Nitrogen‐enriched compost application combined with plant growth‐promoting rhizobacteria (PGPR) improves seed quality and nutrient use efficiency of sunflower

Ecological benefits associated with plant growth‐promoting rhizobacteria (PGPR) inoculants offer a promising integrated nutrient management option to counteract plant nitrogen (N) deficiency. We performed field experiments to evaluate the effect of integrated N fertilizer regime involving chemical N fertilizer (CNF) and N‐enriched compost (NEC), either alone or combined with selected PGPR (Pseudomonas aeruginosa ) on sunflower seed quality, N use efficiency (NUE) and soil fertility during 2014–2015. We found that integrated N biofertilizer application resulted in significantly higher seed oil concentration, fatty acid composition, and harvest index in both cropping years. Greater effects on N yield efficiency (NYE), N use efficiency (NUE), N physiological efficiency (NPE), and photosynthetic N use efficiency (PNUE) were recorded in nitrogen‐enriched compost+PGPR inoculant (NECPI) treatment followed by chemical N fertilizer+PGPR inoculant (CNFPI) treatment. Statistically significant differences were observed in linoleic and linolenic acid, NYE, and NUE for treatment × year interaction, thus, suggesting that the integrated N biofertilizer approach facilitates the efficient N use by sunflower for improving yield and seed quality. Moreover, we also found considerable enhancement of soil N fertility after two consecutive cropping years of sunflower. The enhancement of seed quality, N use efficiencies, and soil N fertility through integrated N biofertilizer application emphasizes the importance of balanced crop N nutrition, ensuring sufficient N supply to sunflower with adequate N balance in soil for the next crop. Overall, combination of PGPR with NEC amendment may optimize N uptake efficiency and reduce N fertilizer losses, which is necessarily required for the sustainable sunflower production.     

Use of Plant-Growth-Promoting Rhizobacteria (PGPR) Seed Inoculation as Alternative Fertilizer Inputs in Wheat and Barley Production

In this study we aimed to investigate the effects of plant-growth-promoting rhizobacteria (PGPR) on seed incubation of spring wheat and barley. Three bacterial strains were applied singly and in combinations. Seed inoculation with strains significantly affected grain yield (GY), straw (SWY), total yield (TY), and plant nutrient element (PNE) content. In field trials, compared to the control, single inoculations gave GY, SWY, and TY increases by 27.5–31.9%, 1.1–5.3%, and 1.3–11.3% in wheat and 15.1–27.8%, 10.8–15.5%, and 14.5–18.5% in barley, respectively, but mixtures of strains gave increases in GY, SWY, and TY by 54.7%, 2.1%, and 6.7% in wheat and 57.8%, 14.6%, and 17.5% in barley, respectively. According to the results, it was concluded that seed inoculations with PGPR and mixture inoculation might satisfy nitrogen requirements, but Bacillus megaterium M3 and MIX (Bacillus subtilis OSU142, B. megaterium M3, Azospirillum brasilense Sp245) inoculation provided greater PNE concentrations than mineral fertilizer application for wheat and barley under field conditions.     

Boron Requirement of Irrigated Cotton in a Typic Haplocambid for Optimum Productivity and Seed Composition

