EFFECT ON GROWTH AND NUTRITION OF SORGHUM IN A NORTHERN GUINEA SAVANNA ALFISOL

MINERALIZATION OF NEEM SEED CAKE AND EFFECT ON GROWTH AND NUTRITION OF SORGHUM IN A NORTHERN GUINEA SAVANNA ALFISOL

Abstract:

Four neem seed cake levels 0, 1, 2 and 4 ton (t) ha-1 along with varying rates of inorganic fertilizer recommendation (0, ¼, ½ and full) for sorghum were evaluated in the laboratory, greenhouse and in the field for their mineralization and/or decomposition potentials, impact on soil fertility, productivity and nutrition of sorghum in the Northern Guinea Savanna of Nigeria in a factorial completely randomized design with three replications. Results showed that NSC contained 265.35 g kg-1 OC, 45.95 g kg-1 N, 2.75 g kg-1 P, and 12.35 g kg-1 K mean concentration in both years indicating its potential in improving soil fertility and plant growth. Treatments did not significantly (P ≤ 0.05) increase sorghum growth and dry matter yield (DMY) in the greenhouse. The quarter recommended rate (RR) recorded a higher increase in DMY and plant height while combinations of 2 t ha-1 NSC + ¼ RR and 4 t ha-1 + FRR gave non-significant increase in stem girth and number of leaves respectively. Treatments showed significant (P ≤ 0.05) difference in only P concentrations in sorghum tissue. The 4 t ha-1 of NSC significantly increased P and K concentrations while combined application of 4t ha-1 + FRR recorded the highest N concentration. As regards the effects of treatments on soil properties after cropping, sole NSC and CF treatments resulted in soil pH reduction, implying that application of these materials can lead to soil acidification. Significant (P ≤ 0.05) increases were observed in the effect of treatments on exchangeable acidity, nitrogen, potassium and calcium. Soil microbial biomass carbon correlated with soil total organic carbon (TOC) (r = 1), and was generally positively related to the soil organic matter which implied the ability of the organic material to form stable aggregates. Laboratory incubation study showed an initial rapid cumulative N mineralization rate in the first twenty-one (21) days followed by slower release with time. At 98 days, cumulative N mineralization represented 50 % of total N applied as neem seed cake. N mineralization pattern showed that ammonium-N fraction in the soil far exceeded nitrate-N fraction, accounting for 91.5% of the N mineralized from the NSC. The simple rate constant (h=k) gave a better fit to mineral-N released than the Gompertz function in the laboratory study. However, in the field, cumulative N mineralization with time showed an initial rapid rate in the first six (6) weeks after incubation followed by slower release in 2009 and 2010. N mineralization pattern showed that ammonium-N fraction in the soil slightly exceeded the nitrate-N fraction in 2009, accounting for about 52% of N mineralized from neem seed cake while in 2010 N mineralization pattern showed that nitrate-N fraction in the soil far exceeded the ammonium-N fraction, accounting for 64% of the N mineralized from NSC. Generally, highest concentration of ammonium was observed during the first twenty-eight (28) days of incubation. The best fit for net N mineralization in the field was displayed with the Gompertz function. Weight loss of NSC was rapid within the first twenty-eight (28) days with about 70% lost in 2009. Significant (P < 0.05) decrease in dry mass was observed for seven sampling periods in 2010; dry mass loss was rapid during the first fourteen (14) days of decomposition relative to later periods. However, NPK level did not affect dry mass loss of NSC significantly (P < 0.05). Decomposition best fit was described by the asymptotic negative exponential model. In the field trial, significant treatment effects were observed on sorghum growth parameters. Leaf number, dry matter yield and plant height increased with simple combined application of the amendments. Effects of the various treatments (regression) on yield was significant, a reflection of the contribution of treatments to soil nutrient status. Combined application of 1 t ha- 1 + FRR had highest sorghum grain yield. Yield parameters were better enhanced in NSC amended plots in 2009 and 2010 (P < 0.01). There was no significant effect of treatments on P and K concentrations in sorghum tissues in 2009. The effect of treatments on soil properties after cropping, sole CF and NSC treatments resulted in soil pH reduction, implying increase in acidity. Significant (P ≤ 0.05) increases were observed in the effect of treatments on organic carbon and exchangeable potassium in 2009 and 2010 with sole NSC application while in 2010 significant effect was observed for exchangeable potassium, calcium and exchangeable acidity in sole NPK plots. Non significant treatment effect was observed for tannin content in both years while significant (P ≤ 0.05) response was obtained for effect of chemical fertilizer in 2009 for crude protein. The present study revealed that NSC has high residue quality and can be used as a nutrient source. Its integration with CF was shown to be an important management strategy for improving fertility and productivity of the savanna soils

MINERALIZATION OF NEEM SEED CAKE AND EFFECT ON GROWTH AND NUTRITION OF SORGHUM IN A NORTHERN GUINEA SAVANNA ALFISOL

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