Semi-arid Tropics Of India Research Articles

Nutrient availability and grain yield of winter sorghum (Sorghum bicolor (L.) Moench) as influenced by tillage practices and integrated nutrient management in Vertisols of semi-arid tropics of India

A field experiment was conducted in Vertisols at Bijapur during 1994-96 to study the effect of tillage practices and integrated nutrient management on winter sorghum yield and soil nutrient availability. The increase in winter sorghum yield with deep tillage over medium and shallow tillage was 27 and 57% in 1994-95 as compared to 18 and 34% in 1995-96. Deep tillage resulted in 22 and 45% higher yield as compared to medium and shallow tillage in the pooled data. This was mainly due to conservation and increased availability of moisture and nutrients, i.e. N, P and K. The higher availability of nutrients in the topsoil (0-0.15 m) as compared to the subsoil (0.15-0.30 m) was due to the application of nutrients in the topsoil layer and the higher rate of mineralization. Among the organic materials applied, Leucaena loppings at 2.5 t ha-1 led to a significantly (9%) higher yield (1636 kg ha-1) over vermicompost (1500 kg ha-1) and was on par with farmyard manure (1572 kg ha-1) in the pooled data and during both years of the study. The higher percentage increase in grain yield with Leucaena application was due to the better moisture conservation and availability of major nutrients, i.e. N, P and K. Winter sorghum responded significantly to N application at 25 kg ha-1 in 1994-95, whereas in 1995-96 and in the pooled data the response varied up to 50 kg N ha-1. In the pooled data, the grain yield increased by 17 and 24% with the application of 25 and 50 kg N ha-1 compared with the control. The higher yields obtained with the application of nitrogen were due to the better availability of nutrients, especially N, as these soils are low in available N.

Growth, yield, competition and economics of groundnut/cereal fodder intercropping systems in the semi-arid tropics of India

Intercropping legumes with non-legume crops during the rainy season (wet season) is a common practice in the semi-arid tropics of India. Of late, the concept of intercropping has also been utilized in irrigated (dry season) situations. In a 2-year field study during the dry season (February–May), we assessed yield, competition and economics in a groundnut/cereal fodder intercropping system compared with monocropped groundnut. Maize ( Zea mays L.), sorghum ( Sorghum bicolor (L.) Moench) and pearl millet ( Pennisetum glaucum L.) were grown for fodder. One cutting for all and two cuttings (first at 50 days after sowing and second at 95 days after sowing) for sorghum and pearl millet were made. In intercrops one row of cereal fodder was sown between every three rows of groundnut (1:3). The green fodder yields and pod yield of groundnut were lower in intercropped than in monoculture plots. The highest green fodder yield in intercrops was recorded in pearl millet with two cuts (16.5 t ha −1) followed by pearl millet with one cut (11.8 t ha −1) and sorghum with two cuts (10.7 t ha −1). In intercrops the growth and yield of groundnut were affected by cereal fodder and intensity of cutting. A significant ( ∗ P<0.05) reduction in leaf area index (LAI) and crop growth rate (CGR) was observed in the groundnut–pearl millet system over sole groundnut. Decrease in nodule mass at pod filling stages in groundnut ranged from 3.5 to 11.0% when intercropped with cereal fodders compared to sole groundnut crop. Groundnut yield was reduced more due to pearl millet and sorghum with two cuts. However, maize as the associated crop produced 9.0 t green fodder ha −1 and affected the groundnut less with respect to pod yield (5.76% reduction), yield attributes, CGR, LAI and nodule dry mass. Of the two cutting situations under intercropping, one cut gave 9.9% higher yield of groundnut as compared to two cuts. A higher land equivalent ratio (LER) and relative crowding coefficient (RCC) value leads to a crop yield advantage. Accordingly, yield advantage was greater in case of the groundnut/maize association. The competition ratio (CR) is a better indication of performance than RCC. The CRs of pearl millet and sorghum with two cuts were greater than maize but the corresponding CRs of groundnut were less. Thus, pearl millet and sorghum were more competitive, and groundnut under these two crops was affected more. The maximum monetary advantage was also recorded for the groundnut/maize intercropping system.

