Typic Haplustert Research Articles

Interspecific Interaction and Nutrient Use in Soybean/Sorghum Intercropping System

Intercropping soybean (Glycine max L.) with sorghum (Sorghum bicolor L.) is common in the semiarid tropics of India. In most intercropping studies, little attention has been paid to belowground interaction and nutrient management other than N while assessing yield advantage. In a 5‐yr field experiment (2000–2004), we evaluated the impact of fertilizer and organic manures on below‐ and aboveground interaction, competitive ability, and economic viability of this intercropping at the Indian Institute of Soil Science, Bhopal for deep Vertisol (isohyperthermic Typic Haplustert) of central India. Above‐ and belowground growth components as well as biological activities were greatly improved in intercropped sorghum while the value of these except nitrate reductase (NR) activity, soil microbial biomass C (SMBC), and dehydrogenase activity (DHA) were reduced in intercropped soybean indicating interspecies competition between component crops. The increased NR activity, SMBC, and DHA in intercropped soybean revealed interspecies facilitation between the component crops. This showed that interspecies competition concurred with interspecies facilitation in this system. We observed that yield and land equivalent ratio (LER) of both the intercrops increased over sole crops though based on aggressivity and relative crowding coefficient (RCC), sorghum (+) is more competitive than soybean. Interaction of yield with different components indicated that three belowground components, i.e., NR activity in root (r = 0.62, r = 0.63, P < 0.05), root length density (r = 0.36, r = 0.33, P < 0.05), and SMBC (r = 0.71, r = 0.66, P < 0.05) of both intercrop soybean and intercrop sorghum, respectively, had the greater effect on yield advantage in the intercropping system. Soybean did not benefit from intercropping to the same degree as sorghum under N–P–K. Nutrient application influenced LER, RCC, and monetary advantage index and was found in the order of N–P–K plus farmyard manure (FYM) > N–P–K plus poultry manure (PM) > N–P–K plus phosphocompost (PC) > N–P–K > control. However, based on competition ratio, yield advantage was greater under N–P–K plus PM. The results suggest that sorghum is the major contributor to the mixture yield and that the integrated use of N–P–K plus FYM or N–P–K plus PM is an important nutrient management option for sustaining this intercropping system, particularly to benefit the legume component.

Morphology, physico-chemical properties and classification of some vertisols of Jabalpur

Three Vertisol pedons in Jabalpur district, were morphologically studied, characterized and classified. The soils are very deep, colour ranges from dark brown (10YR3/1) to very dark grey (10YR4/3) in different horizons. The texture of deep soils clay of all pedons throughout the profile. Crack of 2-3 cm wide extends beyond one meter. Slickensides, wedge shaped aggreagates, Fe, Mn and calcrets are observed in all the soils pedons. The soil are imperfectly drained. The soils are calcareous and PH ranged form neutral to mildy alkaline. The organic carbon content in these soils were low to medium in surface and that too decreased with depth. Effervescence was observed in all the soils pedons in lower horizons. The soils are base rich and high in CEC : clay ratio (0.60 to 0.93) and are classifed as Typic Haplusterts.

Carbon sequestration potential and sustainable yield index for groundnut- and fallow-based cropping systems

Soil organic carbon storage encompasses both soil productivity and environmental capabilities. The influence of fertilizer (nitrogen and phosphorus) levels (0 NP, 0·5 NP, 1·0 NP (recommended standard) or 1·5 NP) on total system productivity, sustainable yield index and soil organic carbon storage in Vertisols (Typic Haplustert) under groundnut and fallow-based cropping systems were examined in a field experiment over 6 years. The aim was to identify a system that provided an acceptable balance between total system productivity and soil organic carbon restoration. The experiment comprised two rainy season crops (groundnut or fallow) and five post-rainy season crops (wheat, mustard, chickpea, sunflower or summer groundnut), each post-rainy season crop with four levels of NP fertilizer. The total system productivity was 130% higher in the groundnut-based than in the fallow-based system and was in the order: groundnut–groundnut>groundnut–chickpea>groundnut–wheat>groundnut–mustard>groundnut–sunflower. The sustainable yield index was highest in the groundnut–groundnut system. The gross C input was relatively higher in the groundnut-based system but the C loss rate was greater. The amount of residue needed per ha per year to compensate for loss of soil organic carbon was estimated to be 4·3 t in the fallow-based and 7·6 t in the groundnut–based cropping system. Though the total system productivity was greater in groundnut–groundnut and groundnut–chickpea systems, soil organic carbon declined. The groundnut–wheat system contributed more C, particularly root biomass C, than other systems, improved the restoration of soil organic carbon and maintained total system productivity. It was concluded that current fertilizer recommendations are adequate for maintaining yields in groundnut-based systems but the addition of crop residues at regular intervals along with fertilizer is necessary to maintain restoration of soil organic carbon.

