Influence of Biochar and Animal Manures Application on Ammonia and Nitrate Concentrations in the Root and Shoot of Three Varieties of Turnips

Abstract

Many investigators have focused on the impact of fertilizers on crop yield and ignored fertilizers impact on the plants composition. The impact of seven types of soil treatments (sewage sludge, horse manure, chicken manure, vermicompost, elemental organic fertilizer, inorganic fertilizer, and native soil) and similar seven treatments amended with biochar on the concentrations of NH3 and NO3 in the roots and shoots of three commercial varieties of turnips, Brassica rapa was investigated. The three varieties (Purple Top White Globe PTWG, Scarlet Queen Red SQR, and Tokyo Cross TC) varied in concentrations of NH3 and NO3 levels. High levels of NO3 in edible plants is associated with harmful effects on human health, due to the risk of creation of carcinogenic N-nitroso compounds. NO3 in SQR roots and shoots (edible greens) was greater than varieties PTWG and TC. The concentration of NH3 averaged 20.2, 12.8, and 8.9 µg g−1 fresh turnip roots, whereas NO3 values averaged 107.6, 64.1, and 62.9 µg g−1 fresh turnip roots in varieties SQR, PTWG, and TC, respectively. Regardless of soil amendment type, the concentration of NH3 in the shoots (44.0 µg g−1) was greater than the roots (15 µg g−1). On the contrary, NO3 was higher in the roots (89.4 µg g−1) compared to the shoots (67.6 µg g−1 fresh tissue). Overall, biochar added to vermicompost amended soil increased NH3 by 73% compared to vermicompost not amended with biochar. Regarding acceptable daily intake (ADI) for NO3, none of the three varieties analyzed constitute any NO3 adverse effects on normal human intake. Similarly, consuming turnips grown in any of the animal manures tested do not represent any hazardous issues.