Depth dynamics of soil N contents and natural abundances of 15N after 43 years of long-term fertilization and liming in sub-tropical Alfisol

The aim of this study was to understand impacts of long-term (43 years) fertilization on soil aggregation, N accumulation rates and δ¹⁵N in surface and deep layers in an Alfisol. Soil samples from seven treatments were analysed for N stocks, aggregate-associated N in 0–30 cm and the changes in δ¹⁵N in 0–90 cm depths. The treatments were: unfertilized control (control); recommended N dose (N); recommended N and phosphorus doses (NP); recommended N, P and potassium doses (NPK); 150% of recommended N, P and K doses (150% NPK); NPK + 10 Mg FYM ha^?1 (NPK + FYM) and NPK + 0.4 Mg lime ha^?1 (NPK + L). Results revealed that plots under NPK + FYM had ~39% higher total N concentrations than NPK + L in 0–30 cm soil layers. In NPK + L, macro-aggregates had 35 and 11% and microaggregates had 20 and 9% lower δ¹⁵N values than NPK + FYM in 0–15 and 15–30 cm soil layers, respectively. However, plots receiving NPK + FYM had ~39% greater deep soil (30–90 cm) N accumulation than NPK + L. These results would help understanding N supplying capacity by long-term fertilization and assist devising N management strategies in sub-tropical acidic Alfisols.     

Improving nitrogen and phosphorus use efficiencies through inclusion of forage cowpea in the rice–wheat systems in the Indo-Gangetic Plains of India

In high productivity zones of Indo-Gangetic Plains in south Asia, the rice–wheat system is stressed due to production fatigue as evidenced by declining soil organic matter content, low efficiency of fertilizer use and diminishing rates of factor productivity. We, therefore, conducted field experiments at Modipuram, India, to conserve soil organic carbon, improve N and P use efficiency, and increase yields of rice–wheat system through inclusion of forage cowpea during the summer before cultivating the rice–wheat system. Cowpea forage harvested at 50 days removed greater amounts of N and P through aboveground biomass than those recycled through belowground roots and nodules. The NO₃-N in soil profile below 45 cm depth after wheat harvest was greater under fallow during summer than under cowpea, suggesting that cowpea minimized NO₃-N leaching beyond 45 cm depth. Similarly, in the treatments receiving both 120 kg N and 26 kg P ha⁻¹, NO₃-N in soil below 45 cm depth was lower compared to those receiving N or P alone. After three crop cycles, soil OC content in 0–15 and 15–30 cm depths was greater compared to initial OC in plots having cowpea. P applied at 26 kg ha⁻¹ increased available P content over initial P content, and also over P content of soil under no P treatments. The available P content was, however, invariably low under summer cowpea plots as compared to that under no cowpea ones. With continuous rice–wheat cropping, the bulk density (BD) of soil increased over the initial BD at different profile-depths, more so at 30–45 cm depth in no cowpea plots, but inclusion of summer cowpea helped decreasing the BD in the surface (0–15 cm) and sub-surface (15–30 and 30–45 cm) soil layers. Summer cowpea grown on residual fertility after wheat harvest did not influence rice yield, but increased wheat grain yield (P<0.05 during the terminal year), when both the crops received fertilizer N and P at recommended rates. Skipping of N or P or both, however, resulted in consistently low yield of these crops under summer cowpea treatments than those under no cowpea treatments, although the differences were not necessarily significant every year. The use efficiency of applied N and P fertilizers in rice and wheat, measured as agronomic efficiency and apparent recovery, was increased with the use of fertilizer N and P at recommended rates, and also with inclusion of summer cowpea.     

