Effects of long-term fertilization on As (arsenate) accumulation intypical fluvo-aquic soils and crops

Huang-Huai-Hai Plain is a strategic grain production base in China with a wild distribution of fertile fluvo-aquic soils. During the past 20 years, high-input intensive agriculture with excess chemical fertilizer application has sustained high grain yields. However, unreasonable field management has resulted in potential pollution issues in the plain. In this study, the effects of long-term differential fertilization practices on the accumulation of arsenate (As) in typical fluvo-aquic soils and crops were investigated. Field experiments were launched in 1989, in which 7 treatments were established. The treatments included OM (organic manure), OM+NPK (50% organic manure + 50% chemical fertilizer), NPK, NP, PK, NK and CK (the control experiment with no fertilizer). With over 20 years (1989-2009) of cultivation, As in the surface (0~20 cm) and subsurface (20~40 cm) soil layers markedly accumulated. The soil As content was, however, too low for loading negative effects on eco-agricultural safety. As accumulation in the plain was mainly affected by irrigation and deposition, and relatively less affected by different fertilizer applications. The content of As in phosphorus (P) fertilizers was higher than in nitrogen (N) and potassium (K) fertilizers or in organic manure (OM). Hence P fertilization was the main drive of soil As accumulation in the plain. Nevertheless, long-term P fertilization did not significantly increase soil As content since it was largely used up by crops. Also As accumulation trend slowed with OM fertilization. Crop tissue content of As was in the order of root > stalk > grain. Grain As content was not only significantly lower than that of root or stalk, but also than that of China's national standard. For different fertilization treatments, wheat tissue As content was in the order of PK > OM > OM+NPK > NPK > NP > NK > CK. This was somehow similar to that of soil available P, which was indirectly affected by soil organic matter content. Under OM, OM+NPK, NPK and NP treatments, there was high soil organic matter accumulation, which led to high crop yields. Although soil organic matter promoted high As adsorption by wheat, it had no significant effect on maize root As content. Since maize cultivation period was relatively short, low soil available As content inhabited maize root As content. More As was adsorbed by maize stalk due to strengthened transferability.