South and Southeast Kazakhstan underwent soil nitrogen forecasting and diagnosing for nutrition to establish the requirement of nitrogen fertilizers for field crops. The study established the possible use of alkaline hydrolyzable nitrogen as an indicator to provide field crops with available soil nitrogen. Managing the soil organic matter more accurately as the main source of nitrogen helps determine the spatial and temporal variability of its content in each specific field and to use a narrower (oriented to the prevailing soil types) scale of humus availability. The recent studies began in several stages, during 2014–2016, 2015–2017, and 2020–2021, on the irrigated light chestnut calcareous medium loamy non-saline and non-alkaline soil formed at the foothill loess plain of the Zailiyskiy Alatau, Kazakhstan. The nitrogen content of nitrates varied significantly over the years of research. In the control variants (without fertilizers), the recording of the minimum content of N-NO3 took place in 2016 compared with 2014 and 2015. In two consecutive years (2020–2021), 2,816 ha of arable land underwent testing in Almaty, Zhambyl, and Zhetysu regions, Kazakhstan. A total collection of 1,015 soil samples went through analysis, revealing a close correlation between the content of humus and alkaline hydrolyzable nitrogen in the upper soil layer of 0-30 cm. The hydrothermal conditions from a long multi-factorial field experiment data largely affected the intensity of mineralization and immobilization processes of the available nitrogen compounds. The rational use of nitrogen fertilizers makes it possible to increase the field crop yield with good quality and enhance the payback of applied fertilizers, maintaining and improving soil fertility.