Breeding Prolific Garole with Malpura Sheep for Increased Reproductive Efficiency in Semi Arid Tropics of India

Garole, a prolific small sized sheep breed of West Bengal, was introduced in the Mutton project of the Institute in 1997 to explore the possibility of incorporating fecundity gene(s) into monotocus Malpura sheep of Rajasthan. Results of reproduction and production traits in respect of GarolexMalpura (GxM) half-breds have been obtained. Of 35 lambing obtained so far from the ewes of GarolexMalpura, 45.71% were twin lambing, whereas, Malpura sheep produced mostly single lamb except 2.55% twin lambing on an average. Other reproduction traits in GxM ewes such as lambing rate, litter size at birth and weaning were considerably improved over Malpura ewes. Results revealed that the fecundity genes responsible for increasing ovulation rate and litter size have been incorporated in to the GxM genotype and it might prove a valuable germ plasm towards evolving a new prolific strain of sheep. Interestingly, survivability of GxM half-breds was almost at par with the local Malpura sheep in harsh climatic conditions of semi-arid tropics. The body weights at different ages of GxM half-breds were on little lower side compared to contemporary Malpura lambs. Average kilogram of lambs weaned/ewe lambed in Malpura and GxM genetic group was 11.86 and 11.07 kg respectively. In view of minimizing the differences in body weights and kg of lambs weaned/ewe lambed between the two genetic groups, GxM ewes has to be backcrossed with Malpura rams to raise the inheritance of latter up to 75% level. However, further research is needed to reach on certain conclusions regarding net returns from such crosses.

Use of hydraulic conductivity to evaluate the suitability of Vertisols for deep‐rooted crops in semiarid parts of central India

Abstract. Detailed morphological, physical, chemical, mineralogical and micromorphological studies were carried out to identify properties that influence the yield of deep‐rooted crops in 29 Vertisols of semiarid central India, since existing land evaluation methods are not adequate to explain the yield of cotton obtained by farmers. The studies indicated that among the soil parameters, CaCO3 in the clay fraction, the exchangeable Ca/Mg ratio, exchangeable sodium percentage (ESP) and saturated hydraulic conductivity (HC) were the yield‐influencing factors. The pedogenetic relationships between the semiarid climate, formation of pedogenic calcium carbonate, exchangeable Ca/Mg, ESP and HC have been established. In view of the pedogenetic processes that ultimately impair the drainage of soils, evaluation of Vertisols for deep‐rooted crops on the basis of HC alone may help in planning and management of soils, not only in the Indian semiarid tropics, but also in similar climatic areas elsewhere.

Effect of cultural practices on soil properties, moisture conservation and grain yield of winter sorghum ( Sorghum bicolar L. Moench) in semi-arid tropics of India

A field experiment was laid out during winter seasons of 1994–1995 and 1995–1996 on deep black clayey soils (Vertisols) at Regional Research Station, Bijapur, in the northern dry zone of Karnataka State (Zone 3) of south India to evaluate the effect of cultural practices on soil moisture conservation, soil properties, root growth and yield of sorghum ( Sorghum bicolar L. Moench). Lay out of plots with in situ moisture conservation practices reduced bulk density, increased infiltration rate, porosity, improved root growth and grain yield of winter sorghum. Conservation and availability of higher amount of moisture and nutrients during various stages of crop growth with moisture conservation practices resulted in better crop growth with higher amount of dry matter production and its translocation to ear in winter sorghum. Compartmental bunding and ridges and furrows increased the grain yield by 22.8 and 25.6% (mean of 1994–1995 and 1995–1996), respectively, over flat bed with similar trend observed during 1994–1995 and 1995–1996. Among organic sources, incorporation of Leucaena loppings improved soil physico-chemical properties, conserved higher amount of moisture and increased winter sorghum yield to a greater extent than farmyard manure and vermicompost. Average grain yield (1994–1995 and 1995–1996) of winter sorghum increased by 11.7% with Leucaena application as compared to vermicompost. Grain yield increased significantly by 20% with application of 25 kg N ha −1 and further increase in nitrogen dose up to 50 kg ha −1, increased the grain yield by 30.5% in the pooled data.

