P. N. Takkar

Effects of repeated manure and fertilizer phosphorus additions on soil phosphorus dynamics under a soybean-wheat rotation

Abstract Soil P availability and efficiency of applied P may be improved through an understanding of soil P dynamics in relation to management practices in a cropping system. Our objectives in this study were to evaluate changes in plant-available (Olsen) P and in different inorganic P (Pi) and organic P (P0) fractions in soil as related to repeated additions of manure and fertilizer P under a soybean-wheat rotation. A field experiment on a Typic Haplustert was conducted from 1992 to 1995 wherein the annual treatments included four rates of fertilizer P (0, 11, 22 and 44 kg ha–1 applied to both soybean and wheat) in the absence and presence of 16 t ha–1 of manure (applied to soybean only). With regular application of fertilizer P to each crop the level of Olsen P increased significantly and linearly through the years in both manured and unmanured plots. The mean P balance required to raise Olsen P by 1 mg kg–1 was 17.9 kg ha–1 of fertilizer P in unmanured plots and 5.6 kg ha–1 of manure plus fertilizer P in manured plots. The relative sizes of labile [NaHCO3-extractable Pi (NaHCO3-Pi) and NaHCO3-extractable P0 (NaHCO3-P0)], moderately labile [NaOH-extractable Pi (NaOH-Pi) and NaOH-extractable P0 (NaOH-P0)] and stable [HCl-extractable P (HCl-P) and H2SO4/H2O2-extractable P (resisual-P)] P pools were in a 1 : 2.9 : 7.6 ratio. Application of fertilizer P and manure significantly increased NaHCO3-Pi and -P0 and NaOH-Pi, and -P0 fractions and also total P. However, HCl-P and residual-P were not affected. The changes in NaHCO3-Pi, NaOH-Pi and NaOH-P0 fractions were significantly correlated with the apparent P balance and were thought to represent biologically dynamic soil P and act as major sources and sinks of plant-available P.

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

Abstract 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.

Growth and reproduction of the vermicomposting earthworm Perionyx excavatus as influenced by food materials

An outdoor study was undertaken using polyethylene containers to assess the suitability of different organic residues, soybean straw (Glycine max L. Merril.), wheat straw (Triticum aestivum L.), maize stover (Zea mays L.), chickpea straw (citer arietinum L.) and city garbage, as food for the tropical epigeic earthwormPerionyx excavatus, and to assess the influence of this earthworm on the decomposition of these materials. Maize stover was found to be the most suitable of the food materials used. Population growth ofP. excavatus was enhanced by addition of these organic materials in the temperature range 24°-30°C, while the population was adversely affected above 30°C in a vermiculture system. Addition of earthworms accelerated the breakdown of residues, which ultimately resulted in a lowering of the C:N ratio, water-soluble carbon and carbohydrates, and increased ash percentage and cation exchange capacity compared with their respective controls.

Malachite green method compared to ascorbic acid for estimating small amounts of phosphorus in water, 0.01M calcium chloride, and Olsen soil extracts

Abstract Malachite green method has been evaluated for estimating minute quantities of phosphorus (P) in water, 0.01M calcium chloride (CaCl2), and Olsen [sodium bicarbonate (NaHCO3)] extracts often soils of varying properties. The precision and accuracy of the malachite green method was better than that of the ascorbic acid method to estimate P in these three extracts. The recovery of added P ranged from 95.3–99.3% in water, 96–100% in 0.01M CaCl2, and 96.7–100% in Olsen extracts. The ascorbic acid method underestimated the amounts of 0.01M CaCl2‐P and its precision was also lower than the malachite green method. It is possible to predict the P concentration in the three extracts equal to malachite green method from the ascorbic acid P values by using regression equations.

Transformation of fertilizer P in a Vertisol amended with farmyard manure

Availability, fixation, and transformation of added P were studied in a 16-week incubation experiment with a Vertisol amended with farmyard manure in pots with 500 g soil each. P availability, as measured by Olsen P, decreased for up to 8 weeks with various rates of added P, when no manure was applied. In the presence of farmyard manure, P availability decreased during the first 6 weeks and then showed a considerable increase from the 8th week onwards. P fixation increased for up to 8 weeks with the rates of P in the absence of manure. With manure application, P fixation increased only during the first 6 weeks and thereafter decreased continuously. Thus the presence of farmyard manure shortened the period of P fixation and promoted its availability. After 16 weeks of incubation, when manure and fertilizer P were applied together, P was transformed into labile organic (NaHCO3−P), moderately labile organic P (NaOH-P), and calcium-bound inorganic P (HCl-P). When manure was not applied. P accumulated predominantly as labile inorganic (NaHCO3−P), moderately labile inorganic (NaOH-P), and inorganic HCl-P. The application of farmyard manure enriched long-term P fertility through NaHCO3−P and NaOH−P and a shortterm P supply as HCl-P. All fractions except inorganic NaOH-P showed good relationships with Olsen P.