Allergenicity Assessment of Genetically-modified Tobacco Expressing Salt Tolerance cbl Gene

It is mandatory to assess the allergenic potential of genetically modified (GM) crops before their commercialization. Recently, a transgene [Calcineurin B-like (CBL) protein] has been introduced into tobacco plant to make the crop salt resistance. Therefore, it was felt necessary to assess the allergenic potential of the cbl gene product, which was introduced and expressed in Nicotiana tabacum (tobacco) plant and compared the allergenic effects with the wild-type (WT) counterpart. Bioinformatic analysis revealed that there was no significant sequence homology with known allergens. Also, no difference between the protein digestibility profiles of GM and WT tobacco was found. Rapid digestion of CBL protein (Mol Wt 35 kDa) by simulated gastric fluid (SGF) indicated reduced chances of this protein to induce allergenicity. In addition, BALB/c mice sensitized by intraperitoneal administration of WT and GM tobacco protein showed comparable levels of clinical score, specific IgE, IgG1, histamine level, similar effect on different organs as well as IgE binding proteins. These findings indicate that insertion of cbl gene in tobacco did not cause any additional allergic risk to consumer and the GM and native tobacco proteins behave similarly in both in vitro and in vivo situations even after genetic modification.     

Implications of genotype × input interactions in breeding superior genotypes for favorable and unfavorable rainfed upland environments

Resource-poor farmers in India cultivate upland rice as a subsistence crop in poor soil with minimum inputs, often applying little or no fertilizer and controlling weeds by hand. Consequently, upland rice yields are very low. In our study, the response to management intensification of fertilizer application at rates of 40 N ha⁻¹, 13 P ha⁻¹, and 16.7 K ha⁻¹ and two weed control treatments as compared with no fertilizer, and one hand weeding practice commonly followed by farmers in rainfed upland areas was examined with a large set of advanced breeding lines and adapted upland varieties tested over 3 years in multi-location trials. Highly significant genotype × environment interaction was observed in combined analyses across environments, leading to sub-grouping of sites into the high-yielding or favorable and low-yielding or unfavorable upland environment groups. A significant effect of management regime was observed. Averaged over 15 environments, the moderate-input treatment out-yielded the low-input treatment by nearly 65% or 0.8 t ha⁻¹ under favorable environments and by nearly 48% (0.3 t ha⁻¹) in unfavorable environments. A significant genotype effect and genotype × input management interaction for yield at favorable sites was observed. However, the same was not significant at unfavorable sites. Varietal differences were relatively small at unfavorable sites across input levels. The heritability estimates for grain yield were moderately high in both moderate- and low-input conditions in favorable environments. The genetic correlation between yields in moderate- and low-input conditions was high in both favorable and unfavorable environments. The study indicated that improved varieties performed well relative to landraces under low-input management. Improved varieties along with modestly intensified management offer an attractive option to increase the productivity of rainfed upland environments. For both favorable and unfavorable environments, indirect selection under moderate-input conditions was less efficient than direct selection for grain yield in low-input conditions, indicating upland breeding programs to adopt selection for grain yield under both moderate- and low-input conditions.     

Phenotypic diversity and identification of wild Arachis accessions with useful agronomic and nutritional traits

Wild relatives harbor novel sources of variation, which can be used to enhance the genetic base of a cultivar gene pool. A total of 269 accessions from 20 wild Arachis species belonging to six sections were evaluated for 41 morpho-agronomic traits and 89 selected accessions for oil, protein and total sugar content. Six plants from each accession were grown in an open Arachis house in large-cylindrical concrete structures during the 2004?C2005 season at Patancheru, India. REML analysis showed significant differences between species and accessions for most of the traits studied. Hierarchical cluster analysis, based on the first five principal component scores accounted for 82.5% variation, resulting in four clusters. Variation in genome relationships and ploidy levels had no bearing on the clustering pattern which was predominated by life forms: clusters 1 and 2, contained mostly annuals and clusters 3 and 4 perennials. A large range of variations were noticed among species for some of the agronomic traits: days to flowering, pod and seed characteristics, specific leaf area (SLA) and for SPAD chlorophyll meter reading (SCMR). Arachis duranensis showed the maximum intraspecific variation as revealed by a high diversity index for 23 of the 41 traits which included: days to flowering, primary branches, plant width, pod length, pod width, SCMR and SLA. The other species with desirable traits were A. pusilla (earliest flowering) and A. villosa (high SCMR at 60 and 80 days after sowing). The latter species is cross compatible with cultivated groundnut, thus, is a good source to enhance the trait value in the cultigen??s gene pool. The best 20 accessions with superior agronomic, nutritional quality and drought related trait combinations have been identified for their use in introgression of diverse and unique alleles from wild Arachis species into A. hypogaea.