Uptake of major nutrients in above ground parts of promising mid late maturing sugarcane clones

Ten mid late maturing promising sugarcane clones including three standards were evaluated for major nutrient uptake and use efficiency in ratoon crop grown in a clay soil (Typic Haplustert). Concentration of N, P and K in dry leaves, green tops and stem were determined and their uptake in the individual plant parts, total above ground parts and uptake of nutrients (kg) per tonne of cane produced were computed. Clones differed significantly in N, P and K uptake in dry leaves, green tops, stem and total above ground parts and kg nutrients to produce a tonne of cane. Total N uptake ranged from 50.19 kg/ha in Co 7219 to 84.24 kg/ha in Co 93014. The lowest uptake of N per tonne of cane was 0.812 kg in Co 93009 and the highest was 1.135 kg in Co 93016. Total P uptake varied from 16.09 kg/ha in Co 7219 to 32.01 kg/ha in Co 93009. Uptake of P per tonne of cane varied from 0.297 kg in Co 86032 to 0.449 kg in Co 93016. Total K uptake ranged form 94.80 kg/ha in Co 93010 to 240.03 kg/ha in Co 6304. The lowest and the highest K uptake to produce a tonne of cane were 1.50 kg in Co 93010 and 3.10 kg in Co 6304 respectively. Clones CoG 93076, Co 93010 and Co 93009 were identified for better NPK use efficiency.

Long-term effect of fertilizer and manure application on soil organic carbon storage, soil quality and yield sustainability under sub-humid and semi-arid tropical India

In south Asian countries, production fatigue has been observed as yields which have started declining or stagnating under long-term experiments in multiple cropping systems due to continuous cultivation. We examined the potential impact of continuous cultivation of crops in rotation, and fertilizer and manure application on yield trends, soil organic carbon (SOC) storage, soil quality parameters (active fractions of SOC in particular) and sustainable yield index (SYI). Crop rotations included in the study were: rice–wheat–jute, soybean–wheat and sorghum–wheat system at Barrackpore (Typic Eutrochrept), Ranchi (Typic Haplustalf) and Akola (Typic Haplustert), respectively. Field treatments included unfertilized (control), 100% N, 100% NP, 100% NPK and 100% NPK + FYM. The negative yield trend was observed in unbalanced use of inorganic N and NP application at all the three sites. The positive yield trend was observed in the NPK and NPK + FYM treatments at Ranchi and Akola. However, significantly negative-yield trends were observed in these treatments at Barrackpore under rice-based system. Results showed that the SOC in the unfertilized plot (control) decreased by 41.5, 24.5, and 15.5% compared to initial values in Barrackpore, Ranchi and Akola, respectively, wherein the treatment receiving NPK and NPK + FYM either maintained or improved it over initial SOC content in these sites. The estimated annual C input values in NPK + FYM treatments were 4392, 4159 and 3113 kg ha −1 year −1 in rice–wheat–jute, sorghum–wheat and soybean–wheat system, respectively. Active fractions of SOC, viz., water-soluble carbon and hydrolysable carbohydrates, soil microbial biomass C and N, dehydrogenase and alkaline phosphatase activity, improved significantly with the application of NPK and NPK + FYM. The content of SOC significantly ( p ≤ 0.05) correlated with SYI and active fractions of SOC, which support better sustainable productivity. Results suggest that current fertilizer recommendations of 100% recommended NPK are adequate for maintaining SOC and its active fractions as well. The causes of yield decline are mostly location specific but depletion of SOC and its active fractions seems to be a general cause.