Boron (B) deficiency hampers cotton (Gossypium hirsutum L.) growth and productivity globally, especially in calcareous soils. The crop is known as a heavy feeder of B; however, its reported plant analysis diagnostic norms for B-deficiency diagnosis vary drastically. In a 2-year field experiment on a B-deficient [hydrochloric acid (HCl)–extractable 0.47 mg B kg^?1], calcareous, Typic Haplocambid, we studied the impact of soil-applied B on cotton (cv. CIM-473) growth, productivity, plant tissue B concentration, and seed oil composition. Boron was applied at 0.0, 1.0, 1.5, 2.0, 2.5, and 3.0 kg B ha^?1, as borax (Na₂B₄O₇·10H₂O), in a randomized complete block design with four replications, along with recommended rates of nitrogen (N), phosphorus (P), potassium (K), and zinc (Zn). Boron use improved crop growth, decreased fruit shedding, and increased boll weight, leading to seed cotton yield increases up to 14.7% (P < 0.05). Improved B nutrition of plants also enhanced seed oil content (P < 0.05) and increased seed protein content (P < 0.05). Fiber quality was not affected. Fertilizer B use was highly cost-effective, with a value–cost ratio of 12.3:1 at 1 kg B ha^?1. Fertilizer B requirement for near-maximum (95% of maximum) seed cotton yield was 1.1 kg B ha^?1 and HCl-extractable soil B requirement for was 0.52 kg ha^?1. Leaf tissue B requirement varied with leaf age as well as with plant age. In 30-day plants (i.e., at squaring), B-deficiency diagnosis critical level was 45.0 mg kg^?1 in recently matured leaves and 38.0 mg kg^?1 in youngest open leaves; at 60 days old (i.e., at flowering), critical concentration was 55.0 mg kg^?1 in mature leaves and 43.0 mg kg^?1 in youngest leaves. With advancement in plant age critical B concentration decreased in both leaf tissues; that is, in 90-day-old plants (i.e., at boll formation) it was 43.0 mg kg^?1 in mature leaves and 35.0 mg kg^?1 in the youngest leaves. As critical concentration range was narrower in youngest leaves (i.e., 35–43 mg kg^?1) compared with mature leaves (i.e., 43–55 mg kg^?1), B concentration in youngest leaves is considered a better indicator for deficiency diagnosis.     

Zinc Fertilization Impact on Irrigated Cotton Grown in an Aridisol: Growth,Productivity, Fiber Quality,and Oil Quality

Zinc (Zn) deficiency is widespread in calcareous soils. Therefore, we conducted a 2-year field experiment to investigate the impact of graded Zn levels on growth, yield, and fiber and oil quality of cotton (Gossypium hirsutum L., cv. CIM-473) grown in a calcareous Aridisol having 0.54 mg diethylenetriaminepentaacetic acid (DTPA)-extractable Zn kg^?1 soil. Zinc use increased boll bearing, boll weight, seed index, and seed cotton yield (P ≤ 0.05). Maximum yield increase was 15%, with 7.5 kg Zn ha^?1; however, greater Zn levels depressed yield. Leaf chlorophyll, membrane permeability, seed protein, and oil content and quality improved (P ≤ 0.05), and fiber quality remained unaffected with Zn use. Critical Zn concentration in cotton leaves was 36 mg kg^?1. Positive relationships of leaf Zn concentration were observed with boll weight, protein content, total unsaturated fatty acids, and fiber characteristics. Thus, Zn fertilization of low-Zn Aridisols is suggested for improving cotton productivity and seed quality.     

Effects of irrigation sources on ammonia-oxidizing bacterial communities in a managed turf-covered aridisol

Ammonia-oxidizing bacteria (AOB) perform the rate-limiting step of nitrification, a key process in the global nitrogen cycle. In this study, chemical factors controlling AOB activity, diversity, and composition in a turfgrass-covered aridisol irrigated with groundwater, Colorado River water, or reclaimed wastewater were examined. Activity of AOB contributed an average of 96% of potential nitrification activity in four soils examined, and this activity correlated positively with ammonium concentration and negatively with salinity of the irrigation water. AOB abundance, as determined by quantitative polymerase chain reaction, also correlated positively with ammonium concentration in the irrigation water but negatively with soil salinity. Characterization of AOB communities by denaturing gradient gel electrophoresis showed the presence in every soil of AOB taxa, most commonly found in high-ammonia environments. The soil with the fewest years of management had the least diverse AOB population, compared to the other three soils, and much lower specific nitrification activity. This soil was irrigated with highly saline Colorado River water, which likely exerted acute negative effects on the activity of AOB. In summary, this study revealed that, although AOB activity and growth responded positively to ammonium availability in irrigation water, the salinity of the water and soil had strong negative effects on these aspects of the AOB community.