Ranjan Bhattacharyya

Long term effects of fertilization on carbon and nitrogen sequestration and aggregate associated carbon and nitrogen in the Indian sub-Himalayas

An understanding of the dynamics of soil organic carbon (SOC) as affected by farming practices is imperative for maintaining soil productivity and also for restraining global warming by CO2 evolution. Results of a long-term (30xa0year) experiment in the Indian Himalayas under rainfed soybean (Glycine max L.)—wheat (Triticum aestivum L.) rotation was analyzed to determine the influence of mineral fertilizer and farmyard manure (FYM) application at 10xa0Mgxa0ha−1 on SOC and total soil nitrogen (TSN) stocks and distribution within different aggregate size fractions. Fertilizers (NP, NK and NPK) and FYM in combination with N or NPK were applied before the soybean crop every year and no nutrient was applied before the wheat crop. Results showed that addition of FYM with N or NPK fertilizers increased SOC and TSN contents. The overall gain in SOC in the 0- to 45-cm soil depth interval in the plots under NPKxa0+xa0FYM treatment over NPK was 17.18xa0Mg Cxa0ha−1 in 30xa0year. The rate of conversion of input C to SOC was about 19% of each additional Mg C input per hectare. SOC content in large size aggregates was greater than in smaller size aggregates, and declined with decreased aggregate size. Thus, long-term soybean–wheat rotation in a sandy loam soil of the Indian Himalayas sequestered carbon and nitrogen. Soil organic C and TSN sequestration in the 0.25- to 0.1-mm size fraction is an ideal indicator of long-term C and N sequestration, since this fraction retained maximum SOC/TSN stock.

Long term fertilization effects on soil organic carbon pools in a sandy loam soil of the Indian sub-Himalayas

An understanding of the dynamics of soil organic carbon (SOC) as affected by farming practices is imperative for maintaining soil productivity and mitigating global warming. Results of a long-term (32xa0years) experiment in the Indian Himalayas under rainfed soybean (Glycine max L.)- wheat (Triticum aestivum L.) rotation was analyzed to determine the effects of mineral fertilizer and farmyard manure (FYM) application at 10xa0Mgu2009ha-1 on SOC stocks and depth distribution of the labile and recalcitrant pools of SOC. Results indicate all treatments increased SOC contents over the control. The annual application of NPK significantly (Pu2009<u20090.05) enhanced total SOC, oxidizable soil organic C and its fractions over the control plots. The increase in these SOC fractions was greater with the NPK + FYM treatment. Nearly 16% (mean of all treatments) of the estimated added C was stabilized into SOC both in the labile and recalcitrant pools, preferentially in the 0–30xa0cm soil layer. However, the labile:recalcitrant SOC ratios of applied C stabilized was largest in the 15–30xa0cm soil layer. About 62% of total SOC was present in the labile pool. Plots under the N + FYM and NPK + FYM treatments contained a larger proportion of total SOC in the recalcitrant pool than the plots with mineral or no fertilizer, indicating that FYM application promoted SOC stabilization.

Long-term yield trend and sustainability of rainfed soybean–wheat system through farmyard manure application in a sandy loam soil of the Indian Himalayas

A long-term (30xa0years) soybean–wheat experiment was conducted at Hawalbagh, Almora, India to study the effects of organic and inorganic sources of nutrients on grain yield trends of rainfed soybean (Glycinemax)–wheat (Triticumaestivum) system and nutrient status (soil C, N, P and K) in a sandy loam soil (Typic Haplaquept). The unfertilized plot supported 0.56xa0Mg ha−1 of soybean yield and 0.71xa0Mg ha−1 of wheat yield (average yield of 30xa0years). Soybean responded to inorganic NPK application and the yield increased significantly to 0.87xa0Mg ha−1 with NPK. Maximum yields of soybean (2.84xa0Mg ha−1) and residual wheat (1.88xa0Mg ha−1) were obtained in the plots under NPK + farmyard manure (FYM) treatment, which were significantly higher than yields observed under other treatments. Soybean yields in the plots under the unfertilized and the inorganic fertilizer treatments decreased with time, whereas yields increased significantly in the plots under N + FYM and NPK + FYM treatments. At the end of 30xa0years, total soil organic C (SOC) and total N concentrations increased in all the treatments. Soils under NPK + FYM-treated plots contained higher SOC and total N by 89 and 58% in the 0–45xa0cm soil layer, respectively, over that of the initial status. Hence, the decline in yields might be due to decline in available P and K status of soil. Combined use of NPK and FYM increased SOC, oxidizable SOC, total N, total P, Olsen P, and ammonium acetate exchangeable K by 37.8, 42.0, 20.8, 30.2, 25.0, and 52.7%, respectively, at 0–45xa0cm soil layer compared to application of NPK through inorganic fertilizers. However, the soil profiles under all the treatments had a net loss of nonexchangeable K, ranging from 172xa0kg ha−1 under treatment NK to a maximum of 960xa0kg ha−1 under NPK + FYM after 30xa0years of cropping. Depletion of available P and K might have contributed to the soybean yield decline in treatments where manure was not applied. The study also showed that although the combined NPK and FYM application sustained long-term productivity of the soybean–wheat system, increased K input is required to maintain soil nonexchangeable K level.