Suitability of cotton cultivation in shrink–swell soils in central India

Rainfed cotton farming is a risky enterprise. It has always been a challenge to sustain cotton productivity under rainfed conditions not only in India but also in similar agro-environments elsewhere. The present study is an attempt to find out the most sustainable soil under varying rainfall through crop yield correlation with agro-environment factors, like soil physiographic conditions, growing period rainfall, crop ET and phasic rainfall, by conducting (farmers’) field experiment in a representative catena with four different soil types in central India. Cotton (hybrid-H4) was grown for 5 years; 3 years under normal rainfall, 1 year under excessive rainfall and 1 year under drought conditions. The investigation revealed that in the excess rainfall to drought years, yield fluctuation varied from 2% to 38% over the normal year in shallow soils occurring on a pediment plain to the very deep soils in a valley plain. However, the yield fluctuation in deep Vertisols occurring on lower Piedmont and narrow valley, representing Vertic Haplustepts (P3) and Typic Haplusterts (P4), was 25–38% and 6–25%, respectively. The low yield fluctuation and high yield correlation with agro-environmental factors, observed for P3 soils, suggests the suitability of Vertic Haplustepts (P3) for cotton production under varying rainfall conditions. Cultivating P3 soils for cotton could stabilize the income of cotton farmers and research relating to cotton genotype improvement under rainfed conditions should be carried out to minimize soil effects. The international land evaluation criteria suggested by FAO show that Vertisols (P3 and P4) qualify as a suitable category for cotton production under rainfed conditions. However, the present study indicates that this categorization may need revision in view of the adverse climatic conditions of central India. In order to improve the effectiveness of the FAO’s land evaluation criteria for sub-tropical Vertisols, the study suggests that more emphasis be given to rainfall in the critical growth phases related to crop yield and to soil hydraulic conductivity related to the Ca 2+/Mg 2+ ratio in computing land indices, rather than total quantum rainfall during the growing period. Also, too many soil properties are presently considered in the FAO method. A quantum of 250–325 mm rainfall at the square initiation to peak flowering stages was found to influence yield. Under climatic aberration, the high fluctuation of cotton productivity in deep Vertisol (P4) may be minimized by adoption of any soil management technology (e.g. ridges or broad-bed furrow system) that helps in improving internal drainage. It is, therefore, urgent that the Indian Government should enact special legislation or introduce incentives for the Vertisol farmers who mostly use old cultivation practices to adopt such technology on a large scale. A quadratic regression model developed in this study to compute the yield under varying rainfall may help in estimating the economic losses to the farmers and quantifying crop insurance compensation.

Eficiencia de un acondicionador de suelo en la producción de maíz dulce en el Valle de Lajas

El rendimiento de los cultivos en regiones semiáridas puede aumentarse mejorando el contenido hídrico en el suelo o el uso de acondicionadores de suelo. Barbary-Plante (BP) es un acondicionador comercial de suelo que consiste de un polímero de acrilamida de sodio que contiene macro- y m¡cronutrimentos, entre otros componentes. El fabricante alega que este producto mejora la disponibilidad de nutrimentos, retensión de agua y la estabilidad de agregados en el suelo. La eficacia de BP como acondicionador de suelo se probó en maíz dulce (Zea mays L. cv. Sure Sweet) en la región semiárida del suroeste de Puerto Rico (Valle de Lajas). El suelo en el predio experimental pertenece a la serie Fraternidad (fino, esmectítico, isohipertérmico Typic Haplusterts). La serie Fraternidad es un Vertisol, orden de suelo más predominante en el Valle de Lajas. El maíz dulce se sembró el 20 de febrero de 2001 a una densidad de 64,000 plantas por hectárea. Los tratamientos probados fueron 0, 50 y 100 kg/ha de BP sin hidratar y riego por goteo a razón de 0,50 y 100% de reposición de evapotranspiración. Los tratamientos de riego por goteo se programaron utilizando el método del tanque de evaporación. Una vez hidratado, según la recomendación del fabricante, el BP se incorporó al suelo al momento de la siembra. Los tratamientos de BP se suplementaron con fertilizantes inorgánicos hasta alcanzar un nivel de 150-50-150 kg/ha de N-P205-K20. Los niveles de riego afectaron el rendimiento de mazorcas comerciales. En cambio, las aplicaciones de BP no afectaron el rendimiento de mazorcas comerciales. Aplicaciones de 50 kg/ha de BP produjeron la mayor germinación, aunque no significativamente mayor que en las parcelas no tratadas. En términos generales el efecto de BP en la germinación del maíz dulce fue inconsistente.

Quantification of N2 fixation and annual N benefit from N2 fixation in soybean accrued to the soil under soybean‐wheat continuous rotation

