Cereals have large nitrogen requirement, but the demand for fertilizer is variable. Divergence between the supply and requirement of nitrogen can potentially hamper the crop growth as well as the environment, resulting in poor nitrogen use efficiency leads to economic losses. A balance between supply and utilization is required to optimize crop growth, economic returns and to maintain environmental sustainability which can be solved through need based nitrogen management which is nothing but application of inputs is according to the needs of the farm. Spatial variability is present in the fields but often they receive a same dose of fertilizers because they are treated by farmers as a homogenous unit. Through need based strategies, farmers will supply nitrogen fertilizers according to the demand of the crop which reduce the losses of N fertilizer. A precision agriculture approach to address the disparate spatial N requirements across a field is the use of a variable rate application guided by crop canopy reflectance sensors. Sensors like SPAD chlorophyll meter, greenseeker, rapid SCAN etc are used for determining the nitrogen need of the field crops. Many researchers across the globe are working on standardization of these sensors for different growth stages of the crop. Precision input management in cereals is lacking at present in most of the growing areas. A good amount of information on crop nutrition is available, but information regarding need based N management is lacking. This article reviews the work done on need based nitrogen management strategies in cereals.

To identify the SPAD chlorophyll meter based nitrogen management strategy in wet direct seeded rice, a field experiment was conducted at Agriculture Research Farm, Bihar Agricultural University, Sabour, Bhagalpur, Bihar, India during Kharif 2018. The experiment was conducted in split plot design which consisted of three rice cultivars as main plot treatments: Sabour Ardhjal, Shushk Samrat & Shabhagi Dhan and four N management practices as sub-plot treatments: No N (control), Fixed time N management (FTNM), Real time N management (RTNM) and Adjustable dose of N management (ADNM). Results revealed that among the cultivars, the maximum grain yield was obtained in Shushk Samrat (3956 kg/ha) which was statistically at par with Shabhagi Dhan (3752 kg/ha) whereas lowest grain yield was obtained in Sabour Ardhjal (3213 kg/ha). Among the N management practices, highest grain yield (4177 kg/ha) was recorded in ADNM which was at par with grain yield of FTNM (4134 kg/ha). Maximum gross (Rs. 79,957 ha-1) and net (Rs. 48,681 ha-1), B: C ratio (1.56) were obtained in ADNM. So, higher yields as well as sustainability of ecosystems can be achieved by practicing ADNM in direct seeded rice.