Abstract
Organo-mineral nutrient sources are promising soil amendments for sustainable crop production in Nigeria. A field experiment was conducted at the Teaching and Research Farm of the Cross River University of Technology Obubra during the 2016 cropping season. The objective of the study was to evaluate the effects of nitrogen (N) and amended rice mill waste (RMW) on some soil chemical properties and yield of maize (Zea mays L.). The treatments consisted of 10 kg ha-1 RMW as control and 10 kg ha-1 of RMW amended with 10, 20, 30, 40 or 50 kg N ha-1. The 6 treatments were replicated 3 times under RCBD with each experimental plot size measuring 4 × 3 m. All the treatments including control increased the chemical properties of the soil over the initial soil properties including total N, available P, SOM, pH and the exch. Cations; Ca2+, K+, Mg2+, Na+. RMW + 40 kg N ha-1 and RMW 50 kg N ha-1 produced tallest plants, highest number of leaves per plant and largest leaf area of maize plants. RMW + 30 kg N ha-1, RMW + 40 kg N ha-1 and RMW + 50 kg N ha-1 produced the highest number of seeds per cob, highest plant dry matter and highest grain yield per unit area of 2.61 and 2.59 t ha-1 respectively in 2016 and 2.63 and 2.62 t ha-1 grain yield in 2017 while the least grain yield was obtained from the control (0.81 and 0.83 t ha-1 respectively for 2016 and 2017). Rice mill waste amended with 30 kg N ha-1 is therefore recommended for optimum economic yield of maize in Obubra Rainforest soil and the improvement of soil chemical properties for sustainability. Key words: Fortified, rice mill waste, organo-mineral, N-fertilizer, maize, rainforest  
Highlights
Recycling of agricultural waste is a great resource for sustainable crop yields in Nigeria
Soils in the humid tropics are poor in organic matter and available nutrients; their productivity and sustainability decline over time when subjected to continuous cultivation (Zingore et al, 2003)
The maintenance of soil organic matter is the basis of sustainable crop production in Nigeria and the tropics in general (Oladipo et al, 2005)
Summary
Recycling of agricultural waste is a great resource for sustainable crop yields in Nigeria. The maintenance of soil organic matter is the basis of sustainable crop production in Nigeria and the tropics in general (Oladipo et al, 2005). Organic manures are bulky and low in nutrient contents, Chiroma et al (2006) noted that they are capable of valuable contribution to continuous demand of crop nutrients. They contribute in conditioning the soil physically for improved crop environment such as structure of soil, reduced bulk density, increased porosity and water and nutrient retention. Rice mill waste (husk) abounds in rice growing and processing areas in bulk with low nitrogen contents which can be recycled for soil
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