Urea is the most popular and widely used nitrogenous fertilizer. High soil urease activity rapidly hydrolyses applied urea to ammonia which contributes to soil nitrogen (N) losses and reduces N use efficiency of crop plants. The ammonia losses can be minimized by the inhibition of soil urease activity which has been explored using various potential chemical inhibitors. However, the soil urease activity inhibition potential of plant extracts is rarely explored to date. In the present study, extracts of 35 plant materials were taken and evaluated against jack bean urease. Eleven extracts, showing >50% jack bean urease inhibition, were selected and further investigated in 13 soils collected from various districts of Punjab, Pakistan. Interestingly, except Capsicum annum, Melia azedarach, Citrus reticulata and Quercus infectoria, the plant extracts showed urease inhibition activities in soils, the extent of which was lower as compared to that observed in jack bean urease though. Maximum urea hydrolysis inhibition (70%) was noted with Vachellia nilotica which was 40% more than that of hydroquinone (50%) followed by that of Eucalyptus camaldulensis (24%). The extracts of V. nilotica and E. camaldulensis were coated on urea and applied to soil in the next step. At 21^st day, 239% and 116% more urea-N was recovered from soil treated with V. nilotica and E. camaldulensis extracts coated urea, respectively, as compared to uncoated urea. Conclusively, these results indicated that the coating of V. nilotica and E. camaldulensis extracts on urea prills prolonged urea persistence in soil owing to minimum urea hydrolysis, probably, the extracts of V. nilotica and E. camaldulensis showed their urease inhibition potential. The results of this study provide a base line for the identification of new soil urease inhibitor compounds from plant materials in future.

Nitrogen is an essential nutrient element required for optimum crop growth and yield. If a specific amount of nitrogen is not applied to crops, their yield is affected. Estimation of nitrogen level in crops is momentous to decide the nitrogen fertilization in crops. The amount of nitrogen in crops is measured through different techniques, including visual inspection of leaf color and texture and by laboratory analysis of plant leaves. Laboratory analysis-based techniques are more accurate than visual inspection, but they are costly, time-consuming, and require skilled laboratorian and precise equipment. Therefore, computer-based systems are required to estimate the amount of nitrogen in field crops. In this paper, a computer vision-based solution is introduced to solve this problem as well as to help farmers by providing an easier, cheaper, and faster approach for measuring nitrogen deficiency in crops. The system takes an image of the crop leaf as input and estimates the amount of nitrogen in it. The image is captured by placing the leaf on a specially designed slate that contains the reference green and yellow colors for that crop. The proposed algorithm automatically extracts the leaf from the image and computes its color similarity with the reference colors. In particular, we define a green color value (GCV) index from this analysis, which serves as a nitrogen indicator. We also present an evaluation of different color distance models to find a model able to accurately capture the color differences. The performance of the proposed system is evaluated on a Spinacia oleracea dataset. The results of the proposed system and laboratory analysis are highly correlated, which shows the effectiveness of the proposed system.

In alkaline calcareous soils, ammonia volatilization is the primary nitrogen (N) loss process, resulting in the reduced N use efficiency of crops. This study aimed at assessing the impact of different N sources for top dressing on ammonia volatilization, as well as their effects on wheat growth and yield over two years. In each year, half of the recommended N was applied as a basal dose using diammonium phosphate (DAP) and urea. The remaining half was top‐dressed 35 days after sowing with various sources: prilled urea (PU), granular urea (GU), ammonium sulfate (AS), and calcium ammonium nitrate (CAN) in the first year; PU, urea coated with a urease inhibitor from 20 g (VnU‐20) and 40 g (VnU‐40) leaves of Vachellia nilotica, biochar‐coated urea (BU), and urease inhibitor paraphenylenediamine‐coated urea (PPDU) in the second year. Ammonia volatilization losses were tracked for up to 12 weeks from sowing. Ammonia losses from basal‐applied N remained consistent in both years, comprising around 4% of the applied N. In the first year, top‐dressed AS resulted in the highest losses, followed by GU, while losses from urea and CAN were statistically similar. In the second year, coated fertilizers showed lower ammonia losses compared to PU, with VnU‐40 displaying the least losses, 48% less than PU. Nitrogen concentration in wheat grain and straw exhibited a negative correlation with ammonia losses. The choice of top‐dressed N source influenced tillering, biological, straw, and grain yields of wheat. In the first year, CAN provided maximum yield benefits, and in the second year, VnU‐20 exhibited 27% more grain yield than PU. These findings suggest that top dressing with coated urea, especially VnU‐20, has the potential to reduce ammonia losses, improve crop nitrogen status, and enhance economic yield compared to other nitrogen sources.

Field experiments were conducted in 2006–2007 and 2007–2008 to evaluate the effects of three calcium carbide (CaC₂) based formulations (slow release sources of acetylene and ethylene) - matrix-1 [(M-1)(21% CaC₂, 58% polyethylene and 21% plaster of paris)], matrix-2 [(M-2)(42% CaC₂, 48% polyethylene and 10% plaster of paris)] and paint coated [(PC)(35% CaC₂, 44% paint and 21% plaster of paris)] - on nitrification inhibition; growth, yield and nitrogen (N)-uptake of wheat. All the three CaC₂ formulations (CCF,s) inhibited nitrification, reduced plant height, and improved N-uptake, spike bearing tillers, 1000-grains weight and yield of Inqulab-91 and Bhakhar-02 wheat cultivars. Increase in grain yield was found maximum (22% over the control) with M-1 applied at 30 kg CaC₂ ha⁻¹; followed by M-2 and PC. Furthermore, CaC₂ significantly reduced lodging in Bhakhar-02 plots. It is concluded that grain yield of wheat can be enhanced by the application of CaC₂ formulations particularly M-1 along with NPK fertilizers.