Simulation of water and nitrogen dynamics as affected by drip fertigation strategies

The aim of drip fertigation is synchronising the application of water and nutrients with crop requirements, and maintaining the proper concentration and distribution of nutrient and water in the soil. The wetting patterns and nutrient distributions under drip fertigation have been proved to be closely related to the fertigation strategies. In order to find out the critical factors that affect the nutrient distribution under different drip fertigaiton strategies, a computer simulation model HYDRUS2D/3D was used to simulate the water and nitrate distribution for various fertigation strategies from a surface point source. Simulation results were compared with the observed ones from our previous studies. A 15° wedge-shaped plexiglass container was used in our experiment to represent one-twenty-fourth of the complete cylinder. The height of container is 40 cm, and the radius is 41 cm. The ammonium nitrate solution was added through a no. 7 needle connected to a Mariotte tube with a flexible hose. The soil water content, nitrate and ammonium concentrations were measured. The comparison of simulated and observed data demonstrated that the model performed reliably. The numerical analysis for various fertigation strategies from a surface point source showed that：（1） The total amount of irrigation water, the concentration of the fertilizer solution and the amount of pure water used to flush the pipeline after fertilizer solution application are the three critical factors influencing the distribution of water and fertilizer nitrogen in the soil.（2） The fresh water irrigation duration prior to fertigation has no obvious effect on nitrate distribution. The longer flushing time period after fertigation resulted in nitrate accumulation closer to the wetting front. From the point of avoiding the possibility of nitrate loss from the root zone, we recommended that the flushing time period should be as shorter as possible.（3） For a given amount of fertilizer, higher concentration of the fertilizer applied solution reduces the potential of nitrate leaching in drip irrigation system. While, lower concentration of the fertilizer solution resulted in an uniform distribution of nitrate band closer to the wetted front.

Optimizing the Irrigation Scheduling Strategy and the Water Use Efficiency in Steppe and Irrigated Crop Production Ecosystems in the Northwestern China

In an irrigation management problem, decisions are made at various levels for assessment of water availability and requirements, proposing the type of irrigation scheduling, and deriving an actual operational policy for various crop scenarios. In this study, a plan was developed for water management. A general strategy for planning and application of irrigation management was proposed. Since the Penman method was used, the focus was on a synthetic study involving basic project situations, relevant data, water requirement calculation, irrigation scheduling, and discussion on optimizing water use efficiency in the steppe and irrigated crop production ecosystems. Effective use of tabular displays made interpreting and analyzing results easier. Based on the statistical analysis between spring wheat water availability and water requirement, a new type of index called water niche suitability was proposed. The particular type of irrigation scheduling was based on this index together with concrete situation of irrigated areas. The research showed that there are great potentiality of water resources in optimizing Ningxia irrigation management. The irrigation scheduling in this paper was found to be reasonable and demonstrated that results could be used to assist in improving water management decisions in the northwestern China.

Soil Temperature and Maize Nitrogen Uptake Improvement Under Partial Root-Zone Drying Irrigation

Soil temperature is a major effective factor on the soil and plant biological properties.Irrigation can affect soil temperature and thereby induces a temperature effect on plant growth,which may result in an economic increase due to higher yield and plant nutrition.A ?eld experiment was carried out to investigate the effects of three irrigation strategies including full irrigation(FI),partial root-zone drying(PRD) and de?cit irrigation(DI) on soil temperature and the consequent results on the grain yield and N uptake of maize(Zea May L.).Soil temperature was measured by time domain re?ectometry(TDR) sensors during the 2010 growing season.Irrigation treatments were applied from 55 to 107 d after planting.The PRD treatment caused soil temperature to be in a favorable domain for a longer period(for over 60% of the measuring dates) as a consequent result of water movement to deeper soil layers compared with the other treatments;the PRD treatment also reduced soil temperature at deeper soil depths to below the maximum favorable soil temperature for maize root growth,which resulted in deeper root penetration due to both water availability and favorable soil temperature.Compared to the FI treatment,the PRD treatment increased root water uptake by 50% and caused no signi?cant reduction in total N uptake,while this was not observed in the DI treatment partially due to the negative temperature effect of DI on plant growth,which consequently affected the water and nutrient uptake.A longer vegetation period in the PRD treatment was observed due to higher leaf N concentrations and no signi?cant reduction in maize grain yield occurred in the PRD treatment,compared with those in the FI treatment.Based on the results,having 15.2% water saving during the whole growing season,the PRD irrigation would positively affect soil temperature and the water and nutrient uptake as a consequent,which thereby would prevent signi?cant reduction in maize grain yield.