Manjeet SinghMirzakhaninafchi, Hasan2020-11-122020-11-122020Mirzakhaninafchi, Hasan (2020). Design, development and evaluation of a variable rate applicator for real time application of fertilizer (Unpublished Ph.D. Dissertation). Punjab Agricultural University, Ludhiana, Punjab, India.https://krishikosh.egranth.ac.in/handle/1/5810154995There is a strong need to avoid use of excessive N as it is unlikely to be effective in increasing crop yields because of its diminishing returns. Therefore, a study was conducted to design and develop a variable rate fertilizer applicator to detect real time deficiency of nitrogen in the field and applying it as per requirement of the crop. To design and develop variable rate applicator, fluted roller type metering mechanism was selected due to having more uniformity than spinner disc type applicator. Suitable nitrogen (N) sensor i.e. Greenseeker was selected for the development of applicator. The microcontroller system was developed and PWM valve was used to vary the rotational speed of hydraulic motor resulting variation in the rotation of metering mechanism shaft. Field performance of the developed machine was measured at different levels of nitrogen (kg/ha), height (cm) of sensor from the crop canopy and at different growth stages of the crop. Fluted roller type metering mechanism was selected having lesser variation (CV ranging from 6.0 to 8.0 %) in fertilizer rate applied as compared to the spinner disc type fertilizer applicator having CV ranging from 20.0-50.0 %. Fertilizer rate at 10 rpm of metering mechanism shaft was minimum i.e. 15.18 kg/ha and was maximum 54.38 kg/ha at 40 rpm of the shaft speed. Speed of shaft of metering mechanism changed from 0 to 40 rpm when NDVI was changing from 0.75 to 0.35. The response time of the control system to apply fertilizer in the field was within the range of 6.45 to 7.81 s. Applied fertilizer by using developed variable rate applicator at different growth stages of the rice crop at 40, 60 and 80 DAT indicated that when fertilizer rate is increasing from N1 to N4, NDVI is increasing from 0.49 to 0.69. Hence, shaft speed is decreasing from 27 to 7 rpm to apply the fertilizer rate 35.47 to 9.00 kg/ha respectively. Total fertilizer applied by variable rate applicator was 122.32 kg/ha instead of 225 kg/ha as recommended by the university resulting 45% saving in fertilizer by using developed variable rate applicator.EnglishThesis