AbstractA computational exercise was undertaken to quantify the percent N derived from atmosphere %Ndfa) in soybean and consequent N benefit from biological N2‐fixation process annually accrued to the soil by the soybean crop using average annual N‐input/‐output balance sheet from a 7 yr old soybean‐wheat continuous rotational experiment on a Typic Haplustert. The experiment was conducted with 16 treatments comprised of combinations of four annual rates of farmyard manure (FYM ≅ 0, 4, 8, and 16 t ha–1) and four annual rates of fertilizer N (≅ 0, 72.5, 145, and 230 kg N ha–1) applications. The estimated N contributed through residual biomass of soybean (RBNS) consisting of leaf fall, root, nodules, and rhizodeposition varied in the ranges of 7.02–16.94, 11.65–28.83, 3.31–8.91, and 11.3–23.8 kg N ha–1 yr–1, respectively. A linear relationship was observed between RBNS and harvested biomass N (HBNS) of soybean in the form of RBNS = 0.461 × HBNS – 20.67 (r = 0.989, P < 0.01), indicating that for each 100 kg N assimilated by the harvested biomass of soybean, 25.4 kg N was added to the soil through residual biomass. The Ndfa values ranged between 13% and 81% depending upon the annual rates of application of fertilizer N and FYM. As per the main effects, the %Ndfa declined from 76.4 to 26.0 with the increase in annual fertilizer‐N application from 0 to 230 kg N ha–1, whereas %Ndfa increased from 40.8 to 65.8 with the increase in FYM rates from 0 to 16 t ha–1, respectively. The N benefit from biological N2 fixation accrued to the soil through residual biomass of soybean ranged from 7.6 to 53.7 kg N ha–1 yr–1. The treatments having %Ndfa values higher than 78 showed considerable annual contribution of N from N2 fixation to the soil which were sufficient enough to offset the quantity of N removed from the soil (i.e., native soil N / FYM‐N / fertilizer‐N) with harvested biomass of soybean.

Evaluation of early maturing promising sugarcane clones for nutrient use efficiency

A field experiment was conducted to evaluate promising sugarcane clones for nutrient use efficiency. Twelve early maturing sugarcane clones including two standards were planted in a clay soil (Typic Haplustert). Dried plant materials were analysed for nitrogen, phosphorus and potassium content in dry leaves, green tops and stem. Total uptake of nutrients in above ground parts was determined. Total N uptake ranged from 66.30 kg/ha in Co 93003 to 43.30kg/ha in Co 85004 with a mean of 109.66 kg/ha. The lowest uptake of N per tonne of cane was recorded by Co 94005 (0.76 kg) and the highest was in Co 94004 (1.40 kg). Clones Co 94005, Co 93003 and Co 94008 showed better utilization of nitrogen. The lowest total uptake of phosphorus by above ground parts (24.91 kg/ha) was observed in Co 93001, while the highest was observed in CoC. 671 (59.98 kg/ha). The variation of kg P per tonne of cane was from 0.285 in Co 93001 to 0.585 in Co 94002. Clones Co 93001, Co 94005, Co 93003 and Co 94003 removed relatively lower quantity of phosphorus for producing a tonne of cane. With regard to potassium, Co 85004 recorded the highest K uptake of 293.61 kg/ha and the lowest of 87.91 kg was registered in Co 94003. Clone showing the lowest K uptake to produce a tonne of cane (1.09 kg) was Co 94003 and the highest was Co 85004 (2.75 kg). Clones Co 94003, Co 93003, Co 93001 and Co 94005 removed comparatively lower amounts of potassium to produce a tonne of cane. Clones Co 93003 and Co 94005 were found to be more efficient in utilization of NPK nutrients. i.e. produce more tonnage of cane per unit quantity of nutrients taken up.

Unsaturated flow of different quality irrigation waters through clay, clay loam and silt loam soils and its dependence on soil and solution parameters

The effect of total electrolyte concentration (TEC) and sodium adsorption ratio (SAR) of irrigation water on unsaturated hydraulic properties, viz. unsaturated hydraulic conductivity, wetting front advancement and soil-water diffusivity of clay (Typic Haplustert), clay loam (Vertic Haplustept) and silt loam (Lithic Haplorthent) soil was studied in a laboratory experiment. Twenty-four types of irrigation waters, encompassing four TEC levels, viz. 5, 10, 20 and 50 me l −1 and six SAR levels, viz. 2.5, 5, 10, 15, 20 and 30 m mol 1/2 l −1/2 were synthesised to equilibrate the soil samples using pure chloride salts of calcium, magnesium and sodium at Mg:Ca=1:2. Unsaturated hydraulic conductivity ( K θ ), was determined both directly (by ‘inflow–outflow’ vertical infiltration method for water potentials of −5 and −10 kPa) and indirectly (from diffusivity functions and soil-water retention curves) in two different water potential ranges. Wetting front advancement and diffusivity ( D θ ) were determined by the horizontal infiltration method. Water quality had larger impacts on the unsaturated hydraulic conductivities of the silt loam soil than on the clay and clay loam soils. The effects of TEC and SAR were both large for the silt loam soil whereas the effects of SAR were predominant for the clay and clay loam soils. At a water potential of −5 kPa (50 cm suction), the hydraulic conductivity of clay and clay loam soils was approximately 10 times smaller than at saturation under different quality waters. However, the hydraulic conductivity of silt loam soil was approximately 10 and 100 times smaller than at saturation for low SAR (up to 10 m mol 1/2 l −1/2) and high SAR (15 m mol 1/2 l −1/2 and above) waters, respectively. Influence of irrigation water quality on K θ increased with decreasing water content. SAR of water and exchangeable sodium percentage (ESP) of soils influenced K θ significantly. Besides SAR, TEC also influenced K θ of silt loam significantly. D θ increased with increase in TEC and/or decrease in SAR of water. The clay soil was found to be the most sensitive soil to unsaturated flow above SAR 15 m mol 1/2 l −1/2. At higher and lower water contents, the dependence of D θ on SAR of water and ESP of soil was found to be highly significant. However, in silt loam soil it was significantly dependent on TEC of water also.