Growth performance and gum production of Acacia senegal in different land forms in hot arid zone of India

Acacia senegal, is a prominent tree species of mixed xerophytic thorn forest type, which occurs in rocky hills, dry sandy tracts and sand dunes of arid and semi-arid tropics of India and Africa. The species is main source of gum arabic in many African countries, but gum production potential of this species is untapped in Indian sub-continent. In the present investigation, an attempt is made to study the growth performance and gum production of Acacia senegal under different edaphic conditions. The overall growth performance and gum production of the tree were found to be better on sandy site as compared to other edaphic sites. The study also revealed that gum production is directly co-related with diameter at breast height (dbh) of the trees. By applying simple new gum tapping technology, India could be major source of gum-arabic.

Nutrient balances—a guide to improving sorghum- and groundnut-based dryland cropping systems in semi-arid tropical India

Information on soil–plant nutrient balance in India and elsewhere is scarce and mostly generalized. A review of earlier studies on nutrient balances was done to assess their relevance for researchers, policy makers, and farmers’ understanding, to manage soil fertility for sustainable crop productivity. An on-farm nutrient balance study during 1995/1996 and 1996/1997 was designed to understand nutrient balances resulting from farmers’ practices in semi-arid tropical regions of India. This diagnostic study targeted sorghum-based cropping systems and groundnut-based cropping systems in low rainfall areas of the Indian SAT. Selection of farmers for this study was done through a systematic survey and analyses of factors effecting farmers’ decision making for nutrient inputs. Intensive plot-specific nutrient input and output measurements were carried out on 53 farmers’ fields for sorghum-based systems and 45 farmers’ fields for groundnut-based system in this study. Topsoil mineral nitrogen (N) content observed in 2 years at the beginning of the crop season in two locations of Andhra Pradesh, India, was surprisingly high and exchangeable potassium (K) contents also indicated sufficient supply in most fields. Available phosphorus (P) in the majority of fields in both locations was around threshold levels, and just sufficient for most crops. The nutrient balance in sorghum-based systems indicates a moderate to higher negative balance of potassium leading to soil mining for potassium supply in these systems. Nitrogen and P balances were generally positive. Although the groundnut-based system accumulated 53% of its N requirements through BNF, negative balances of N and K were observed mainly due to low applications of these nutrients. Application of K along with options for improving BNF of groundnut are suggested. Better nodulating groundnut cultivars and efficient rhizobium strains need to be introduced. High positive balances were observed in the systems whenever commercial crops like castor and cotton were sown in the rotation. This indicates farmers’ preferences for applying excess quantities of FYM to commercially important crops even in dryland farming systems. The replenishment costs of mined nutrients annually in different cropping systems were calculated based on current market prices of inorganic fertilizers.

Comparative effectiveness of phosphate-enriched compost and single superphosphate on yield, uptake of nutrients and soil quality under soybean–wheat rotation

Low organic matter concentration coupled with low native soil phosphorus (P) concentrations is a major constraint limiting the productivity of a soybean–wheat system on Vertisols in the Indian semi-arid tropics. In a 3-year field study (1996–99), the performance of four different composts obtained from legume straw (Glycine max Merr.L), cereal straw (Triticum aestivum), oilseed straw (Brassica juncea L.) and city rubbish were compared, and also with chemical fertilizers in terms of degree of maturity, quality of compost, improvement in soil organic matter, biological activities of soil and yields of soybean and wheat. Phospho-sulpho-nitrocomposts (phosphocomposts) were prepared containing approximately 2·5 to 4·2% P and 1·4 to 2·3% N, in an aerobic decomposition process for 4 months by adding an aqueous slurry of 1:1 (dry weight) cow dung, 2·2% P in the form of low grade Mussorie phosphate rock (7·5% P), 10% pyrite (S, 22·2%) and 0·5% urea N, and bioinoculums such as the cellulose decomposers Paecilomyces fusisporus and Aspergillus awamori, and P-solubilizing organisms i.e. Bacillus polymyxa and Pseudomonas striata. The maturity indexes were strongly associated with the source of materials, chemical composition and degree of decomposition. The matured composts had lower C/N ratios (8·2 to 21·7) and water soluble carbohydrates (0·23 to 0·43%) and larger ratios of cation exchange capacity/total organic carbon (CEC/TOC) and lignin/cellulose than the initial. The matured compost increased total P, water soluble P, citrate soluble P, total N and NO3-N and the application of phosphocompost at the rate of 10 t/ha gave plant growth dry matter accumulation, seed yield and P uptake by soybean equivalent to single superphosphate at 26·2 kg P/ha. The continuous turnover of enriched phosphocompost increased soil microbial biomass C and the activity of enzymes compared to application of chemical fertilizer.

