Abstract:

Latosolic red soil is the predominant soil type in Guangdong province. In this study， we explored the current status of， and changes in， the soil fertility of vegetable fields located in the latosolic red soil zone. The ultimate aim was to provide a scientific basis for evaluating the management of cultivation and fertilization during vegetable production， with a goal to protect and improve farmland. We selected 89 perennial vegetable fields， i.e.， fields cultivated with various vegetables annually， in the cities of Guangzhou， Jiangmen， and Zhaoqing， and the district of Huiyang of Huizhou city in the Pearl River Delta in Guangdong province， and collected surface soil samples for analyses of soil physicochemical parameters. The results were compared with the National Nutrient Classification Standard of The Second Soil Census and the Nemero index. It was found that loam soil， sandy loam soil， and silty loam soil were the dominant categories of soil texture， accounting for 46.1%， 23.6%， and 19.1%， respectively， of all the soil samples from perennial vegetable fields. The soil was characterized as slightly acidic （average pH， 5.83）， the organic matter content was classified as medium （average， 23.83 g·kg^-1）， and the cation exchange capacity was classified as medium-low ［average， 8.67 cmol（+）·kg^–1］. The concentrations of soil total nitrogen （N）， total phosphorus （P）， and total potassium （K） were 1.19 g·kg^-1， 1.47 g·kg^-1， and 12.53 g·kg^-1， respectively， corresponding to medium （total N， total P） and medium-low （total K） levels. The soil was rich in available N and available P （135.24 mg·kg^-1 and 120.24 mg·kg^-1， respectively） and extremely rich in available K （222.48 mg·kg^-1）. The Nemero index was 1.69， indicative of fine status of soil fertility. Compared with the data obtained for latosolic red soil in Guangdong province in The National Second Soil Census， the soil total K concentration had decreased， whereas the soil pH， organic matter content， total N， and available N had increased by 16.6%， 23.5%， 38.4%， and 62.5%， respectively， and the soil cation exchange capacity and total P， available P， and available K contents had markedly increased by 1.29-， 6.00-， 65.80-， and 3.07-times， respectively. Soil available P had accumulated substantially in most of the sampled vegetable fields. The annual accumulation rates of soil total N and total P were 8.46 mg·kg^-1 and 32.31 mg·kg^-1， respectively， and those of soil available N， available P， and available K were 1.20 mg·kg^-1， 3.04 mg·kg^-1， and 4.30 mg·kg^-1， respectively. In general， soil fertility in vegetable fields of the Pearl River Delta in the latosolic red soil zone has improved under local tillage management over the last 40 years. The soil has shifted from acid to slightly acid， the cation exchange capacity and organic matter and total N contents have improved by one grade， the available N and available K contents have improved by two grades， and the soil total P and available P have improved by three and five grades， respectively. Thus， soil fertility in the research area has improved from inferior status （i.e. extremely insufficient to medium-low level） in 1980 to the current preferable status （medium-low level to extremely rich）. To improve the fertility of vegetable fields and maintain the sustainable utilization of soil resources in the latosolic red soil zone of the Pearl River Delta， the combined application of organic manure and chemical fertilizers is recommended during local vegetable production. It will be important to use optimum inputs of N and K fertilizers and reduce inputs of P fertilizer.

Key words: latosolic red soil, soil fertility, perennial vegetable fields, cation exchange capacity, cropland quality