Sorption and distribution of adsorbed metals in three soils of India

The mobility and bioavailability of heavy metals depends on the metal retention capacity of soil and also on the geochemical phases with which metals are associated. Laboratory batch experiments were carried out to study the sorption and distribution of Cd, Ni and Pb in 3 soils differing in their physicochemical properties from India: Oxyaquic Haplustalf (SL1), Typic Haplustalf (SL2) and Typic Haplustert (SL3). The heavy metal adsorption was studied by isotherms and the distribution coefficient ( K D) for each metal was obtained from the linear regressions of the concentration of metal remaining in equilibrium solution and the amount adsorbed. In general, the sorption capacity for all the metals decreased in the order: SL3>SL2>SL1. Among metals, the sorption capacity in all the soils decreased in the order: Pb>>Ni>Cd. Distribution of sorbed metals at various equilibrating concentrations was studied by sequential extraction. Results showed significant differences in the distribution of metals in these soils. At higher additions (such as 200 μM l −1) most of the metals were extracted in their more mobile fractions, exchangeable and/or inorganic in contrast to their original partitioning in soils, where they were preferentially associated with the less mobile residual fraction. Largest percentages of metals extracted in the exchangeable fraction corresponded to those soil–metal systems with smaller K D values, e.g. Cd, Ni and Pb in SL1 and Cd and Ni in SL2. In neutral and alkaline soils (SL2, pH=7.1, and SL3, pH=8.6) Pb was predominantly extracted from the inorganic fractions and this corresponded to higher K D values for Pb in these soils. The predominance of metals associated with the exchangeable fraction together with low K D values indicates higher mobility of metals retained in the acidic soil (SL1, pH=5.2) compared with the others.

The availability of potassium in Aeric Haplaquept and Typic Haplustert as affected by long-term cropping, fertilization and manuring

The effect of long-term cropping, fertilization and manuring after 21years of rice-rice cropping on an Aeric Haplaquept and after 27years of soybean-wheat system on Typic Haplustert on the availability ofpotassium (K) using a Quantity-Intensity (Q/I) relationship was investigated atBhubaneswar and Jabalpur, respectively in India. Q/I relationships of potassiumprovide general information on the nature of K equilibrium and serve as a goodindex of K supplying power of soil. The treatments selected for the study were:control (no fertilizer), nitrogen (N), nitrogen + phosphorus(NP), nitrogen + phosphorus + potassium(NPK) and NPK + farmyard manure (FYM). Nutrients N, P and Kwere applied at 200 kg N/ha, 52 kg P/ha and 100kg K/ha in Aeric Haplaquept to the rice-rice system and220 kg N/ha, 96 kg P/ha and 77 kg K/hainTypic Haplustert to the soybean-wheat system. Farmyard manure was applied everyyear only to Kharif (wet season) rice at 10t/ha (Aeric Haplaquept) and 15 t/ha to soybean crop(Typic Haplustert). In both soils the values of equilibrium activity ratio (AReK), the activity ratio of K in soil solution inequilibrium with the soil, non-specific or immediate available K and K onspecific sites or difficultly available K were observed in the following order:NPK + FYM > NPK > control > N > NP.The magnitude of AReK < 0.001 (moll−1)1/2 showed that the K adsorption at edgepositions was predominant in NP plots in the Typic Haplustert and in control, Nand NP plots in the Aeric Haplaquept. The ΔK0 became morenegative in the NPK and NPK + FYM treated plots, therebyindicating a greater K release into the soil solution. The potential bufferingcapacity, a measure of the ability of the soil to maintain the intensity of Kinthe soil solution was low in both the soils, irrespective of fertilizertreatments and indicated poor K release and low K supplying capacity of thesoils. Free energies of exchange (ΔG) for the replacement of calcium withpotassium ranged from −5348 to −3379 cal M−1 K−1 and were associatedwithpotassium deficiencies in plants in both the soils. The Aeric Haplaquept hadvery low values of exchangeable + water soluble K,AReK, KL and ΔG, thereby indicating a Kstress environment. The maximum and minimum contribution of non-exchangeable Kto plant uptake were found for NP and NPK + FYM plots,respectively. The results suggest that continuous cropping without K inputscaused a greater decline in K supplying power of the soil and emphasise theneedfor balanced and integrated use of organic and K inputs regularly to sustain asteady supply of K to successive crops.