Development of a land quality index for sorghum in Indian semi-arid tropics (SAT)

The present study demonstrates the development of crop specific land quality index (LQI) for sorghum [sorghum bicolor (L.) Moench] under semiarid tropics of India. The method developed as LQI is a function of climatic quality index (CQI) and soil quality index (SQI). The CQI defined as growth index was derived from the compound product of water satisfaction index and radiation index. The SQI was developed as multiple attributes of soil properties related to sorghum suitable soil quality such as soil depth, available water capacity (AWC), drainage and slope. The LQI was correlated with the actual sorghum yield obtained from benchmarks soils and it was found that LQI bears good agreement with the yield. From the yield correlation, the LQI class has been fixed as LQI value <1.0 rated as high, 1–1.5 as moderate and >1.5 as low corresponding to the maximum attainable yield of >50%, 40–50% and less than <40%, respectively. The study also indicated that CQI value of <0.25 and SQI value of <5 correspond to good sorghum growing area. Finally, the isoline maps of CQI and SQI maps were superimposed through TYDAC-SPAN-GIS system to arrive at LQI class map. The map indicates that out of a total area under sorghum (11.7 m ha), 43% falls under high LQI class, and 38% under moderate, and 19% under low LQI class. The moderate and low LQI areas need proper rehabilitation measures for increasing sorghum yield. The LQI developed may help in planning and management of soils not only under Indian SAT but also in areas of similar soil and climatic conditions occurring elsewhere.

Same day conversion from sigmoidoscopy to colonoscopy is a viable option for colorectal cancer screening with similar clinical and technical outcomes and greater patient satisfaction

Organic components of an Alfisol and a Vertisol in adjacent locations in Indian semi-arid tropics were characterized using chemical analysis, photometric and high resolution solid-state 13C nuclear magnetic resonance (NMR) spectroscopies, and 14C dating. The organic carbon contents of the Alfisol (0.50-0.25%) were about half the ones of the Vertisol (0.69-0.48%). Among the organic components, fulvic acids were found to be the major constituents, about 80–90% in the Alfisol and 70% in the Vertisol. These figures suggested faster organic decomposition in the Alfisol. The color intensities (K600/C) of humic acids of the Alfisol increased from the surface through deeper layers, while those of the Vertisol remained constant in all the layers. The 13C NMR measurements on the humic acids of both soils suggested the presence of polymethylene-, methyl-, N-methyl-, O-methyl-, dioxygenated-, O-alkyl-, aromatic-, phenolic or quaternary-, and carboxyl carbons. The Alfisol humic acid samples were characterized by a higher content of unsaturated (110-0 ppm) carbons and a lower content of quaternary ( 145-120 ppm) carbons than those of the Vertisol. Radiocarbon dating showed that the humic acids of the Alfisol were of modem (10 cm) through 2520 yr BP (40 cm) years old, while those of the Vertisol were in a narrower range of 4650 yr BP (10 cm) through 5440 yr BP (40 cm). Close relationships among radiocarbon dating, photometric, and NMR spectrometric characteristics of humic acids were suggested.

Yield sustainability and phosphorus utilization in soybean–wheat system on Vertisols in response to integrated use of manure and fertilizer phosphorus

Low native soil phosphorus (P) availability coupled with poor utilization efficiency of added P is a major constraint limiting the productivity of soybean–wheat system on Vertisols in Indian semi-arid tropics. The use of fertilizer P is limited by its high cost, while organic inputs generally cannot provide sufficient P for optimum crop growth due to their low P concentration. We, therefore, evaluated in a 5-year field experiment (1992–1997) the effects of integrated use of manure and fertilizer P on crop yield sustainability, P utilization and soil P fertility under soybean–wheat system on a Typic Haplustert. The treatments consisted four rates each of manure (applied only to soybean) and fertilizer P (applied to both soybean and wheat) arranged in a split-plot design with four replications. Both soybean and wheat crops responded significantly to the application of manure and fertilizer P. For the same level of P input, the yield increases were greater with manure P than with fertilizer P. Further, integrated use of fertilizer P and manure was better than their sole application in increasing and sustaining the productivity of soybean–wheat system. The P uptake by the crops increased with increasing rates of manure and fertilizer P and was relatively larger in soybean than in wheat. The per cent phosphorus recovery by the crops from fertilizer P decreased with increasing fertilizer P rate, while it was improved in the presence of manure. Though the extent of fertilizer P recovery was more or less similar in both the crops, soybean was more efficient than wheat in extracting the soil and manure P. The available P status of the soil showed a significant build-up during successive cropping seasons due to fertilizer P and the increase was strikingly greater when fertilizer P was applied in combination with manure. The integrated use of manure and fertilizer P is a promising strategy to improve soil P fertility status and to obtain higher and sustained productivity of the soybean-wheat cropping system on Vertisols of the semi-arid tropics.

