Chicken manure composts as nitrogen sources and their effect on the growth and quality of Komatsuna (Brassica rapa L.)

Environmental issues on the excessive use of chemical fertilizer and energy shortage in recent years have led to the renewed interest in using organic materials. The return of animal manure into crop fields is considered to be one of the most effective methods in reducing the use of industrially produced chemical fertilizer as well as utilizing the mineral nutrients in crop production waste. The use of animal manure as fertilizer, due to the availability of the nutrients contained in organic materials, has been of concern to agronomists and promoted in recent years in an attempt to increase the amount of soil organic matter and eventually to improve land productivity. The study was conducted in two consecutive experiments to observe the effect of five chicken-manure composts with different nitrogen content and to investigate their residual effect on crop yield and its quality. Chicken-manure composts (Ch-1 to Ch-5) were applied to 2 kg soil of Andisol in pot experiments and Komatsuna (Brassica rapa L.) vegetable was used as a sink of mineralized-N from chicken-manure composts. Unmanured pot was used as control, whereas pot fertilized with urea was used as standard of comparison for chemical fertilizer. Potassium chloride (KCl) and triple super phosphate (TSP) were added again at the same rate to the urea pot (U-1). However, compost was not applied in the second batch of chicken-manure compost treatments. The addition of chicken-manure composts resulted in significant differences in yield compared with control, but Ch-3 and Ch-5 did not have significant differences with urea. The residual effect of the chicken manures still resulted in increased Komatsuna yield for Ch-3 and Ch-5, and it enhanced yield significantly compared to residual urea (U-1); whereas the other treatments exhibited lower yield than those in the first batch of experiment. The increase in Komatsuna yield of Ch-3 and Ch-5 treatment in the second batch of the experiment might be caused by the higher N mineralization rate where in residual inorganic N remained in the soil after the first batch of the experiment. Nitrate accumulation in plant was induced by increased N mineralization in soils. The application of Ch-3 and Ch-5 and urea increased greatly nitrate accumulation in Komatsuna plant, while Ch-1, which had slower N mineralization, induced smaller nitrate accumulation. The content of glucose and reducing sugar tended to be lower with the increase of the nitrate content of Komatsuna.