Introduction

Cereal crops are very exhaustive and deplete soil nutrients in large quantities. In world, total more than half of the nitrogen fertilizer is consumed by cereals viz., rice, wheat and maize. Among all the nutrients, nitrogen is generally the most limiting nutrient under Indian conditions and its requirement for cereal crops may vary with soil, climate, genotypes and agronomic practices. Furthermore, in intensive cropping system farmers have liability to apply nitrogen in huge quantity to curtail production losses owing to soils degradation. Whereas, in areas with high rainfall and temperature, management of nitrogen poseses a great challenge in addition to losses of nitrogen. It can be achieved by following application of need based N on intermittent evaluation of crop N level and N application till the N level goes underneath a critical level.

To obtain the nitrogen status of standing crops, we need to monitor with different techniques to answer the questions of when, where, how much of fertilizers and how to apply the fertilizers. Thereby, techniques like use of leaf-colour chart (LCC), nutrient expert, a computer-based decision support tool (Kumar et al., 2014), chlorophyll meter (SPAD meter) are the better options to increase nitrogen-use efficiency and productivity of crops. Nevertheless, owing to its expensive cost and lack of knowledge; chlorophyll meter, nutrient expert, computer-based decision support tool usage by the farmers in developing countries is restricted. Keeping the foregoing fact in contemplate, recent days’ leaf colour chart (LCC) has been developed and it is ideal to farmers as a visible and subjective indicator of the crop N levels and can be used for precision nitrogen application (Ladha et al., 2000). 

Leaf colour chart (LCC) permit an expeditious and reliable watching of leaf greenness by visual appearance of spectral properties of leaves and also it is very simple and easy to use by the farmers. It acts as a better guide to the farmers for thoughtful and right time nitrogen application. LCC is an ideal tool to optimize N use in most of the cereal crops and it consists of series of four/six green coloured shades horizontally ranging from light yellowish green to dark green colour strips fabricated with veins resembling those of leaves that are used to compare with a leaf in the same light conditions. LCC is being used successfully in crops like rice (Witt et al.,2005), wheat (Singh et al., 2014) and maize (Naik et al., 2019) to evaluate the efficient N requirement under multiple situations of soil, climate and crop variety.

How to Use the LCC

1. A ‘four/six panel’ LCC can be used to counterpart leaf colour from ten disease and pest free plants in a field with uniform plant population.

2. Observations to be taken by placing the central part of the youngest completely expanded and healthy leaf on the top of the colour strips on the chart, and compare the leaf colour with the colour panel of the LCC.

3. Don’t remove and destroy the leaf/plant during observation.

4. During observation don’t expose LCC directly to sunlight and leaf being measured is to be shielded from the sun. LCC readings need to be taken at same time of the day (8.00-11.00 AM).

5. LCC readings should be taken by same member at the same time of the day.

6. Determine the average LCC reading for the selected leaves. When six or more leaves read below a critical LCC value (4.0 for rice and wheat and 5.0 for maize), urea can be applied for rectifying deficiency symptoms.

7. After flowering stage, use of LCC should be stopped.

Manual usage of LCC in maize

Manual usage of LCC at threshold 5.0

Variations in maize growth due LCC threshold 4.0

Variations in maize growth due LCC threshold 5.0

LCC Threshold Values for Different Crops

LCC threshold values for real time nitrogen management during vegetative growth in different cereal crops for getting higher yield and nitrogen savings are LCC threshold 4.0 for rice and wheat (Singh et al., 2014), whereas LCC threshold 5.0 for maize (Naik et al., 2019; Singh et al., 2014) along with basal dose of fertilizers.

Quantification of Nitrogen Saved Using LCC

Matching of fertilizer nitrogen supply with crop demand using various LCC threshold values are given in Table 1. Maize crop is highly exhaustive and requirement of nitrogen is very high and productivity of maize is higher at LCC threshold 5.0 by saving 55.3 kg N ha^-1.

Table 1: Quantity of fertilizer N applied and saved in various LCC threshold values

Effect on Economic Returns

Gross monetary returns, net   monetary   returns and returns per rupee invested play a major role, to persuade the farmers for acceptance of any clarified version of agro-techniques. Higher yields of maize crop with higher monetary returns were obtained with higher level of LCC threshold 5 (Table 2) and recorded significantly higher returns per rupee invested (2.32) than LCC 4.5 (2.16) and LCC 4 (2.03). These results indicated that LCC based fertilizer N management could be a perfect strategy that always gave a benefits of saving fertilizer N and producing more yield with same fertilizer. This might be due to higher yield in LCC based N application with higher dose and increased number (5) of split applications of N. Also the highest returns per rupee invested (1.94) was noticed in rice (Moharana et al., 2017).

Table 2: Gross monetary returns, net monetary returns and returns per rupee invested as influenced by various LCC threshold level

Conclusion

In most of the cereal crops application of fixed N as basal and split at one time is not sufficient for achieving more production and nitrogen use efficiency. Thereby, maximum productivity and net returns of crops like rice, wheat and maize can be obtained by precision application of N in various splits at LCC thresholds values of 4.0 for rice and wheat and 5.0 for maize. Also LCC can be used even by small or illiterate farmers as it is cheaper and farmer’s friendly N management tool. Therefore, blanket application of fixed dose of nitrogen fertilizers at fixed time intervals should be  restored with real time nitrogen management technology using LCC in cereals.

Reference

Kumar, V., Singh, A.K., Jat, S.L., Parihar, C.M., Pooniya, V., Sharma, S., Singh, B., 2014. Influence of site-specific nutrient management on growth and yield of maize under conservation tillage. Indian Journal of Agronomy 59(4), 657–660.

Ladha, J.K., Fischer, K.S., Hossain, M., Hobbs, P.R., Hardy, B., 2000. Improving the productivity and sustainability of rice-wheat systems of the Indo-Gangetic plains: A synthesis of NARS-IRRI partnership research. IRRI Discussion Paper Series. IRRI, Philippines 40, 31.

Moharana, S., Gulati, J.M.L., Jena, S.N., 2017. Effect of LCC based nitrogen application on growth and yield of rice varieties during dry season. Indian Journal of Agriculture Research 51(1), 49–53.

Naik, M.R., Hemalatha, S., Reddy, A.P.K., Madhuri, K.V., Umamahesh, V., 2019. Need based nitrogen management on growth attributes of Rabi maize using leaf colour chart under varied plant density. International Journal of Chemical Studies 7(3), 2591–2596.

Singh, V., Singh, B., Thind, H.S., Singh, Y., Gupta, R.K., Singh, S., Singh, M., Kaur, S., Singh, M., Brar, J.S., Singh, A., Singh, J., Kumar, A., Singh, S., Kaur, A., Balasubramanian, V., 2014. Evaluation of leaf colour chart for need-based nitrogen management in rice, maize and wheat in north-western India. Journal of Research Punjab Agricultural University 51(3 & 4), 239–245.

Witt, C., Pasuquin, J.M., Mutters, R., Buresh, R.J., 2005. New leaf colour chart for effective nitrogen management in rice. Better Crops 89(1), 36–39.