Decomposition of Changes in Cereals Demand into its Components in Semi-Arid Tropical India

The purpose of this study is to decompose the observed changes in quantity demanded of cereals into its components-due to changes in income, price consumer taste and preferences and residual including other omitted variables. This will enable us to understand the relative importance of these components and evolve policies to modify the direction of changes in the demand far cereals. The main ingredients for this purpose are demand elasticities for cereals with respect to income, price and taste. These demand elasticities are estimated for each often Semi-Arid Tropical (SAT) states and all India using pooled time series of cross-sections data published by the National Sample Survey organization for the period 1972-1994. The empirical results show wide variation in demand elasticities across states, income groups and rural/urban sectors. The consumer taste and preferences captured through time trend variable is significant and negative for most of the individual states, as well as, all India. The negative effect of taste change has more than offset the positive effects of income and other variables in the model. This explains partly the decline in cereal demand over time despite rise in per capita income and fall in relative prices of cereals. The magnitudes of the effects are smaller in urban areas than rural with taste change becoming positive ill some cases. Coarse cereals exhibit negative demand responses with respect to income, own-price and taste variables, interestingly, in few cases - Andhra Pradesh. Karnataka, Madhya Pradesh and Maharashtra - consumer tastes seem to have changed in favour of -coarse cereal consumption. However the positive taste effect is nullified by negative income effect with the net result of decline in cereal demand The tests of nested hypotheses also confirm the need for inclusion of taste, income group dummies and their interaction variables in the model.

Agronomical and Chemical Studies on Tagetes minuta Grown in a Red Soil of a Semiarid Tropical Region in India

The agronomic performance and chemical composition of Tagetes minuta L. was evaluated in a new agro-climatic region of semiarid tropical India. T minuta performed well under these conditions and responded to application of 50 kg N/ha. Analysis of the leaf and flower oils by GC revealed that the leaf oil contained dihydrotagetone (6l.0%) and (Z)-tagetone (16.1%), while the flower oil was rich in (Z)-β-ocimene (47.9%) and (Z)-tagetenone (19–6%).

Determinants of farmers' indigenous soil and water conservation investments in semi-arid India

Abstract This paper investigates the determinants of farmers' indigenous soil and water conservation investments in the semi-arid tropics of India. A simple theoretical model is used to develop hypotheses about the determinants of investment under alternative factor market conditions, and these are tested using data on conservation investment from three villages. We find that conservation investment is significantly lower on leased land in two of the study villages and lower on plots that are subject to sales restrictions in one village, suggesting the potential for land market reforms to increase conservation investment. In one village, households with more adult males, more farm servants, and less land invest more in conservation, as predicted by the model of imperfect labor markets; and households with more debt and off-farm income invest more, consistent with the model of imperfect credit markets. Evidence that conservation investment is affected by factor market imperfections is weaker in the other villages, where investments are much larger, suggesting transaction costs as the source of the differences between villages. Other factors that have a significant effect on investment include the farmer's education and caste, characteristics of the plot (size, slope, irrigation status, and quality ranking) and the presence of existing land investments. The results suggest the importance of accounting for differences across communities and households in factor market and agroclimatic conditions in designing programs to promote investments in soil and water conservation.

