Fertilizer Effect on Carbon Dynamics of Different Texture Soils under Tomato Cultures

Abstract

The risk of nitrate (NO3) leaching is enhanced under tomato culture because of the high water demand, especially in fertilized coarse‐texture soils. To avoid this, slow‐release fertilizers or manure use is recommended. We studied the effect of a slow release and a common fertilizer on the carbon (C) and nitrogen (N) dynamics of drip‐irrigated tomato culture at a macro‐pot (lysimeter) field trial in three different texture soils. The treatments included an initial blanket application of slow‐release fertilizer to all the pots 1 week after planting, followed by supplemental application of N 3 or 6 weeks later. The C and N contents of the microbial biomass differed among the soils. They were significantly less in sandy soil than in the other loam texture soils. A close relation (r2 = 0.85) was found between microbial C and N. Their mean ratio was 6.7, being lowest in the sandy (6.0), and the highest in the clay loam (7.0) soil, but without significant difference. The rate of cellulose decomposition tended to decrease in the sandy soil in each of the three observed periods. The two highest N addition treatments (120 and 180 kg.ha−1 N) accelerated cellulose decay compared with the control and low N addition (60 kg.ha−1 N), especially in the clay loam soil. Nitrate adsorbed by ion‐exchange resin bags in the 0‐ to 30‐cm soil depth did not differ significantly between treatments, and there was no enhancement in nitrate leaching due to repeated fertilizer application.