Effects of different low limits of irrigation on nutrients, enzyme activity and glomalin-rela-ted soil protein in soil aggregates of drip irrigation under plastic film.

Abstract

Irrigation is the main source of soil water in greenhouse. There is a lack of understanding on the effects of drip irrigation under the plastic film on the distribution characteristics of soil nutrients, enzyme activity and glomalin-related soil protein (GRSP) in soil aggregates. The effects of different irrigation low limits (20 kPa, D20; 30 kPa, D30; 40 kPa, D40) on soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), urease activity, invertase activity and GRSP in soil aggregates were investigated under the greenhouse with the continuously six years' irrigation. The results showed that compared with D20 and D40 treatments, D30 treatment significantly decreased the proportion of micro-aggregate (<0.25 mm), increased the proportion of macro-aggregate (>0.25 mm), and improved the mean mass diameter (MWD) by 26.4% and 13.4%, respectively. The concentrations of SOC, TN, TP and GRSP were relatively higher in 2-1 mm, 1-0.25 mm, and <0.053 mm aggregates. About 46.5% of SOC, 53.3% of TN and 37.7% of TP were distributed in the 1-0.25 mm aggregates. The urease and invertase activities were increased with the decreases in the size of aggregates, which were significantly increased in D30 and D40 treatments. The 1-0.25 mm aggregates had highest contributions to enzyme activities, with 38.7% of urease and 41.2% of invertase in bulk soil. Results from the correlation analysis showed that MWD was highly positively correlated with GRSP, SOC and urease activity, and the concentration of GRSP was highly positively correlated with SOC and urease activity. Therefore, the irrigation low limits of 30 kPa promoted soil aggregate stability and protection of soil aggregates to nutrients, enzyme activities and GRSP in greenhouse.