Crop yield and soil biochemical properties under different nitrogenfertilization and irrigation management schemes

It is generally known that nitrogen (N) and water are critical for crop growth. It is therefore important to study the effects of N fertilization and irrigation on crop yield, soil properties and their relationship to crop yield. However, domestic studies have provided little details about the relationship between crop yield and soil properties influenced by N fertilization and irrigation management schemes. Foreign studies have mainly focused on the relationship between soil physicochemical properties and crop yield, and the relationship of crop yield with soil biochemical properties not well documented. To address this knowledge gap, this study explored the effects of N fertilization and irrigation management schemes on crop yield and soil biochemical properties and their relationship. N fertilization and irrigation management schemes were initiated in 2005 at the Fengqiu Agro-Ecological Experimental Station of Chinese Academy of Sciences. Under summer maize (Zea mays L.) and winter wheat (Triticumae stivum L.) crop rotation system, N fertilizer was applied at the rates of 150 kg·hm^-2, 190 kg·hm^-2, 230 kg·hm^-2 and 270 kg·hm ^-2 per crop season and non-N input used as the control. Irrigation was done to meet soil field capacity of the 0 20 cm, 0 40 cm and 0 60 cm soil layers and also with rain-fed treatment as the control. Soil samples were collected at 0 20 cm soil depth in June 2011 and basal biochemical properties determined. Meanwhile, crop yield data for 2008 2011 were analyzed. The results showed that N fertilization rate of 150 270 kg·hm^-2 did not significantly enhance maize yield in 2008 and 2009, and wheat yield in 2009 and 2010. Irrigation little influenced maize yield in 2010, while maize yield in 2008 and 2009 gradually increased with increasing irrigation amount. Compared with rain-fed system, irrigation increased wheat yield in 2008 2011. N fertilization increased soil total N content (TN), available N content (AN), dehydrogenase activity (DHD), urease activity (URE), microbial biomass carbon content (MBC), basal soil respiration (BSR) and nitrification potential (NP) to varying degrees. N fertilization slightly decreased soil pH and sharply decreased available P content (AP) by 48.7% 51.6%. Irrigation slightly increased TN and DHD and then decreased URE, BSR, NP and total K content (TK) to varying degrees. With the exception of TK, AN, and DHD, correlation analysis showed significant correlations among these properties. Principal component analysis was used to select highly weighted factors for explaining yield variation. The selected properties included TN, DOC, AP, MBC, MBN, NP and quotient of respiration (qCO₂). After analyses using the determined biochemical properties, multi-collinearity problem was resolved. Finally, multiple linear regression analysis was performed using the selected properties (TN, DOC, AP, MBC, MBN, NP, qCO₂) and crop yield, in which all the regression equations of predicted maize yield in 2009 and 2010 were highly significant. In conclusion, differentiation of soil biochemical properties resulting from N fertilization and irrigation partly estimated crop yield. This research method provided the needed reference for selecting yield determinants and building yield models.