Nitrogen biovailability in Mauritian soils under sugarcane cultivation amended with agricultural composts

Abstract

Nitrogen (N) plays a vital role in plant metabolic processes, and may cause severe economic losses in crop production if deficient. When agricultural composts are used to counteract soil impoverishment and supply crop nutrients, it is crucial to understand the dynamics of nitrogenous compounds to optimize N uptake. Five major soil groups of Mauritius were amended with three types of compost, filtercake (FC), poultry litter (PL), and poultry manure-sugarcane thrash (PM), at application rates to supply 140 kg N ha-1in a laboratory incubation experiment over 215 days. In each soil group, only specific types of agricultural composts resulted in a statistically significant (P < 0.05) increase in cumulative N mineralized, relative to the control: PM in the Low Humic Latosol (L), PM and PL in the Humic Latosol (H), PL in the Humic Ferruginous Latosol (F), PL in the Latosolic Reddish Prairie (P) group, and FC and PL in the Latosolic Brown Forest (B) group. In general, the N-NO3- form was dominant in all the treatments across the soil groups. Only in the H soil amended with PM and PL was the N-NH4+ form pre-dominant. The index of N availability, N0k, showed that in control soils, the daily N availability (mg N kg-1 soil day-1) was in the order B (1.242) > H (0.975) > F (0.674) > P (0.637) > L (0.524). The relatively high N availability in the B may explain why sugarcane cultivated in this soil islowly responsive to increments in N fertilizers. Relative to the control soils, FC resulted in a decrease in N availability, mostly due to a relatively slower rate of N mineralization. Poultry litter compost increased daily N availability in all the soil groups. Increased N availability was also noted in all soils amended with PM, except in the P soil. In general, the percentage of organic N mineralization in control soils varied from 2% to 4%. In FC-amended soils, between 2% and 5% of the organic N from soil and compost mineralized. Applied in the weathered soil groups (H, L and F), PM resulted in an appreciable increase in organic N mineralized that varied between 6% and 9%. However, in the immature soil, PM had a relatively mitigated effect, with 1% of total N mineralization in the amended P soil, and 3% in the B soil. Across the soil groups amended with PL, from 4% to 8% of the total soil and compost organic N mineralized.