Effects of fertigation strategies on water and nitrogen distribution under water storage pit irrigation for orchards

Water storage pit(WSP)irrigation is a simple and inexpensive technology suitable for orchards in semiarid and arid regions of North China.This study compared the effects of different fertigation strategies on water and nitrogen distribution,and ammonia volatilization.A fertigation experiment was conducted using a 30°wedge-shaped plexiglass soil container,which represents one-twelfth of the complete storage pit.The height of the container was 120 cm,and a plexiglass damper for simulating the zero flux plane of adjacent water storage pits was located at the 40 cm radius.Four fertigation strategies were used for WSP irrigation:solution application during the first half(N-W),the last half(W-N),the middle half of an irrigation cycle(W-N-W),and during the entire irrigation(N-N).Surface(SF)irrigation was used as a control treatment with solution application during the entire irrigation(SN-N).The experimental results showed that the soil water and ammonium contents at 0-10 cm soil depth under WSP irrigation were only 10.51%and 18.42% of those under SF irrigation,respectively.The cumulative NH3 volatilization under WSP irrigation was 51.71%-68.72% lower compared with that under SF irrigation.The soil water distributions were similar for all four fertigation strategies.NH3 volatilization mainly occurred at the pit wall interface,and cumulative NH3 volatilization loss followed the trend N-N>W-N>W-N-W>N-W.Ammonium was adsorbed into the soil and thus mostly remained near the pit wall.Low concentrations of ammonium were found near the edge of the wetting zone under all strategies.Compared to N-W,N-N and W-N-W treatments,W-N treatment decreased the nitrate accumulation at 80-90 cm by 38.6%,19.0%and 10.3%,respectively.The W-N strategy was suggested for minimizing potential nitrate leaching.

Modelling soil water dynamics and root water uptake for apple trees under water storage pit irrigation

Water storage pit irrigation is a new method suitable for apple trees.It comes with advantages such as water saving,water retention and drought resistance.A precise study of soil water movement and root water uptake is essential to analyse and show the advantages of the method.In this study,a mathematical model(WSPI-WR model)for 3D soil water movement and root water uptake under water storage pit irrigation was established based on soil water dynamics and soil moisture and root distributions.Moreover,this model also considers the soil evaporation,pit wall evaporation and water level variation in the pit.The finite element method was used to solve the model,and the law of mass conservation was used to analyse the water level variation.The model was validated by experimental data of the sap flow of apple trees and soil moisture in the orchard.Results showed that the WSPI-WR model is highly accurate in simulating the root water uptake and soil water distributions.The WSPI-WR model can be used to simulate root water uptake and soil water movement under water storage pit irrigation.The simulation showed that orchard soil water content and root water uptake rate centers on the storage pit with an ellipsoid distribution.The maximum distribution region of soil water and root water uptake rate was near the bottom of the pit.Distribution can reduce soil evaporation in the orchard and improve the soil water use efficiency in the middle-deep soil.

Urease activity and urea hydrolysis rate under coupling effects of moisture content,temperature,and nitrogen application rate

The traditional qualitative analysis of the individual factors on the kinetic parameters cannot sufficiently reveal the mechanism underlying urea hydrolysis in soil.This study aimed at revealing the coupling effects of the three factors on urease activity(V_(0)),hydrolysis rate constant(K_(u)),and activation energy(Ea)and establishing the quantitative model for K_(u) under the coupling condition.Laboratory culture experiments were conducted under different temperatures(T)(15℃,20℃,25℃,and 35℃),moisture contents(θ)(60%,80%,and 100%of field capacities),and nitrogen application rates(F)(247 mg/kg,309 mg/kg,371 mg/kg,and 433 mg/kg).The urea content was measured daily.Results showed that the effects of moisture content,temperature,nitrogen application rate,and their interaction on V_(0) and K_(u) were in the descending order:T,F,T^(*)F,θ,T^(*)θ,F^(*)θ,T^(*)θ^(*)F.The effect of single factor and two-factor coupling on V_(0) was extremely significant(p<0.01),whereas the effect of the three-factor coupling on V_(0) was negligible.The effects of three factors and their interaction on K_(u) were extremely significant(p<0.01).The effects of moisture content,nitrogen application rate,and their interaction on Ea were in the descending order:F,θ,F^(*)θ.The effects of two factors and their interaction on Ea were not significant.The mean absolute percentage error(MAPE)values of the established K_(u-1)(θ,T,F)and K_(u-2)(θ,T,F)models were 3.14%and 4.60%,respectively.The MAPE of the traditional Arrhenius model K_(u-3)(T)was 6.75%.The accuracy of the proposed three-factor interaction model was superior to that of the traditional single factor model.The results supplemented the mechanism of urea hydrolysis and improved the prediction accuracy of K_(u).