Effects of controlled drainage on crop yield, drainage water quantity and quality: A meta-analysis

Abstract It is widely reported that controlled drainage (CD) has the potential to reduce outflow and increase crop yield. However, many researchers demonstrated that the percentage changes in crop yield, drainage water quantity and quality to CD use were variable. A total of sixty-one studies with 1050 data pairs were collected investigating ten main variables (yield, drainage volume, the concentrations and losses of N O 3 − - N , N H 4 + - N , total nitrogen (TN) and total phosphorus (TP)), and then a meta-analysis was conducted to: (1) estimate the effects of CD on crop yield, drainage water quantity and quality; (2) identify cropping system (paddy rice or dry land crops), drainage method (surface drainage or subsurface drainage) and climate type (based on the updated Koppen-Geiger climate classification) that benefit yield and drainage water quality under CD. Results showed that CD increased crop yield by 0.11%, decreased drainage volume by 19.23%, and reduced the concentrations and losses of all variables mentioned except for N H 4 + - N concentration and TP concentration. Dry land crop yield slightly increased while paddy rice yield significantly decreased, and the crop yield in the cold (D) climate increased but that in the temperate (C) climate decreased. The reduction of drainage volume was obvious except for dry land crop in surface drainage. N O 3 − - N concentration decreased to varying degrees and larger responses were found in dry land crop, subsurface drainage, and arid (B) or cold (D) climates. CD could greatly alleviate N O 3 − - N loss except dry land crop in surface drainage. Different extent increases in N H 4 + - N concentration were revealed except surface drainage while N H 4 + - N loss was on average 18.9% lower in CD than in the control. TP loss decreased with the exception of surface drainage. Our findings illustrated the advantages of the CD technique and provided suggestions for the rational application of CD.