Soil organic carbon (SOC) content and its spatial distribution in the Northern Gangetic Plain (NGP) Zone of India were determined to establish the cause–effect relationship between agro‐ecological characteristics, prevailing crop management practices and SOC stock. Area Spread Index (ASI) approach was used to collect soil samples from the NGP areas supporting predominant cropping systems. Exponential ordinary kriging was found most suitable geo‐statistical model for developing SOC surface maps of the NGP. Predicted surface maps indicated that 43.7% area of NGP had 0.5–0.6% SOC, while the rest of the area was equally distributed with high (0.61–0.75%) and low (< 0.5%) SOC content levels. Averaged across cropping systems, maximum SOC content was recorded in Bhabar and Tarai Zone (BTZ), followed by Central Plain Zone (CPZ), Mid‐Western Plain Zone (MWPZ), Western Plain Zone (WPZ) and South‐Western Plain Zone (SWPZ) of the NGP. The SOC stock was above the optimum threshold (> 12.5 Mg/ha) in 97.8, 57.6 and 46.4% areas of BTZ, CPZ and MWPZ, respectively. Only 9.8 and 0.4% area of WPZ and SWPZ, respectively, had SOC stock above the threshold value. The variation in SOC stock was attributed largely to carbon addition through recycling of organic sources, cropping systems, tillage intensity, crop or residue cover and land‐use efficiency, nutrient‐use pattern, soil texture and prevailing ecosystem. Adoption of conservation agriculture, balanced use of nutrients, inclusion of legumes in cropping systems and agro‐forestry were suggested for enhancing SOC stock in the region.

Article InfoAn understanding of the dynamics of soil organic carbon (SOC) as affected by farming practices is imperative for maintaining soil productivity. The objective of this study was to assess the effect of tillage systems and inorganic inputs with K sap on the changes in SOC under rice -wheat rotation in western IGP. Results showed that ZT increased soil bulk density in the 0-20 cm soil layer. Adoption of ZT and PRB increased the concentrations of SOC and TC at 0-15 cm depth but decreased the concentrations in deeper soil. The greatest SOC and TC concentrations were observed under ZT at 0-15 cm depth and under PRB at 15-30 cm depth. Adoption of ZT farming enhanced the SOC and TC stocks in the 0-15 cm layer, whereas PRB increased SOC and TC stocks in the 15-30 cm profile. The stratification ratio (SR) of the SOC and TC concentrations was larger under ZT compared with PRB and CT. Thus, the adoption of short-term (5-6 years) ZT practices is beneficial for the enhancement of SOC and TC stocks in the 0-15 cm soil profile, and rotational tillage may be an appropriate farming practice for rice-wheat system. Application of NPK either through inorganic fertilizers or through combination of inorganic fertilizer and organics such as farm yard manure (FYM) with k sap improved the SOC, particulate organic carbon (POC), microbial biomass carbon (MBC) concentration and their sequestration rate. Application of 75% RDF +25% N through FYM with k sap in ricewheat rotation sequestered 0.39, 0.50, 0.51 and 0.62 Mg C ha −1 yr −1 over control, respectively. SOC with response to application of fertilizer partially substituted (25% on N basis) with organics was higher in 15% k sap. The rice water foot print recorded a significant declining trend in RDF plots where as the water foot print trend was stable at RDF+FYM plots and lower value under unfertilized control. The water productivity in RDF fertilized plots and RDF+FYM with k sap showed either an increasing trend or remained stable at all treatments during six years of the experiment.

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Biometrika Trust is collaborating with JSTOR to digitize, preserve and extend access to Biometrika. SUMMARY A family of sampling schemes with inclusion probability proportional to size is proposed. The schemes are based upon certain combinatorial properties of balanced incomplete block designs and are available for any sample size. Schemes belonging to this family are satisfactory from the point of view of (i) simplicity in selection, (ii) availability of an unbiased variance estimator and (iii) precision of the estimate. The efficiency has been compared empirically with that of some well-known sampling schemes.Some key words: Balanced incomplete block design; Doubly balanced design; Inclusion probability proportional to size sampling.