Effects of nitrogenous fertilizers on the chemical properties of polluted paddy soil and the accumulation of Cd in mulberry

Nitrogenous fertilizer (N fertilizer) is crucial to the quality of mulberry leaves. This study evaluated the influences of 4 N fertilizers on the chemical properties of paddy soil, mulberry growth, leaf quality and Cd distribution in mulberry. The results showed the soil pH was reduced with the increasing concentrations of NH₄Cl and (NH₄)₂SO₄. The soil pH for NH₄Cl and (NH₄)₂SO₄ treatments were 4.60 and 4.62 at 300 mg N/kg soil, 21.10% and 20.75% lower than that of the control, respectively. CO(NH₂)₂ increased soil organic matter (OM) and the 4 N fertilizers all increased the Cd phytoavailability with (NH₄)₂SO₄>NH₄Cl > CO(NH₂)₂>NaNO₃. (NH₄)₂SO₄ and CO(NH₂)₂ improved leaf production, total mulberry biomass and the total sugar in leaf. CO(NH₂)₂, NH₄Cl and NaNO₃ increased the crude protein content and (NH₄)₂SO₄ increased the chlorophyll content (8.10%∼20.20%). (NH₄)₂SO₄ and NH₄Cl increased the Cd concentration in leaf, stem and root. CO(NH₂)₂ increased Cd concentration in leaf and stem. All 4 N fertilizers decreased the percentage content of Cd in roots (1.80%∼37.74%) and increased it in stems (3.90%∼263.81%) and leaves (24.09%∼236.18%). The leaves from the CO(NH₂)₂ and NaNO₃ treatments met the hygienical standard for feeds. CO(NH₂)₂ and NaNO₃ could be recommended to safely utilize the Cd polluted acidic paddy soils.