Expression of Soil Chemical and Biological Behavior on Nutritional Quality of Aromatic Rice as Influenced by Organic and Mineral Fertilization

The aim of the study was to evaluate changes in the yield and nutritional characteristics of aromatic rice as influenced by organic versus mineral fertilization. Aromatic rice was grown on four levels of cattle manure (CM; 5, 10, 15, and 20 Mg ha−1). Other treatments were equivalent amounts of nitrogen (N), phosphorus (P), and potassium (K) in different levels of manure fertilizer and mineral fertilizer. After 6 years of cropping, organically managed plots were superior to mineral-fertilized plots in terms of grain yields of rice at 5, 10, and 15 Mg ha−1. Cattle manure at 20 Mg ha−1 and its equivalent NPK through mineral-fertilizer treatment provided 41.1% and 37.9% increases in average grain yield (5.2 and 5.1 Mg ha−1) over the unamended control. Protein content was greater in mineral-fertilized rice grains at all levels of CM. Soil dehydrogenase, β-glucosidae, urease, and acid phosphatase activities were greater in soil treated with CM than soil treated with the corresponding mineral fertilizer at all levels. There was buildup of soil-available N, K, and iron (Fe) in soils treated with CM. Grain hardness increased with increasing rates of nutrient application for both mineral-fertilized and organically grown rice; in contrast, amylose content was lower in treatments receiving more nutrients, irrespective of nutrient sources. In terms of functional property, phenol content in rice grain increased with increasing nutrient supply. Potassium and Fe contents were more in CM-treated rice than in mineral-fertilized treatments at greater rates of application. Results suggest that after building up the soil nutrient status, comparable yield and better nutritional and functional qualities of rice can be achieved in organically managed soils than in mineral-fertilized soils.

Phosphorus dynamics and solubilizing microorganisms in acid soils under different land uses of Lesser Himalayas of India

Although chemical and some soil physical properties have been studied under different land uses of the Lesser Himalayas of India, very limited information is available on soil biochemical properties. Hence we investigated phosphorus (P) fractions [total P (TP), inorganic P (Pi), organic P (Po), available P, microbial biomass P (MBP)], enzyme activities [dehydrogenase, phosphatases, phytase], phosphate solubilizing bacteria (PSB) and fungi (PSF), and their correlations of acid soils (0–15 and 15–30xa0cm depths) under different land uses (viz, organic farming, maize–wheat, apple orchard, undisturbed oak forest and uncultivated land of the Indian Himalayas). All land use systems differed significantly for the P fractions, except TP. The highest values for TP, Pi, available P and MBP were found in soils under oak forest and lowest in uncultivated land. However, Po content was highest in apple orchard. The organic farming (organic manures field under garden pea-french bean cropping system forxa0>xa010xa0years) maintained highest activities of dehydrogenase, acid phosphatase and alkaline phosphatase. The highest phytase activity and highest numbers of PSB (99xa0×xa0103xa0g−1 soil) and PSF (30xa0×xa0103xa0g−1 soil) were observed in the rhizosphere soils of oak forest. Significant relationships between soil P fractions and enzyme activities, except alkaline phosphatase, were recorded in surface soil layer. PSB and PSF population were also correlated significantly with P fractions and enzyme activities. This would lead us to understand the level of degradation of P pools due to cultivation over forest system and the suitable management practices needed for soil quality restoration.