Effects of application rates of carbonized cattle manure and subsequent salt removal on the growth and nutrient uptake of Komatsuna (Brassica rapa L.) and nutrient leaching from the soil

Carbonized cattle manure (CCU) are a promising alternative for recycling animal waste on farm lands while minimizing nitrogen loads to the environment. The objectives of this study were to examine the effects of CCU application rate and subsequent salt removal by irrigation on the growth and nutrient uptake of Komatsuna (Brassica rapa L.), and nutrient leaching from the soil. The CCU produced at 500 deg C was applied to two different soils, a humic Andosol and a coarser-textured Brown Lowland soil, in an amount equivalent to 1, 3 or 6 times the recommended phosphate fertilizer application of 150 kg-P2O5/ha. Where CCU equivalent to 900 kg-P2O5/ha was applied, salt removal treatment was also tested by applying 63 mm of irrigation water 7 and 48 d after seeding. Irrespective of the CCU application rate, no plant growth inhibition was observed in the Andosol, while the growth was significantly inhibited in the Brown Lowland soil when CCU equivalent to 450 kg-P2O5/ha or more was applied. After the first salt removal by irrigation, the growth inhibition became statistically insignificant in terms of dry weight of the upper plant, although a suppression of P, K, Ca and Mg uptake was still observed. The dominant leached ions upon the first salt removal treatment were Cl and K, with the concentrations in the effluent of 3,774 mg/L and 2,069 mg/L, respectively, from the Brown Lowland soil, and 2,025 mg/L and 2,517 mg/L, respectively, from the Andosol. These highly concentrated salts were assumed to be derived from the CCU and responsible for the inhibition of the plant growth. The double salt removal treatments were ineffective in view of the fact that the leached Cl accounted for only 13% of Cl contained in the CCU applied to the pot. These results suggest that the CCU should be applied at a rate equivalent to the recommended P fertilizer application, and that salt removal from the CCU prior to application should be effective for avoiding salt problems.