A. K. Srivastva

Effect of fertilisation on carbon sequestration in soybean-wheat rotation under two contrasting soils and management practices in the Indian Himalayas.

We analysed results of a long-term experiments, initiated in 1973 on a sandy loam soil under rainfed condition and in 1995–96 on a silty clay loam soil under irrigated condition, to determine the influence of using different combinations of mineral fertiliser (NPK) and fertiliser + farmyard manure (FYM) at 10 Mg/ha on soil organic carbon (SOC) content and its changes in the 0–0.45 m soil depth. Fertilisation always caused a net gain in SOC stock. Such gain was positively proportional to the amount of C incorporated into the soils. Concentration of SOC in the 0–0.45 m depth increased by 44% in NPK + FYM treated plots compared with NPK (44.4 Mg C/ha) after 32 years under rainfed condition and by 14% in the NPK + FYM treated plots compared with NPK (41.76 Mg C/ha) after 9 years under irrigation. Mean (across treatments) total C added under the rainfed and irrigated systems was 2.67 and 3.03 Mg/ha.year, respectively. It was estimated that ~20 and 25% of the gross C input contributed towards the increase in SOC content under the rainfed and irrigated systems, respectively. Carbon loss from native soil organic matter (SOM) averaged ~61 and 261 kg C/ha.year under the rainfed and irrigated systems, respectively. Furthermore, mean stabilisation of added C in the plots under the rainfed condition (~16%) was higher than that (~13%) observed under the irrigated condition. Conversion of total added C to SOC was similar in the NPK and NPK + FYM treated plots under both growing conditions. In the NPK + FYM plots, ~38 and 29% of the C added through FYM was accounted for in the form of total SOC under the rainfed and irrigated conditions, respectively. The estimated quantity of biomass C required to maintain equilibrium SOM content under the rainfed and irrigated systems was 0.29 and 1.08 Mg/ha.year. The total annual C input by the soybean–wheat rotation in the unfertilised control plots under rainfed condition was 0.87 Mg/ha.year and with N fertiliser only under the irrigated condition was 1.75 Mg/ha.year. Thus, SOC augmentation under long-term soybean–wheat cropping was due to higher annual C input than the required amount to maintain equilibrium SOM content. Although FYM addition along with NPK improved total SOC stock and carbon sequestration potential, it did not encourage the stabilisation rate of added C. Hence, C stabilisation that takes into account the total C added in the system is a better indicator of assessing SOC sequestration. In summary, mineral fertilisation improved C sequestration capacity of soybean–wheat system in the Indian Himalayas and manure addition along with mineral fertilisers further improved it.

Soil properties and their relationships with crop productivity after 30 years of different fertilization in the Indian Himalayas

We analyzed results of a long-term (30 year) experiment under rainfed soybean-wheat rotation to determine the effects of differences in fertilization on selected soil properties and to investigate the relationship between these properties with crop yield. The results showed that addition of farmyard manure (FYM) with N or NPK fertilizers increased soil organic carbon (SOC) content. FYM application reduced bulk density. Mean weight diameter (MWD), plant available water capacity (PAWC) and water transmission characteristics of soil were highest in the NPK + FYM treatment and lowest in the unfertilized treatments, with the mineral fertilizer treatments showing intermediate results. Combined use of NPK and FYM increased total soil N, Olsen-P, exchangeable Ca2+ and exchangeable Mg2+ by ∼31, 13, 40 and 94%, respectively, in the 0–15 cm soil layer compared to application of NPK. Mean productivity of soybean-wheat system was positively correlated with total SOC stock, TSN stock, Ca2+, Mg2+, NH4OAc-K, MWD, PAWC, and dehydrogenase activity, and negatively related with soil bulk density. Thus, the changes in soil physical and biological properties should also be considered along with soil chemical properties/nutrient status to construe yield sustainability of other long-term field experimental data.

Yield potential of garden pea (Pisum sativum L.) varieties, and soil properties under organic and integrated nutrient management systems

The identification of suitable crop varieties that respond best to organic management is the key to achieving better crop yields. A field experiment was conducted during the winter season of 2005–2006 and 2006–2007 at Almora (Indian Himalayas) to evaluate the performance of five varieties of garden pea (Pisum sativum L.) and changes in the soil properties under organic and integrated nutrient management (INM) systems. The yield reduction under organic management was 14.4% in 2005–2006 and 10.1% in 2006–2007 compared with INM. Among the garden pea varieties ‘Vivek Matar 9’, ‘Vivek Matar 8’ and ‘Azad pea 1’ produced similar but significantly higher pod yield compared to other varieties. The soil pH, organic carbon, and microbial activities in terms of dehydrogenase and phosphatase (acid and alkaline) were higher in the plots under organic management compared to INM. The latter, however, had higher activity of urease, and N, P, and K contents in soil. We conclude that at least 15–20% price premium for organic garden pea may be required to offset the higher cost of cultivation and low yields under organic production system. Among the garden pea varieties, ‘Azad pea 1’, ‘Vivek Matar 8’ and ‘Vivek Matar 9’ were found suitable for organic cultivation.