Rainfall infiltration and runoff from an Alfisol in semi-arid tropical India. II. Tilled systems

Formation of low permeable crusts on Alfisols of semi-arid tropical India significantly affects runoff and erosion processes during rainstorms. The management options commonly used to reduce runoff are tillage and/or application of organic amendments. Daily runoff data from a field experiment conducted at International Crops Research Institute for the Semi-Arid Tropics, Hyderabad, India, were analyzed to quantify the benefits of two different types of tillages (shallow tillage to a depth of 10 cm and deep tillage to a depth of 20 cm) and application of amendments (farmyard manure at 15 Mg ha −1 yr −1 and rice straw ( Oryza sativa) at 5 Mg ha −1 yr −1) using a no-till, unamended system as a control. The no-till system is discussed in detail in Part I. Runoff from tilled plots declined sharply after tillage operation and reverted back to that from an untilled plot after a few storms totalling about 150 mm of rainfall. Consequently, the effective period of tillage varied from 5 days in 1989, when a single storm of 115 mm rain occurred 5 days after tillage, to about 60 days during 1993 and 1994. Quantitative rainfall–runoff relationships were developed by dividing 633 rainfall–runoff events over 6 years into three groups, depending on time of occurrence: fallow period, from time of tillage operation to receipt of 150 mm of rain, and the remaining events during the cropping period after 150 mm of rain to crop harvest. More than 73% of the variation in runoff from bare and farmyard manure plots could be explained by either rainfall amount or by the product of rainfall amount and 30 min intensity. In addition, soil cover was important during the fallow period. Using the 5 min rainfall intensities, we found that runoff of tilled systems may be reduced from 35% to 10% of rainfall by adding straw. The implication is that organic amendments (such as straw or farmyard manure, if available) offer a sustainable way for Alfisols to maintain a high infiltration rate and, thereby, both reduce runoff and increase the amount of water available for crop production.

Rainfall infiltration and runoff from an Alfisol in semi-arid tropical India. I. No-till systems

Alfisols, which are abundant in the semi-arid tropics, are fragile and subject to crusting, resulting in high runoff amounts and large soil losses. A field experiment was conducted at the International Crops Research Institute for the Semi-Arid Tropics, Hyderabad, India, over a 6-year period to study the runoff from Alfisols under no tillage without amendments, and with the addition of farmyard manure (15 Mg ha −1yr −1) and rice straw ( Oryza sativa) (5 Mg ha −1 yr −1). Each treatment had three replicates. A total of 211 runoff events were recorded for each plot. For runoff from no-till systems without any plant or straw cover, the infiltration rate was controlled by the surface crust. Infiltration rate through a surface crust was 9.6 mm h −1 and showed little change over time. Infiltration rates measured with a ring infiltrometer and disc permeameter were five to six times higher than that observed under natural rainfall. The data was divided into four groups with similar amounts of rain during the preceding 2 days and percent soil cover. The regression analysis found that the amount of precipitation, 30 min intensity, soil cover, and time since the beginning of the experiment were all significant factors in determining the runoff. More than 75% of the variation in runoff was explained by these variables for the zero tillage system without amendments and with farmyard manure applied. Straw amended systems were more difficult to predict. For events with less than 15 mm of rain during the previous 2 days, runoff was mainly related to the amount of rainfall when surface cover was less than 30% and to the product of rainfall amount and 30 min intensity when surface cover was greater than 30%. For events with more than 15 mm of rain during the previous 2 days, infiltration rates were generally higher than for dry soil. Runoff was related to a number of variables. Implication for management practices on Alfisols are that adding organic residue to no-till systems could significantly lower the runoff and increase the amount of water available for the crop.

Vertisol Watershed Research in the Semi-Arid Tropics: Directions for Impact Assessment

The application of watershed management research in semi-arid tropics of India has been well researched at International Crop Research Institute for Semi-Arid Tropics (lCRISAT). The present paper is a review of watershed development technology and its benefits accrued to the farmers in the semiarid tropics as reflected in the research work of ICRISAT. The paper focuses on the technology, as well as, the benefits flowing from the watershed technology as visualised in various ICRISAT studies. Apartfrom the analysis the paper draws a few lessons from the experiences gathered from the studies conducted by ICRISAT.

