Effects Of Fertilization Systems On A Clayey Red Soil Properties And Maize Crop Water Relations

Red soils (equivalent to Ultisol) in southern China have poor physical and chemical properties and low fertility. The plants in red soil are often suffered from soil water stress due to seasonal drought. Poor soil properties and seasonal drought are the main limiting factors for agricultural production in red soil region. Fertilization systems and field managements are important in improving soil properties and stimulating plant growth. Thus, the soil and plant water relationship could be also regulated by the fertilization systems. It is essential to discuss how the soil-plant-water continuum is changed with fertilization system in red soil region of China.A long-term field experiment has been conducted since 1998 in the Red Soil Experimental Station, located in Xianning, Hubei, to investigate the effects of a control treatment (CK), application of chemical fertilizers (NPK), application of organic fertilizers it includes pig manure and chicken manure (OM), and NPK fertilizers plus straw returning (NPK+S) on a clayey red soil properties and maize crop water relations. The experiment was laid out according to a completely randomized block design with four replicates, for a total of 16 experimental plots. Summer maize and winter wheat were rotated. Plots were manual cultivated to 15 cm depth by shovel at seeding time. Four rows of maize were sown at a depth of 5 cm on July 2014.During the growth stage of maize crop, soil water content was measured at 0-10 cm, 10-20 cm,20-30 cm, and 30-40 cm. At the same time, soil penetration resistance was measured, which was inserted to 40 cm depth of the soil and the penetration resistance values were read at 2.5 cm interval. Measure the saturated hydraulic conductivity in the laboratory using the constant-head method. The soil water potentials were measured through a field of soil water content and soil water characteristic curve, combined with VG equation. Leaf and root potential was measured by Pressure Chamber Instrument. Leaf temperature, maize morphology, yield and weather condition were measured at intervals time during maize growth. After the maize was harvested, unsaturated hydraulic conductivity was measured, each measurement at a given water pressure head was replicated three times (runs). At the same time, above-and below-ground dry matters were measured and nutrients accumulation. The main findings are showed as follows:Results showed that OM significantly increased soil water retention capacity at all tensions but with larger increment in low tension at depths of 0-10 cm and 10-20 cm (P< 0.05) when compared with the CK. On the contrary, NPK and NPK+S led to a decrease in soil water retention capacity under chemical treatments. In the field both in wet and dry periods, soil water content was significantly higher in OM than in NPK+S and NPK (P <0.05), since unsaturated hydraulic conductivity are lower in OM than in other treatments. In contrast, the saturated hydraulic conductivity is higher in OM when compared with other treatments (P<0.05). OM was also found to have the lowest soil bulk density and penetration resistance and higher total porosity of the four treatments. In this study, OM treatment substantially influenced on the soil carbon content in the plow layer (0-20 cm), compared with the CK, inorganic fertilizers alone markedly affected the carbon content only in the 10 cm soil layer. The high negative correlation was observed between the soil organic carbon and the bulk density and the penetration resistance (P<0.01). Soil nutrient contents increased considerably in the fertilization treatments compared with CK, especially in OM and NPK+S, suggesting that organic and chemical fertilizer are, beneficial to the accumulation of soil nutrients. Moreover, studies showed that the soil pH in CK was lower than the initial value.With respect to growth character, it was observed that the plant height, stem diameter, leaf area and leaf area index increased significantly with organic and inorganic treatment than in the control. The highest maize grain yields were obtained with fertilization treatments. The NPK+S treatment has positive effect on grain yield followed by OM and NPK treatments when compared with CK (P<0.05). In contrast, OM treatment has higher effects on biological yield than in NPK+S and NPK treatments. The application of fertilization gained the highest ear characteristics of maize. The fertilization treatments has also positive effect on root mass density and root layer depth during growing season than in CK (P<0.05). NPK+S have higher effects on root dry weight than OM, NPK and CK. OM had greater in P and N concentration than in NPK+S, NPK and CK (P<0.05). The highest dry matter was obtained with fertilization systems in maize root, stem and leaf. OM has positive effect on dry matter, followed by NPK+S and NPK compared with CK (P<0.05).OM and NPK+S resulted in the reduced soil penetration resistance and increase soil water content. The results show that there was negative correlation between grain yield and crop water stress index (CWSI) when the crop water stress exceeded the drought threshold. However, the correlation between grain yield and CWSI was migrated by increasing the slope of the negative regression equation due to increasing NPK+S treatment. The present study showed that NPK+S treatment had a greater value of CWSI under strong to severe soil drought condition. The NPK+S presented less oscillation in the CWSI values which were maintained close to the zero level. The variations in CWSI under different water stress conditions during the growing season with increasing water stress, the values of CWSI all show the trend of increase; however, there are day-to-day variations of CWSI frequently. The average values of CWSI were significantly low in fertilization treatments, when compared with the control (P<0.05).The average of CWSI show that the NPK, OM and NPK+S fertilizers were significant effects on the CWSI in the slight to moderate water stress. The Maize yield decreases as the CWSI increases. The CWSI showed a negative correlation (p<0.01) with grain yield. The results suggest that we can use CWSI to monitoring long-term drought at farmland in red soil areas, and it can be used to estimate the final yield of maize.Data analysis shows that in a maize growth period, there was an obvious fluctuation of soil water potentials among treatments. OM treatment had greater soil water potential than NPK and NPK+S (P<0.05). The addition of OM increased the water potential of the soils in all treatments as any particular soil water content corresponds to a higher negative soil water tension. On the other hand, the effects of OM on improving soil water potentials reduced. Fluctuation soil water potentials reveal pore size distribution. The OM treatment has positive effect on root water potential during growing season when compared with CK (P<0.05), related with decreased of soil water content and increased penetration resistance. OM treatment had greater leaf water potential than NPK and NPK+S (P<0.05). The size of the sorting system under different fertilizer for OM> NPK+S> NPK> CK, substantially increases with soil penetration resistance decreases. Also the leaf water content was increases with differences increase between treatments, and the difference with the increased and gradually become larger. Dynamic changes of atmospheric water potential in maize growth stage depend on fluctuations in air temperature and relative air humidity; it reflects a change in the atmosphere water potential in during growing period. There were significant differences between all dates and lower moisture during the performance of the most obvious. The average atmosphere water potential was significant between all dates (P<0.05). It has been found increased in the atmosphere water potential after the first decline values, depending on changes in temperature and relative humidity.The long-term applications of OM and NPK+S were helpful to improving red soil properties and above-and below-ground Maize performance. As well as were improving soil water potential, plant water potential and CWSI. On the other hand, OM and NPK+S resulted in the reduced soil penetration resistance and increase soil water content, thus improved crop-water relations. Therefore, increased the crop growth and this helpful to reduce the seasonal drought in red soil.