Comparative assessment of soil fertility status of various agroecological regions under intensive cultivation in Northwest India.

Assessment of soil fertility status at agroecological region scale can help draw sound nutrient management and cropping plans for sustainable agriculture. It can also forewarn about emerging issues especially in regions under long-term intensive cropping. To meet this objective, 500 surface soil (0-15 cm) samples were collected from the five agroecological regions of Punjab state (India). The regions were Sub-mountainous Siwalik Hills (SSH), Northeastern Undulating (NEU), Piedmont and Alluvial Plain (PAP), Central Alluvial Plain (CAP), and Southwestern Alluvial Plain (SWAP) running from northeast Punjab to southwest Punjab in that order. Highest soil organic carbon (SOC) content (mean, 0.77%) was observed in the SSH region, despite it being dominated by coarse-textured soils (mean sand content 74.2%). The Piedmont and Alluvial Plain region showed the highest mean available potassium (K) content (mean 173.2 kg ha-1 with 76-865 kg ha-1 range) which can be attributed to K-rich mineralogy and higher K fertilizer use in the region. In contrast, relatively lower K levels in the Central Alluvial Plain region warned about K mining under predominant rice-wheat system. Higher electrical conductivity (EC, mean 0.95 dS m-1) values in the SWAP region and in some areas in the CAP region hinted at the risk of land degradation due to salinity. The study revealed impending micronutrient deficiencies in certain areas. Overall, the investigations suggested dominant influence of climate and parent material on fertility status with agronomic interventions mainly affecting distribution of P, K, and Zn only.

Novel Alleles of Phosphorus-Starvation Tolerance 1 Gene (PSTOL1) from Oryza rufipogon Confers High Phosphorus Uptake Efficiency.

Limited phosphorus availability in the soil is one of the major constraints to the growth and productivity of rice across Asian, African and South American countries, where 50% of the rice is grown under rain-fed systems on poor and problematic soils. With an aim to determine novel alleles for enhanced phosphorus uptake efficiency in wild species germplasm of rice Oryza rufipogon, we investigated phosphorus uptake1 (Pup1) locus with 11 previously reported SSR markers and sequence characterized the phosphorus-starvation tolerance 1 (PSTOL1) gene. In the present study, we screened 182 accessions of O. rufipogon along with Vandana as a positive control with SSR markers. From the analysis, it was inferred that all of the O. rufipogon accessions undertaken in this study had an insertion of 90 kb region, including Pup1-K46, a diagnostic marker for PSTOL1, however, it was absent among O. sativa cv. PR114, PR121, and PR122. The complete PSTOL1 gene was also sequenced in 67 representative accessions of O. rufipogon and Vandana as a positive control. From comparative sequence analysis, 53 mutations (52 SNPs and 1 nonsense mutation) were found in the PSTOL1 coding region, of which 28 were missense mutations and 10 corresponded to changes in the amino acid polarity. These 53 mutations correspond to 17 haplotypes, of these 6 were shared and 11 were scored only once. A major shared haplotype was observed among 44 accessions of O. rufipogon along with Vandana and Kasalath. Out of 17 haplotypes, accessions representing 8 haplotypes were grown under the phosphorus-deficient conditions in hydroponics for 60 days. Significant differences were observed in the root length and weight among all the genotypes when grown under phosphorus deficiency conditions as compared to the phosphorus sufficient conditions. The O. rufipogon accession IRGC 106506 from Laos performed significantly better, with 2.5 times higher root weight and phosphorus content as compared to the positive control Vandana. In terms of phosphorus uptake efficiency, the O. rufipogon accessions IRGC 104639, 104712, and 105569 also showed nearly two times higher phosphorus content than Vandana. Thus, these O. rufipogon accessions could be used as the potential donor for improving phosphorus uptake efficiency of elite rice cultivars.