Effect of nitrogen and phosphorus application on agricultural soil food webs

Aim of the present research is to investigate the effect of nitrogen (N) and phosphorus (P) on soil food webs (microbes, nematodes and microarthropods) trophic interactions in agriculture ecosystems. A complete randomized block design experiment of N and P fertilization was initiated in 2010 with four treatments: (1) P-addition, (2) N-addition, (3) NP-addition and (4) control. After 4years of fertilization, compared with control, N-addition had a negative effect on microarthropods and clarify indirectly by significantly (P<0.05) increasing soil total nitrogen (0.37g kg(-1)) and available nitrogen (20.03mg kg(-1)). The reduction in microarthropods resulted significant (P<0.05) increase in bacterivores and fungivores feeding on bacteria and fungi, an example of top-down control. P-addition had indirect negative effects on microarthropods by means of significantly (P<0.05) increasing soil total phosphorus (0.62g kg(-1)) and available phosphorus (24.17mg kg(-1)), aggravated fungivores feeding on fungi and strengthened top-down control. NP-addition significantly (P<0.05) increased total microbial biomass, nematodes and microarthropods and resulted in bottom-up control. These results suggested that top-down effects were the dominant force in N- or P-addition treatments. NP-addition strengthened bottom-up control by enriching food resource. Unbalance fertilization could pose adverse on agricultural soil ecosystem and yield potential of crops.