ABSTRACT

Crop responses to nitrogen (N) fertilization reportedly depend on the storage of soluble N in the soil profile from the previous N-fertilization. We examined the profile storage of dissolved inorganic, DIN (NH₄-N + NO₃-N), and dissolved organic N, DON, in a savanna soil fertilized for over 50 years with farmyard manure, FYM, NPK-fertilizer, and their combination, FYM+NPK, along with a control plot and a native site, to determine the fertilization practice that best conserved soluble N from previous N-fertilization for subsequent cropping. The weight of total dissolved N (TDN) of 196 kg ha⁻¹ in the soil profile under native vegetation was 3–4 times greater than 53 kg ha⁻¹ in FYM+NPK-plot and the 64 and 65 kg ha⁻¹ in the FYM-only and NPK-only, respectively. The NO₃-N weight of 93 kg ha⁻¹ under native vegetation was 5–9 times greater than the 11 kg ha⁻¹ (NPK-only) to 19 kg ha⁻¹ in the control. The DON weight of 45 kg ha⁻¹ (native site) was 2–15 times greater than the 3 kg ha⁻¹ in FYM+ NPK-plot and 29 kg ha⁻¹ in NPK-only. Compartmentalizing the profile into the root zone (0–60 cm) and beyond the root zone (60–120 cm) indicated 76% NO₃-N and 38% DON storage beyond the root zone under native vegetation due to leaching. Mean percentage changes in TDN in soil profiles under cultivation, using the native site as the reference, were – 83% for NO₃-N, – 73% for DON, and – 29% for NH₄-N, but the changes varied with fertilization practices.

摘要

据报道，作物对氮 (N) 施肥的反应取决于先前施氮的土壤剖面中可溶性氮的储存量。我们检查了在使用农家肥、FYM、NPK 肥料及其施肥 50 多年的稀树草原土壤中溶解无机氮(NH ₄ -N + NO ₃ -N) 和溶解有机氮 DON的剖面储存情况。结合 FYM+NPK 以及对照地块和原生地点，以确定最能保留先前施氮中可溶性氮以用于后续作物的施肥实践。天然植被下土壤剖面中 196 kg ha ^-1的总溶解氮 (TDN) 的重量是FYM+NPK 样地中53 kg ha ^-1和 64 和 65 kg ha ^{-1 的}3-4 倍分别在 FYM-only 和 NPK-only 中。天然植被下93 kg ha ^-1的 NO ₃ -N 重量是对照中11 kg ha ^-1（仅 NPK）至 19 kg ha ^{-1 的}5-9 倍。45 kg ha ^-1（原生地点）的 DON 重量是FYM+ NPK 地块中的 3 kg ha ^-1和仅 NPK 中的29 kg ha ^{-1 的}2-15 倍。将剖面划分为根区（0-60 厘米）和根区以外（60-120 厘米）表明，由于浸出，原生植被下根区以外有76% 的 NO ₃ -N 和 38% 的 DON 储存。使用原生地点作为参考，栽培土壤剖面中 TDN 的平均百分比变化为 – 83% 的 NO₃ -N，DON 为 – 73%，NH ₄ -N为 – 29% ，但变化因施肥实践而异。