Optimization of Farmyard Manure to Substitute Mineral Fertilizer for Sustainable Productivity and Higher Carbon Sequestration Potential and Profitability under Gardenpea-French Bean Cropping System in the Indian Himalayas

Carbon sequestration potential (CSP) and sustainability of gardenpea-french bean cropping system was assessed with farmyard manure (FYM) application vis-à-vis mineral fertilization as recommended NPK (NPK) and integrated nutrient management practices (INM) after six years’ cropping in Indian Himalayas. Application of 20 tons FYM ha−1 provided highest CSP (0.527 Mg C ha−1 year−1) in soil and sustainability index. With the help of quadratic equations, it was estimated that maximum profit (optimum yield) and turn over of invested money could be achieved with application of 20.0 and 15.6 t FYM ha−1, respectively. Application of 5.9 and 8.9 tons FYM ha−1 would substitute NPK and INM, respectively. Pod number plant−1 was the most important yield-contributing attribute as found from principal component analysis. Pod yield could be modelled through multiple linear equation with help of yield attributes.

Evaluation of mulching, stale seedbed, hand weeding and hoeing for weed control in organic garden pea (Pisum sativum sub sp. Hortens L.)

Weeds are often recognized as the principal biotic constraint to organic crop production. Development of suitable weed control measures is, therefore, a prerequisite for profitable organic farming. A field experiment was conducted during the winter season of 2003–2004 and 2004–2005 in the Indian Himalayas to evaluate the effect of mulching, stale seedbed, hand weeding and hoeing on weeds and yield of organic garden pea (Pisum sativum sub sp. Hortens L.). The weed population ranged from 249–477 m−2, and Polygonum plebejum L. (34%), Melilotus indica L. (31%) and Avena ludoviciana Dur. (17%) were the predominant weeds in the experimental field. Season long weed-crop competition reduced the green pod yield of garden pea by 74% in 2003–2004 and 93% in 2004–2005. All the weed control treatments significantly reduced the population and biomass of weeds resulting in significant increase in green pod yield of garden pea compared to unweeded control. The highest weed control efficiency (84% reduction in weed biomass) was achieved with hand weeding 30 and 60 days after sowing (DAS) closely followed by stale seedbed coupled with one hand weeding (77%). Both these treatments produced significantly higher green pod yield compared to other treatments in both the years. In 2003–2004, hand weeding (30 and 60 DAS) recorded the highest gross margin (Indian Rupees 115,400 ha−1) closely followed by stale seedbed coupled with one hand weeding (Indian Rupees 109,700 ha−1). In the second year, however, the latter treatment gave the highest gross margin (Indian Rupees 56,900 ha−1) compared to other treatments.

Performance of pigeon pea (Cajanus cajan L. Millsp.) at different sowing dates in the mid-hills of Indian Himalaya

Pigeon pea (Cajanus cajan L. Millsp.) is one of the most important tropical legumes in world. But its cultivation is limited to the hilly regions of India. A field experiment was conducted during kharif (wet) seasons of 2004 and 2005 to find out the optimum sowing time of pigeon pea in the mid-hills of north-west Himalaya. Significant difference in growth, yield attributes and yield were recorded due to different dates of sowing. Plant height, branches plant−1, grains plant−1 and grain weight plant−1 were affected due to late sowing on 20 June and 30 June, when compared to 20 May to 10 June sowing. Test weight decreased in 30 June sowing, under earlier sowing dates. Mean grain yield was highest in 30 May sowing (1.34 Mg ha−1) followed by 20 May sowing (1.30 Mg ha−1) whereas, it was only 0.66 Mg ha−1 under 30 June sowing. Harvest index under 20 May to 20 June sowing were on a par and significantly superior over 30 June sowing. Days to 50% flowering and heat unit required for 50% flowering were almost similar for 20 May to 10 June sowing and increased under 20 and 30 June sowing.