Evaluation of several methods for determining the potassium content in diverse plant materials

Abstract Different plant analysis methods including varied incubation times with 0.5N and IN hydrochloric acid (HCl), diacid [nitric (HNO3) and perchloric (HClO4) acids], triacid [HNO3, sulfuric acid (H2SO4) and HClO4], H2SO4+hydrogen peroxide (H2O2) (Wolf method), and 0.5N and lN ammonium acetate (NH4OAc) were evaluated for measuring the potassium (K) concentration in straw and grain samples of cereal, legumes, oilseed crops, and fruit‐tree leaves. The average K concentration in nine plant materials indicated that K extracted by 0.5N and lN HCl for 5 minutes, 1 hour, and 17 hours contact periods did not differ significantly. But the amount of K extracted by these acidic solutions gradually decreased during incubation, possibly due to reabsorption of released K by the plant material. The amount of K released in to the 0.5N HCl and IN HCl extractants was in close agreement with that obtained with the standard triacid method. The IN NH4OAc extraction method slightly overestimated the K concentration in the ...

Residual effects of phosphorus applied to soyabean or wheat in a soyabean–wheat cropping system on a typic haplustert

During a 3-year experimental period (between 1992 and 1995), residual effects on yields of subsequent crops of phosphorus applied either to soyabean or wheat, and on recoveries of the added P and changes in the available P, were studied in a soyabean-wheat cropping system on a typic haplustert very low in available P at Bhopal, India. Phosphorus was applied at rates of 0-52 kg P ha -1 (five treatments) to soyabean and 0-39 kg P ha -1 (three treatments) to wheat during the first year, and in the subsequent years the residual effects were studied in relation to fresh applications of 39 kg P ha -1 to each crop. The yields of soyabean and wheat were increased significantly by the application of P to each crop. Phosphorus applied to soyabean showed residual effects in two succeeding crops, whereas P applied to wheat showed a residual effect in only one succeeding crop. Phosphorus applied to soyabean was more efficiently utilized by the succeeding crops compared to that applied to wheat in the rotation. The recoveries of added P were greater with smaller rates of added P and greater in the first two residual crops. Olsen P in soil was adequate only in the first year and it fell below the critical limit in the subsequent two cycles of cropping. Cumulative P uptake by crops determined the levels of available P in the soil and soil test values declined with increase in cumulative P uptake over time.

Organic Manure Based Phosphorus Supply Strategies: Effects on Crop Yield and Soil Test Maintenance P Requirement under Soyabean-Wheat System

ABSTRACT Assessing soil test maintenance P requirement of a given production system in relation to P supply strategies is of critical importance for judicious and efficient use of inorganic and organic p inputs. Field experiments with soyabean-wheat annual rotation on a Vertisol were conducted for three years to (i) assess the effects of p supplied through different strategies involving fertilizer and cattle manure on crop yield, P uptake and soil test p status, and (ii) determine soil test maintenance P requirement and its relation to P removal by crops. The treatments for the field experiment consisted of a control (no P check) and nine combinations of three annual P rates (P1= 26, P2 = 39 and P3 = 52 kg P ha−1, with the amount of P applied to soyabean and wheat being in the ratio of 1.6:1.0) and three P supply strategies (PSS-I = fertilizer-P for both soyabean and wheat, PSS-II = cattle manure-P for soyabean and fertilizer-P for wheat, and PSS-III = cattle manure-P + fertilizer-P on 1:1 P basis for soyabean and fertilizer-P for wheat). The soyabean and wheat crops responded significantly to P application under all the P supply strategies. The crop yield increases due to P input were, however, strikingly larger under PSS-II and PSS-III than under PSS-I. Agronomic efficiency of P (yield increment per unit of P applied) also indicated the superiority of the PSS-III and PSS-II over the PSS-I. The P uptake by crops in soyabean-wheat rotation increased significantly and linearly with increasing P rate under all the P supply strategies. During three cycles of annual soyabean-wheat rotation, the soil test P in the plot receiving no P (P0 control) declined from the initial 5.84 to 2.40 mg kg−1, while it showed a marked build-up with P application particularly at higher rates. The annual soil test maintenance P requirement (STMPR) was lower by 27–33% under PSS-II (26.3 kg P ha−1) and PSS-III (24.1 kg P ha−1) than under PSS-I (36.1 kg P ha−1). Despite these differences in STMPR, the crop yields achievable at STMPR were interestingly more or less similar across all the P supply strategies. In terms of P removal by crops, the STMPR equalled or slightly exceeded the P removal by crops under the PSS-III and PSS-II, while it was 1.4 times the removal under PSS-I. Therefore, the use of manure-P as a component of P supply strategies can help reduce the amount of P required to maintain soil P fertility and hence increase P utilization efficiency.