دانلود رایگان مقاله نرخ اسیدی شدن خاک در مزارع چای و علل احتمالی

ABSTRACT

Soil acidification has threatened the sustainability of agricultural systems. Organic manures have been reported to alleviate soil acidification in tea (Camellia sinensis) plantations. However, little is known about the pH status at different soil depths in these plantations. Whether the downward movement of acid contributes to subsurface soil acidification and the magnitude of the movement are unknown. We took soil samples from tea plantations that were 5,10, 20, 33, and 56 years old at depths up to 120 cm in the soil profile. We examined the soil pH, Fe, Al, nitrate N (NO3-N), ammonium N (NH4-N), and organic carbon (OC) in every 20-cm soil layer, and observed the downward movement of H+ , NH4-N, and OC using undisturbed soil column experiments. The results show that organic manures and plant residues increased the topsoil pH, but did not reduce soil acidification below 80 cm. At a planting density of 10,000 plants ha
1 and with the application of organic manures at 6000 kg ha
1 a
1 , the soil acidification rates (decrease in pH) were
0.0161 and
0.0245 per year at depths of 80–100 and 100–120 cm, respectively. The soil pH increased by 0.0158 and 0.0140 per year at depths of 0–20 and 20–40 cm, respectively. The downward movement of acid is one cause of topsoil alkalization and deeper soil acidification in cultivated tea plantations. No-till farming and increased vegetation coverage to reduce the downward movement of H+ , NH4-N, and OC are effective measures to alleviate deep-soil acidification. Planting density also affects soil acidification; tea trees excrete less H+ into the rhizosphere at a lower planting density than at a higher planting density. Tea plantation soil is not acidified at a lower planting density of 5000 plants ha
1 .

5. Conclusions

Our investigation of the soil pH at plantations with different tea cultivation periods and in the 0–120-cm layer led to the following conclusions. Except for the 56-year-old tea plantations, there were significant positive linear correlations between tea cultivation age and soil pH in the 0–20-cm and 20–40-cm layers, with alkalization rates (increase in pH) of 0.0158 and 0.0140 per year, respectively. The soil pH in the 40–80-cm layer did not change significantly. There was a significant negative linear correlation in the 80–100- cm and 100–120-cm layers, with acidification rates of
0.0161 and
0.0245 per year, respectively. Planting density is an important factor in affecting soil acidification, and reduces the planting density can reduce the production of H+ so that it reduces soil acidification. The tea plantation soils exhibited no acidification at a lower planting density of 5000 plants ha
1 . Organic manure cannot alleviate deep-soil acidification in acid soil tea plantations. Our results demonstrate that the downward movement of acid is one cause of topsoil alkalization and deeper soil acidification in cultivated tea plantations. No-till farming is an effective measure to alleviate deep soil acidification.