Rice crop residue as fertiliser substitute for enhancing yield and soil health: Identifying the optimum level from multilocation trials in India

To address agricultural challenges like residue burning and excessive inorganic fertilizer use, a two-year (2023–2024) multi-location field experiment was conducted across five diverse Indian agro-ecological zones. Six integrated nutrient management strategies were tested: T1 (100% Recommended Dose of Fertilizers (RDF)), T2 (50% RDF + 50% RDF via residue), T3 (50% RDF + 50% RDF via residue + Pusa decomposer (PD)), T4 (50% RDF via residue + 50% RDF via green manure/green leaf manure), T5 (75% RDF + 25% via residue + PD), and T6 (control). Conventional fertilization (T1) consistently achieved the highest mean grain yield across locations. However, T5 (25% RDF substitution via crop residue) produced statistically comparable yields to T1, even surpassing it by 7.6% at Moncompu. Treatments T2 and T3 generally incurred yield penalties (10–28%), except at Karaikal, where T2 increased yield (+5% in 2023; +11.6% in 2024), due to favorable decomposition conditions. Despite yield trade-offs, T2 and T3 (50% RDF substitution via crop residue) exhibited superior yield stability across locations. Soil nutrient dynamics varied considerably by location and treatment. While T2 and T3 caused partial phosphorus (P) depletion, they consistently improved soil potassium (K) and organic carbon (OC). P buildup was seen in T2/T5 at Karaikal and T1-T5 at Pusa. Similarly, K buildup was seen across most treatments and sites, though K mining was widespread at Pantnagar. Nitrogen (N) and OC showed mixed results, with some treatments leading to accumulation and others depletion. The T6 consistently showed the highest nutrient depletion across all parameters. T1 yielded the highest partial factor productivity of nitrogen (PFP-N) at 47 kg grain/kg N, closely followed by T5 (44 kg grain/kg N). T3 (42.5 kg grain/kg N) was statistically similar to T5, establishing a PFP-N hierarchy of T1 > T5 ≈ T3 > T2 ≈ T4. Grain yield correlated positively with agronomic traits like tiller number, panicle density, and 1000-grain weight, all linked to N and K availability. Thus, co-application of 75% RDF via fertilizers and 25% using crop residues with microbial decomposers (T5) is recommended as a sustainable alternative integrated approach to conventional fertilization

Quorum Sensing Signaling Molecules Produced by Reference and Emerging Soft-Rot Bacteria (Dickeya and Pectobacterium spp.)

International audienceBACKGROUND: Several small diffusible molecules are involved in bacterial quorum sensing and virulence. The production of autoinducers-1 and -2, quinolone, indole and γ-amino butyrate signaling molecules was investigated in a set of soft-rot bacteria belonging to six Dickeya or Pectobacterium species including recent or emerging potato isolates. METHODOLOGY/PRINCIPAL FINDINGS: Using bacterial biosensors, immunoassay, and chromatographic analysis, we showed that soft-rot bacteria have the common ability to produce transiently during their exponential phase of growth the N-3-oxo-hexanoyl- or the N-3-oxo-octanoyl-l-homoserine lactones and a molecule of the autoinducer-2 family. Dickeya spp. produced in addition the indole-3-acetic acid in tryptophan-rich conditions. All these signaling molecules have been identified for the first time in the novel Dickeya solani species. In contrast, quinolone and γ-amino butyrate signals were not identified and the corresponding synthases are not present in the available genomes of soft-rot bacteria. To determine if the variations of signal production according to growth phase could result from expression modifications of the corresponding synthase gene, the respective mRNA levels were estimated by reverse transcriptase-PCR. While the N-acyl-homoserine lactone production is systematically correlated to the synthase expression, that of the autoinducer-2 follows the expression of an enzyme upstream in the activated methyl cycle and providing its precursor, rather than the expression of its own synthase. CONCLUSIONS/SIGNIFICANCE: Despite sharing the S-adenosylmethionine precursor, no strong link was detected between the production kinetics or metabolic pathways of autoinducers-1 and -2. In contrast, the signaling pathway of autoinducer-2 seems to be switched off by the indole-3-acetic acid pathway under tryptophan control. It therefore appears that the two genera of soft-rot bacteria have similarities but also differences in the mechanisms of communication via the diffusible molecules. Our results designate autoinducer-1 lactones as the main targets for a global biocontrol of soft-rot bacteria communications, including those of emerging isolates