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Effects of biochar on crop and soil under field conditions have been lacking. Thus, a field experiment was conducted on an Oxisol (Rhodic haplustox, Wahiawa series) in Oahu Island, Hawaii. A biochar locally produced from macadamia shell feedstock was applied along with either urea, or organic nitrogen (N) fertilizers (blood meal: 10% N and Organic Farm: 12% N). Sweet corn (Zea mays), soybean (Glycine max), and okra (Abelmoschus esculentus) served as the test crops. The N application rates were 150 and 300 kg N/ha, and biochar rates were 0, 2, and 4% by weight. The experiment had a factorial design, with biochar rate as main plot, N source as subplot, and N rate as sub-subplot. There were 3 replications per treatment. Table 1 shows selected chemical properties of the soil and biochar; and Figure 1 shows the set-up of the experiment (see the attached).
Our preliminary results showed that the N use efficiency markedly increased in the presence of biochar, especially for corn, okra, and even soybean (Tables 2 and 3, see the PDF file attached). Interestingly, the effect of biochar on plant growth seemed to extend beyond N nutrition because the treatments receiving biochar but no N input also out-yielded those having N input but no biochar (Figure 2,see the PDF file attached). Our experiment will be continued for some more years to test the prolonged/aging effect of biochar.
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