Effect of water quality on exchange phase — solution phase behavior of three soils

The effect of total electrolyte concentration (TEC) and sodium adsorption ratio (SAR) of water on ESR-SAR relationships of clay (Typic Haplustert), clay loam (Vertic Haplustept) and silt loam (Lithic Haplorthent) soils was studied in a laboratory experiment. Twenty four solutions, encompassing four TEC levels viz., 5, 10, 20, and 50 mmolc l—1 and six SAR levels viz., 2.5, 5, 10, 15, 20, and 30 mmol1/2l—1/2 were synthesized to equilibrate the soil samples using pure chloride salts of calcium, magnesium, and sodium at Mg:Ca = 1:2. SAR of equilibrium solution decreased as compared to the equilibrating solution and more so in waters of low salt concentration and high SAR. At low electrolyte concentration, high SAR values were not attained in the equilibrium solution because of addition of calcium and magnesium from the mineral dissolution and from the exchange phase. Irrespective of TEC, exchangeable sodium in all the soils increased by about 4.5 to 5-fold and irrespective of SAR, it increased by about 1.4- to 1.8-fold. A positive interaction of TEC and SAR influenced the ESP build-up and CEC played a major role in the visual disparity in sodication of these soils. At higher TEC levels, considerable increase in ESP was observed when it was corrected for anion exclusion and more so in silt loam followed by clay loam and clay soils. The values for Gapons' constant were in the range 0.0110—0.0176, 0.0142—0.0246, and 0.0189—0.0344 mmol—1/2l1/2 in clay, clay loam, and silt loam soils, respectively. Increase in TEC from 5 to 50 mmolc l—1 resulted in 5.84, 8.33, and 9.77 % decrease in Gapons' constant of clay, clay loam, and silt loam soils, respectively. The soils exhibited differential affinity for Ca2+, Mg2+ or Na+ under different quality waters. Regression coefficients of ESR-SAR relationship were lower for low TEC as compared with high TEC waters. The exchange equilibrium was strongly affected by TEC of the solution phase. Variation in soil pH was gradual with respect to TEC and SAR of equilibrating solution and no sharp change was observed. Soluble salt concentration was doubled upon equilibration with low salt waters at all SAR levels in all the soils. However, the salt concentration remained unchanged upon equilibration with high salt waters. Considering pH 8.5 a boundary between soil salinity and sodicity, ESP values attained at TEC 5 mmolc l—1 were 7.34, 8.02, and 14.32 for clay, clay loam, and silt loam soils, respectively.

Potassium balance and release kinetics of non-exchangeable K in a Typic Haplustert as influenced by cattle manure application under a soybean-wheat system

Potassium balance and non-exchangeable potassium release in 0.01 M CaCl2 medium in a Typic Haplustert were studied in a 7-year-old soybean–wheat rotational experiment involving 4 levels of cattle manure along with the recommended dose of K (66 kg/ha.year). Continuous cropping without returning crop residues to the soil led to a negative balance of 66–107 kg K/ha.year. Manuring at the rate of 4 and 8 t/ha did not significantly change the negative balance, but application of 16 t/ha manure reduced the negative K balance. Continuous cropping without cattle manure reduced cumulative K release from 236 mg/kg (initial) to 195 mg/kg. Application of manure at 4, 8, and 16 t/ha kept K release at 229, 245, and 246 mg/kg soil, respectively. A parabolic diffusion equation was the best fit to describe K release. Cropping under the present level of K input resulted in a decline in non-exchangeable K whatever the addition of manure. Manuring at 4 and 8 t/ha has accelerated the mining of native K, which increased the unsustainability of the system. K balance, non-exchangeable K release kinetics, soybean–wheat rotation, cattle manure, Typic Haplustert.