MEASUREMENT OF NITRATE LEACHING POTENTIAL OF A VERTISOL USING BROMIDE AS A TRACER UNDER RAINFED CONDITIONS OF THE INDIAN SEMI-ARID TROPICS

High temperatures and evaporation in summer (April-June) and erratic rainfall in the wet season (July-September) are common features of the harsh environment of Indian semiarid tropics (SAT). The rainfall of this region often occurs in large storms punctuated by discrete dry spells. During excessive rainy periods there is a strong possibility that a large part of the resident soil-N, especially NO − [over] 3, NO − [over] 2 etc., may move beyond the root zone with the excess water percolating down the soil profile. To understand the N losses through leaching in a deep Vertisol (depth > 150 cm) of the Indian SAT, a field experiment was conducted during the "wet" season (June-September) of 1992 under rainfed conditions, using bromide (Br−) as a tracer for NO − [over] 3. Bromide (as NaBr) at 200 kg ha−1 was applied onto the surface of a bare fallow soil, in microplots (200 × 200 cm2), on June 15, and its vertical movement to 100 cm was monitored weekly. Results showed that Br− distribution was influenced strongly by rainfall. After 1 week (June 15-22), with a rainfall of 64 mm, Br− was found to a depth of 60 cm, and whereas most (40%) was in the top layer (0-10 cm), a total of 90% of applied Br− was recovered to a depth of 60 cm. With large storms occurring in early July (e.g., 68 mm on July 2), Br− was moved further down the profile and accumulated largely in the 30 to 40-cm layer. In early August, because of continuous heavy rainfall, almost all Br− had migrated beyond 50 cm depth. Approximately 40% was not found within the profile (0-100 cm) on September 11. In dry spells during late August and early September, upward movement of 10 to 20% of Br− was also noticed at 60 to 100 cm depth. Thus, the results demonstrate that early August may be a critical period for maximum NO − [over] 3 leaching in this soil and emphasize the need of advance strategies to reduce these effects in view of increasing need for N use efficiency and reduction of ground water contamination.

Nitrogen and/or phosphorus fertilization effects on organic carbon and mineral contents in the rhizosphere of field grown sorghum1

The effects of nitrogen (N) and/or phosphorus (P) fertilizers on the nutritional status in the rhizosphere were studied by monitoring throughout the growth period the concentrations of organic carbon (C), inorganic N, NaHCO3 extractable P, exchangeable K, Ca, and Mg in sorghum (Sorghum bicolor L. Moench) down in an Alfisol field, and of all these elements except for extractable P, and exchangeable Ca in a Vertisol field in semi-arid tropical India. These concentrations were compared between the rhizosphere soil and bulk soil of sorghum grown in both fields. Organic C content of the rhizosphere soil increased with plant age and was significantly higher than that in the bulk soil throughout the growth of sorghum, but it was not affected by the rates of N or P fertilizer. Inorganic N concentration in the rhizosphere soil was significantly higher than that in the bulk soil until maturity in sorghum. The content of available P in the rhizosphere soil was significantly higher than in the bulk soil after the middle of the growth stage. Its average concentration in the rhizosphere soil across growth stages was significantly higher than in the bulk soil, which contradicts the observation in many reports that there is a depletion of P in the rhizosphere soil. The concentration of three exchangeable cations, K, Ca, and Mg, showed different patterns in the rhizosphere and the bulk soils. The concentration of K was almost constantly higher in the rhizosphere soil than in the bulk soil, Ca concentration was not different between the two soils, and Mg concentration was significantly higher in the bulk soil than in the rhizosphere soil. The reasons for these discrepancies cannot be explained at present. The concentrations of these cations were not affected by the rate of N or P fertilizer except for Mg at a later growth stage. The differences between rhizosphere and bulk soils in Alfisol were similar to those in Yertisol with respect to the concentration of organic C, inorganic N, and exchangeable K and Mg.

Effect of Irrigation and Levels of Nitrogen on Herb and Oil Yield of Geranium (Pelargoniumsp.) under Semiarid Tropical India

ABSTRACT The effect of irrigation given at various cumulative pan-evaporation levels (CPE) (50, 75 and 100 mm) and three depths of irrigation water (IW) (20, 30 and 40 mm per irrigation) in Bangalore was studied. The irrigation at four IW/CPE ratios (1.0, 0.50, 0.30 and 0.25 mm, with 30 mm depth of irrigation water) and three nitrogen levels (0, 100 and 200 kg N/ha/year) was also studied. Results revealed that irrigation at 50 mm CPE with 30 mm depth of irrigation gave the optimum herb and oil yield and the other experiment showed that geranium has to be irrigated at 0.50 IW/CPE ratio and supplied with 100 kg N/ha/year for achieving high yields. Content and quality of oil were not affected by irrigation and levels of nitrogen.