Abstract

An in situ nitrogen mineralization experiment was conducted to assess the response of chicken and cow manure application at two different rates (5 and 10 Mg DM ha^-1) on net N mineralization in a maize-bean rotation experiment in Nicaragua. The field study was carried out over four consecutive growing seasons. Soil samples of the top soil (0 - 0.3 m) were taken every 30 days within the season in inserted plastic tubes. The samples were analysed for content of soil mineral N and total organic N. Net N mineralization was estimated as the difference in soil mineral N over time. The net N mineralization rate in the treatment with chicken manure applied at the high rate (CHH) was on average 24.5 g N m^-2 season^-1 and significantly higher than all the other treatments and the unfertilized control, except during the first season. From season two to season four, the net N mineralization of cow manure at both high and low application rates were similar to that of low application rate of chicken manure.  In the control, the net N mineralization was significantly lower than in all fertilisation treatments and on average 9.9 g N m^-2season^-1. It also decreased significantly over time and did not show any indication to increase in the season following the N₂ fixating crop. Only the CHH treatment showed such a tendency. The soil total organic N did not show any clear pattern over neither time nor treatment. Consequently, the variation in specific net N mineralization per unit of total organic soil N was similar to that of net N mineralization and ranged from 1.6 – 2.9 10^-3 30d^-1 in the control to 4.4 - 6.7 10^-330 d^-1 in CHH.

Key words: Soil organic matter, low input tropical agriculture, Zea mays L.,Phaseolus vulgaris L.