Potassium balance and release kinetics under continuous rice–wheat cropping system in Vertisol

In an experiment conducted over 8 years at the research farm of the National Research Centre for Weed Sciences, Jabalpur, we investigated the effects of mineral fertilizer and organic manures on K balances and non-exchangeable K release kinetics in a Typic Haplustert under a rain-fed rice ( Oryza sativa L.) and irrigated wheat ( Triticum vulgare L.) system. Each year, rice was grown with variable levels of fertilizer N with and without organic manures, while recommended rates of 26 kg P ha −1 and 33 kg K ha −1 were applied to both the crops. Wheat was grown without organic manure but with the same levels of fertilizer N as for rice. The apparent K balance was measured as the difference between total K added and that removed by the crop. Increasing levels of fertilizer N resulted in an increase in the negative K balance from 56 kg ha −1 yr −1 (control) to 103 kg ha −1 yr −1 at 90 kg N ha −1 and 156 kg ha −1 at 180 kg N ha −1. Incorporation of farmyard manure (FYM) or green manure (GM) with fertilizer N reduced the negative K balance. Repeated extraction of soil with 0.01 M CaCl 2 revealed that continuous cropping for 8 years either without fertilizer N (control) or with 90 kg N ha −1 reduced the cumulative K release. However, the application of 180 kg ha −1 of fertilizer N not only maintained the cumulative K release but also improved it. Incorporation of 5 t FYM or 6 t GM ha −1 with 90 kg N ha −1 resulted in an increase in K release by 58 and 37 mg kg −1 soil, respectively, over the values measured in a soil sample collected at the onset of the experiment. A parabolic diffusion equation described the release rate of the non-exchangeable K. The equation suggested that the application of fertilizer N reduced the release rate of K, whereas the incorporation of manure, with fertilizers, increased it over the values obtained from soil collected at the onset of the experiment. The large cumulative K release at 180 kg N ha −1 was due to the amount of K released initially. Continuous cropping at a fertilizer level of 33 kg K ha −1 may pose a threat to the sustainability of the rice–wheat system. Recycling of crop residue or application of higher levels of fertilizer K may provide long-term sustainability to the system.

Relationship between C addition and storage in a Vertisol under soybean-wheat cropping system in sub-tropical central India

Kinetic relationship between addition of organic carbon (through unharvested crop biomass and externally applied farmyard manure) and storage in a Vertisol (Typic Haplustert) was studied in a seven-year soybean-wheat rotation experiment. We investigated 16 treatments comprised of combinations of four annual rates of farmyard manure (0, 4, 8 and 16 t ha—1 on dry weight basis) and four annual rates of fertilizer N (0, 72.5, 145, and 230 kg N ha—1). Average annual contribution of C input from soybean was 21.65% and from wheat was 32.32% of the harvestable above ground biomass. Net increases in the contents of soil organic C (Corg) at 0—15 and 15—30 cm depth were observed in all treatments. The annual rate of Corg enrichments ranged from 85 to 739 kg C ha—1 at 0—15 cm and 54 to 149 kg C ha—1 at 15—30 cm soil depth. The observed annual rate of change in Corg (δCs/δt, kg C ha—1 yr—1) at 0-30 cm was positively correlated with the gross annual C input (A, kg C ha—1 yr—1) to the 0—30 cm soil horizon, as described by a linear equation (δCs/δt = 0.1806 × A — 160.34; r = 0.978, P < 0.01). This indicates that 18.06% of the annual gross C input was incorporated in soil organic matter.

Saturated hydraulic conductivity, dispersion, swelling, and exchangeable sodium percentage of different textured soils as influenced by water quality

Effects of water quality on saturated hydraulic conductivity, dispersion, swelling, and exchangeable sodium build-up in clay (Typic Haplustert), clay loam (Vertic Haplustept) and silt loam (Lithic Ustorthent) soils were studied. Soil samples were equilibrated with twenty-four water quality combinations encompassing four total electrolyte concentrations (TEC) from 5 to 50 me L−1; and six sodium adsorption ratios (SAR) ranging between 2.5 and 30 m mol1/2L−1/2. Saturated hydraulic conductivity ranged from 0.009 to 0.157, 0.016 to 0.235; and 0.453 to 22.76 cm h−1, dispersion index from 11.6 to 26.0, 8.3 to 24.9; and 5.7 to 13.2%, coefficient of linear extensibility from 0.05 to 0.21, 0.03 to 0.14; and 0.007 to 0.032; and exchangeable sodium percentage (ESP) from 2.23 to 20.0, 3.18 to 24.55; and 4.26 to 32.4 for clay, clay loam, and silt loam soils, respectively. Dependence of saturated hydraulic conductivity on water quality parameters (TEC and SAR) and soil properties (dispersion, swelling and exchangeable sodium) was also studied. Clay and clay loam soils were equally sensitive to the changes in SAR and TEC of equilibrating solution, while silt loam found to be sensitive to the changes in TEC only. Multiple regression equations indicated the significant dependence of saturated hydraulic conductivity on ESP in all the soils. Dispersion and swelling found to be the important processes governing the changes in saturated hydraulic conductivity of clay and clay loam. However, changes in saturated hydraulic conductivity were mainly governed by dispersion in silt loam soil.

