Effect of irrigation method and scheduling on development and water utilization in winter wheat

Abstract

A field experiment was carried out in winter wheat (Triticum aestivum L) during two consequent years 2013-2014 and 2014-2015 to study responses of soil and plant under currently practiced main irrigation methods with promising irrigation scheduling in the North China Plain (NCP). In this two factors experiment, sprinkler irrigation (SI), surface drip irrigation (SDI) and flood irrigation (FI) as three irrigation methods were scheduled to irrigate the crop as soon as the soil water content (SWC) decreases to 70%, 60% and 50% of field capacity (FC). Effects of both irrigation method and irrigation scheduling were studied to understand the phenomena occurred above and beneath the soil surface. With this aims the experiment were carried out to keep focus in determining the overall soil water dynamics, root morphological development, root water uptake, soil temperature, crop physiological growth and development along with yield parameters. Finally, the irrigation systems were evaluated on the basis of those studied parameters to determine the efficient, convenient and practical irrigation method and irrigation scheduling for winter wheat water management at NCP. The main results can be concluded as follows: The profile soil water dynamics for one dimensional movement of water were studied by using simulation model “Hydrous-1D”. Soil water content was highly influenced by irrigation water as well as by precipitation and found great variation at 0-40 cm soil layer depending on irrigation method and irrigation scheduling which finally determined the overall grain yield and yield attribute parameters beneath and above soil surface. Profile soil water content, which correspondingly changed with irrigation method and scheduling becomes the key factor in controlling overall irrigation water requirement by shifting the profile root water uptake (RWU). The daily RWU reached 6 to 9 mm/day at the end of March to mid of April and at early to mid of May. This can be hypothesized that winter wheat requires irrigation in this interval if there was no enough rainfall. It has found that top 20 cm soil layer established as main uptake region which supply 38-40% of total RWU where the existent of root length density (RLD) is higher. The uptake has been found increasing with increasing irrigation frequency for all irrigation method. The RWU leads by SDI compared to SI and FI in upper soil profile at all level of irrigation scheduling due to higher root length density (RLD) for SDI than SI and FI whereas, uptake leads in FI in deep soil profile below 60 cm as compared to SI and SDI. The ratio of evaporation (Es) to Evaporation (ET) decreases with increasing irrigation amount and found minimum in SDI because of minimal wetted surface parameter. Continuously measured soil temperature from March to harvesting shows that the temperature fluctuation occurred significantly on the surface soil and found more in SDI followed by SI. This cause frequent surface drying on the surface soil and create water stressed particularly in the treatment irrigating at 50% of FC. The maximum surface temperature fluctuation in SI at 50% irrigation scheduling treatment (IST) was found 4.3oC more than that in treatments scheduled to irrigate at 70% of FC, while compared different irrigation level within each irrigation method. Similarly, the greatest surface temperature floatation difference of 3.7oC was found between FI and SDI at 70% while comparing different irrigation method under similar irrigation level. The highest range of surface temperature fluctuation in SDI at 50% IST was found 5.4oC higher than that in FI at 70% IST when estimating temperature fluctuation difference among all individual irrigation treatments. The temperature at deeper soil profile was lowered gradually and temperature fluctuation becomes narrower among the treatments, which create a temperature gradient between surface and deeper soil profile. The root morphologies of winter wheat were studied by washing root method where the scanned roots were analyzed using WinRHIZO Reg. 2007d software throughout its growth period. The maximum root depth and root morphology was found at flowering for all treatment. In both cropping years SDI with 70% irrigation scheduling treatment (IST) produce denser root followed by FI in 2015 and by SI in 2014 in the top soil whereas, root growth lead by FI followed by SI with 50% IST below 60 cm soil profile. Lower irrigation rate in SDI keeps holding almost all irrigation water in upper 60 cm soil profile which causing to shift RLD upward and reduced drainage. The maximum RLD at flowering was found 41.05 cm.cm-3 in SDI followed by SI (38.29 cm.cm-3) with 70% IST in top 10 cm soil profile and RLD lead by FI (3.52 cm.cm-3) with 50% IST in 90-100 cm soil profile. The average diameter shown higher in FI (0.303 mm) followed by SDI (0.287 mm) irrigated at 50% of FC in 2015 crop season. More frequent irrigated treatment significantly increases the root biomass and similar trend was found for root volume and for projected area. The comparative studies on winter wheat yield components were carried out to determine the most efficient irrigation system. It has found that irrigation method with proper irrigation scheduling had potential to increase the yield components significantly and can be made the balance between the optimum yields with efficient utilization of irrigation water. It was estimated that 180.27 mm irrigation water (about 318.17 mm of total water including rainfall) is the optimal requirement to produce highest grain yield which can be achieved by 6 irrigations with 30 mm per irrigation by SDI or SI system or 3 irrigations with 60 mm per irrigation by FI system. On the other hand, water use efficiency (WUE) has estimated to gain maximum value with the irrigation amount of 154.53 mm. This shows that the maximum WUE can be achieved by irrigating winter wheat 5 times, 30 mm each with SDI or SI system and maximum of 3 times, 60 mm each with FI. While comparing the grain yields of different treatments, it has found that, maximum grain yield of 9.53 t ha-1 was received in SDI at 60% followed by 9.37 t ha-1 at 70% with same irrigation method and lowest 8.26 t ha-1 in FI at 50% of FC. Similarly SDI with 60% IST received maximum WUE of 2.08 kg m-3 followed by SI (2.05 kg m-3) with same irrigation level whereas, irrigating at 50% of FC with SI gains maximum irrigation water use efficiency (IWUE) of 9.38 kg m-3 followed by SDI (9.20 kg m-3) with same irrigation level. This concluded that SDI performed better to increase potential grain yield with higher WUE. In this way it can be revealed that either to achieve maximum grain yield or optimal WUE, the optimal irrigation scheduling and water application method should be chosen to assure irrigation water between 154.53 mm to 180.27 mm. This referred that irrigating winter wheat at 60% of FC will be most beneficial irrigation scheduling and SDI will be the best option to obtained potential grain yield, WUE and IWUE. This study strongly recommended to irrigate winter wheat with SDI system at 60% of FC even for dry season and suggested to select irrigation scheduling time according to local weather conditions.