Abstract:

Nitrogen fertilizer application plays an important role in world food production and in ensuring food security in China. To elucidate the effects of different ammonium nitrogen fertilizer application rates on nitrogen leaching and surface electrochemical properties of various types of purple soil， a pot experiment was conducted. Three different types of purple soil were selected， and four treatments were set up： no nitrogen fertilizer （CK）， low nitrogen （N₁， 0.1 g elemental nitrogen per kg soil）， medium nitrogen （N₂， 0.2 g elemental nitrogen per kg soil）， and high nitrogen （N₃， 0.4 g elemental nitrogen per kg soil）. The results showed that with increasing nitrogen fertilizer application rates， compared with the control group （CK）， the pH values of red brown purple soil， gray brown purple soil， and brown purple soil under the N₃ treatment decreased by 0.9， 1.2， and 0.8， respectively. Meanwhile， the cumulative leaching losses of ammonium nitrogen and nitrate nitrogen in these three types of soil increased significantly （P<0.05）. The ammonium nitrogen leaching losses under the N₃ treatment increased by 7.1， 15.4， and 12.5 times compared with those under the control （CK） treatment， respectively. There was almost no nitrate nitrogen leaching loss in the CK treatment. The nitrate nitrogen leaching losses under the N3 treatment increased by 6.1， 4.9， and 1.8 times compared with those under the N₁ treatment， respectively（P<0.05）. The surface potential （φ₀）， surface electric field strength （E₀）， and surface charge density （σ₀） of the three types of purple soil showed similar increasing trends， while the specific surface area （S） and surface charge number （SCN） decreased. Under the same nitrogen fertilizer application rates， there were differences in nitrogen leaching and surface electrochemical properties among the different types of purple soil. In the N₃ treatment， the cumulative leaching of ammonium nitrogen in gray-brown purple soil was significantly higher than that in the other two types of purple soil. Additionally， under all nitrogen fertilizer treatments， the cumulative total amount of nitrate nitrogen leached in gray-brown purple soil was significantly higher than that in red-brown purple soil （P<0.05）. Under the N₁ treatment， φ₀ of gray-brown purple soil was higher， while under the N₃ treatment， φ₀ of brown purple soil was significantly higher than that of the other two soil types. Under all treatments， the E₀ of gray-brown purple soil was significantly higher than that of the other two soil types （P<0.05）. Furthermore， under the N₂ and N₃ treatments， the σ₀ of gray-brown purple soil was also significantly higher than that of the other two soil types （P<0.05）. S under the N₁， N₂， and N₃ treatments ranked： red-brown purple soil>brown purple soil>gray-brown purple soil. Under the N₃ treatment， SCN of red-brown purple soil was significantly higher than that of the other two soil types （P<0.05）. Therefore， excessive application of ammonium nitrogen fertilizer can lead to soil acidification in purple soils， significantly altering their surface electrochemical properties and reducing their ability to adsorb and retain nutrients.

Key words: ammonium nitrogen fertilizer, purple soil, nitrogen leaching, surface electrochemical properties of soil