الفهرس 
Improving Nitrogen Fertilizer Use Efficiency For Maize Using Active Optical Sensors
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Abstract
Sensor-based nitrogen (N) management techniques hold the promise of increasing N fertilizer use efficiency while decreasing the quantity of lost N reaching the environment. Two years’ field study was conducted at the Agricultural Research Station of Faculty of Agriculture, Cairo University at Giza, Egypt during 2019 and 2020 seasons on maize (Zea mays L.) to improve N fertilizer use efficiency using active optical sensors. The first season consisted of N fertilizer levels from 0 to 280 kg N ha-1 in three split doses to create variability in plant growth. The experimental design was randomized complete block design in three replications. The multi-rate N fertilizer treatments produced a high degree of grain yield and N uptake variability in the first season of experiment. Readings of GreenSeeker and atLeaf optical sensors were collected at V9 growth stage (around 50 days after sowing) of maize. This variability allowed developing algorithms to use the optical sensors in fine-tuning N fertilization in maize. In the second season, prescriptive N management, consisting of the application of 95, 190 or 142 kg N ha-1 at different times, combined with corrective N management driven by the developed algorithm in this study based on GreenSeeker sensor was employed.
Application of 71 kg N ha-1 at sowing and 71 kg N ha-1 at 30 days after sowing following a corrective dose based on GreenSeeker sensor produced the highly statistical grain yield (9695 kg ha-1) and nitrogen recovery efficiency (71.4%). Pertaining to atLeaf meter, the Cate-Nelson graph method was used to define the critical atLeaf meter index value at relative grain yield of 100, 80, and 70 %. These values were suggested to apply an increment doses of N fertilizer at V9 growth stage. The graph suggested that the critical values of chlorophyll index at 100, 80 and 70 % relative grain yield of maize were 60, 55 and 40, respectively. applying a total of 142 kg N ha-1 as prescriptive in two doses (71 and 71 kg ha-1) then applying a corrective dose as guided by the atLeaf meter at V9 growth stage resulted in grain yield of 9734 kg ha-1. Data pertaining to N recovery efficiency show that the meter-guided N treatments results in higher use efficiency as compared to the general recommendation. When appropriate prescriptive N fertilizer was applied (71and 71 kg N ha-1) followed by corrective dose, an average increase of 10.7% REN compared with the general recommendation. Therefore, using the chlorophyll meter in guiding N management could effectively manage N fertilizer in order to obtain higher yield along with high N use efficiency. This study revealed that N fertilizer could be managed more efficiently using tools like active optical sensors compared with the current general recommendation