Crop residue addition effects on myriad forms and sorption of phosphorus in a Vertisol

Crop residues are a vital organic resource and their extensive use in soil management for sustainable agriculture is widely advocated. The effects of soybean residue (SR) and wheat residue (WR) applied alone or in combination with fertilizer P (FP) on dynamics of labile P, distribution of P fractions and P sorption in a Vertisol (Typic Haplustert) were assessed in a 16 week long incubation study. The amount of P added through crop residues, FP or their combination was kept constant at 10 mg P kg −1 soil. Addition of SR or WR resulted in net increase of labile inorganic (P i) and organic ( P o ) P , and microbial P throughout the incubation period, except that the WR decreased labile P i during the first two weeks due to P i immobilization. Integration of FP with SR had no added benefit compared to SR alone, while use of FP+WR proved better in ensuring short-term P availability by offsetting initial P immobilization associated with WR alone. Sequential fractionation of soil P at the end of 16 weeks showed that addition of SR and WR alone or in combination with FP favoured a build-up in labile P i and P o (NaHCO 3–P i and –P o), and moderately labile P o (NaOH–P o) fractions at the expense of recalcitrant P (HCl–P). The P sorption capacity of soil and P required to maintain optimum solution P concentration of 0.2 mg P l −1 also decreased with addition of these crop residues. The implication of the results of this study is that soybean and wheat residues can potentially improve soil P fertility by increasing labile P i and P o, and moderately labile P o fractions, decreasing P sorption and concomitantly causing dissolution of recalcitrant P in soil.

EVALUATING PLASTIC LIMIT IN VERTISOLS WITH A DROP-CONE PENETROMETER

The traditional thread and modified drop-cone penetrometer methods were used to evaluate the plastic limit of Vertisols (Typic Haplusterts). Quicker and more consistent results were obtained by a less experienced operator with the drop-cone penetrometer method, whereas the thread method required more time and an experienced operator. The plastic limits obtained with the thread method were lower than those obtained with the drop-cone penetrometer. Consistent results were obtained with the drop-cone penetrometer method by eliminating remolding of soils. This was done by using eight 30 mL plastic cups to which varying amounts of water had been added. Soil was then added to the cups. The soil water content (g 100g−1) was obtained from the top 10 mm of soil in each plastic cup. This depth was chosen as it was found to be the maximum depth to which the cone penetrated. It also eliminated the problem of a moisture gradient in the plastic cups.

Changes in organic and inorganic sulfur fractions and S mineralisation in a Typic Haplustert after long-term cropping with different fertiliser and organic manure inputs

Changes in the status of organic and inorganic pools of soil sulfur (S), total nitrogen (N), and organic carbon, and their interrelationships and S mineralisation were examined on a Typic Haplustert soil after a 27-year long-term cropping. The results indicated that NPK(+S) applied for 27 years at 50%, 100%, and 150% of optimum recommended rates and 100% NPK(+S) with farmyard manure (FYM) increased the organic C and total N status of soil compared with the control and the initial status of the soil. Intensive cropping with continuous use of 100% NPK without S resulted in depletion of total, organic, and inorganic S concentrations by 18.13%, 17.80%, and 21.72%, respectively, over the control, while the status of total, organic and inorganic S improved in plots that received graded rates of S with NPK and NPK plus FYM. Intensive cropping with continuous use of S-free NPK fertiliser (100% NPK-S) resulted in the widest C: N: S ratio in the soil. NaHCO 3 -extractable total, inorganic, and organic S fractions and NaOH-extractable total and inorganic S fractions were found to be better indices of soil S mineralisation than CaCl 2 -extractable inorganic S. Cumulative amounts of S mineralised during a 14-week incubation period varied between 2.3 and 21.3 mg S/kg soil and increased with an increase in the rates of S applied, along with NPK fertilisers. Incorporation of FYM with 100% NPK(+S) resulted in greater cumulative mineralised S over 100% NPK(+S) alone. The cumulative mineralised S showed a quadratic relationship with the duration of incubation in all the treatments.