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Nitrogen (N) and phosphorus (P) deficiency in soils limit plant growth. Consequently, chemical fertilizers are applied to fulfill crop nutrient demands. However, low nutrient utilization can make these fertilizers unprofitable for low-income smallholding farmers. Therefore, we studied the influence of Bradyrhizobium sp. and phosphate-solubilizing bacteria (Pseudomonas) on N and P utilization by mungbean crop from fertilized nutrient-deficient soil. We inoculated novel Bradyrhizobium sp. TAL-377 and Pseudomonas sp. 54RB strains alone or their combination with seeds of mungbean varieties (C-MUNG, NM-06, and NM-11). A basal dose of chemical fertilizers was applied at the rate of 60 kg N and 90 kg P ha−1 in the form of urea and single super phosphate in all plots before crop sowing. All inocula increased soil mineral N and P compared to control (P < 0.05). Co-inoculation increased mineral N by 30%, 18%, and 18% than Bradyrhizobium sp. alone and increase in P was 22, 29 and 43% than Pseudomonas sp. in C-MUNG, NM-06, and NM-11, respectively. This resulted in 35%, 45%, and 36% higher shoot N uptakes than Bradyrhizobium sp., and 46%, 84%, and 62% higher shoot P uptake than Pseudomonas sp. in the varieties. Similarly, root nodulation, mungbean grains, and biological yields were higher in co-inoculation treatments than single strain (p < .05). Hence, co-inoculation of Bradyrhizobium sp. and phosphorus solubilizing bacteria (Pseudomonas sp.) is a vital strategy to increase mungbean growth, yield, N and P utilization from chemical fertilizers applied in nutrient-deficient soils.

Currently, the global agriculture productivity is heavily relied on the use of chemical fertilizers. However, the low nutrient utilization efficiency (NUE) is the main obstacle for attaining higher crop productivity and reducing nutrients losses from these fertilizers to the environment. Coating fertilizer with micronutrients and biopolymer can offer an opportunity to overcome these fertilizers associated problems. Here, we coated urea with zinc sulphate (ZnS) and ZnS plus molasses (ZnSM) to control its N release, decrease the ammonia (NH3) volatilization and improve N utilization efficiency by sunflower. Morphological analysis confirmed a uniform coating layer formation of both formulations on urea granules. A slow release of N from ZnS and ZnSM was observed in water. After soil application, ZnSM decreased the NH3 emission by 38% compared to uncoated urea. Most of the soil parameters did not differ between ZnS and uncoated urea treatment. Microbial biomass N and Zn in ZnSM were 125 and 107% higher than uncoated urea, respectively. Soil mineral N in ZnSM was 21% higher than uncoated urea. Such controlled nutrient availability in the soil resulted in higher sunflower grain yield (53%), N (80%) and Zn (126%) uptakes from ZnSM than uncoated fertilizer. Hence, coating biopolymer with Zn on urea did not only increase the sunflower yield and N utilization efficiency but also meet the micronutrient Zn demand of sunflower. Therefore, coating urea with Zn plus biopolymer is recommended to fertilizer production companies for improving NUE, crop yield and reducing urea N losses to the environment in addition to fulfil crop micronutrient demand.

The low nitrogen utilization efficiency (NUE) of commercial fertilizers is one of the main hurdles in higher crop production and reduction of fertilizer N losses to the environment. However, interactions between most the macronutrients could have synergistic outcomes that affect crop NUE. The coating of urea with macronutrients and biopolymers may control N release and synergistically impact its crop NUE. In this study, urea was coated with 3% of different polymers, combined with 5% potassium iodide (KI) (i) Gum Arabica (GA + KI), (ii) polyvinyl alcohol (PVA + KI), and (iii) gelatin (Gelatin + KI) to control its N release, leaching, and increase of wheat NUE. Scanning electron microscopy, Fourier Transform Infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses confirmed the successful coating of all KI and biopolymer combinations on urea granules. All coating combinations slowed down urea release in water and reduced its leaching from the soil, but the highest reduction in both parameters was observed with the GA + KI treatment, compared to the uncoated urea. After soil application, GA + KI decreased urea leaching by 26% than the uncoated urea in lysimeter. In the field, soil mineral N remained significantly high with the GA + KI and PVA + KI treatments at the wheat tillering, booting, grain filling and maturity stages, compared to the uncoated urea. However, K content was only high (28%) with the GA + KI treatment at final harvest. Likewise, microbial biomass N was only high with GA + KI at grain filling (20%) and maturity stages (24%) than the uncoated urea. Such synchronized N availability led to high wheat grain yield (28%), N (56%) uptake, and apparent N recovery (130%) with the GA + KI treatment, compared to the uncoated fertilizer. The increment in NUE with GA + KI could be due to the synergistic effect of K on N availability, therefore, we observed higher wheat yield and N utilization efficiency with this treatment. Hence, urea coated with macronutrient (K) plus biopolymer is recommended to improve wheat yield, NUE, and for reduction of environmental N losses.