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The effect of varying the sulfur (S) and nitrogen (N) supply on theyield and composition of brown rice (Oryza sativa L.)grainwas studied to determine whether grain analysis could be used for the diagnosisof S deficiency in this crop. Plants were grown to maturity in an S deficientyellow podzolic soil, under flooded and upland conditions in a glasshouse. Inthe first experiment there were six application rates of S combined with threeapplication rates of N. The amount of grain per plant varied from 0.69 to 7.62g, depending on the level of S and N supplied. Rice grown underflooded conditions produced approximately twice the grain yield of upland ricegrown at field capacity. Grain from the flooded series generally had a lower Sconcentration, and apart from the grain from the low N treatment, had lower Nconcentrations than the grain from the upland series. The grain S concentrationvaried from 0.069% to 0.154% and the N concentration ranged from 1.06% to 2.14%with changing S and N supply. Strong positive relationships were obtainedbetween grain yield and grain S concentration, and negative relationshipsbetween grain yield and the N:S ratios in the grain. The critical Sconcentration determined for 90% maximum yield in plants well supplied with Nwas not sufficient to distinguish between S responsive and unresponsive plantswhen N was limiting; both grain S concentration and N:S ratio are necessary todetermine the S status of the rice crop. Deficiency was indicated when the Scontent of the grain was less than 0.1% and the N:S ratio was wider than 14:1,and the same criteria applied to rice grain from flooded and upland treatments.Note that these values were derived in a glasshouse experiment using one ricecultivar on one soil and are therefore preliminary and require confirmationbefore practical application in the field. The second experiment examined theeffect of supplemental S applied after anthesis on grain composition. Latesupplemental S had no effect on grain yield, or on the composition of grainfromplants adequately supplied with S. In marked contrast, S concentration in grainof previously S deficient plants increased from 0.08% to 0.2%, well above thehighest level achieved by applying S at sowing. It is concluded that grainanalysis can be used to diagnose retrospectively S status for yield, provided Ssupply does not increase between the stage when grain yields are beingdetermined and the subsequent grain filling stage. An increase in S supplybetween these two stages will change the relationship between grain Scomposition and yield and complicate interpretation of grain analysis fordiagnosis. The advantages of using grain analysis for retrospective diagnosisofS deficiency are discussed, and the preliminary results suggest that theconcepts warrant further testing in the field.

Surface soil samples (0–15 cm) from six differentially fertilized plots (N0P0K0, N120P0K0, N120P17.5K0, N120P35K0, N120P17.5K33.2 and N120P35K33.2) of a long-term experiment on maize-wheat annual sequence at Ludhiana (India) were collected after 11 years of continuous cropping and fertilization, to study soil phosphorus (P) adsorption-desorption. These soils differed widely with respect to their P adsorption and desorption properties. Phosphate adsorption increased with increasing levels of added P in all soils. The extent of P adsorption was comparatively lower in the plots receiving P. Phosphorus adsorption data was found to fit best both to Langmuir and Freundlich isotherms for each of the six soil samples. Soil P adsorption maxima obtained from Langmuir isotherm varied from 123 to 498µg g−1 soil in the six differentially fertilized plots. The bonding energy values obtained from Langmuir isotherm plot were the lowest in control and N120P0K0 treatments whereas these values tended to increase with P addition. Freundlich constants ‘a’ and ‘n’ (extent and rate of adsorption) calculated from the regression lines also showed similar trend for the six soil samples. The plot of desorbed P versus desorbed P/adsorbed P was linearly correlated for each of the six soil samples. Computation of desorable P capacity (or desorption maxima, Dm) and desorption rate constant (Kd) from this relationship indicated higher Dm values in soil samples collected from check (N0P0K0) and N fertilized (N120P0K0) plots. This value tended to decrease in plots which received P during cropping. The Kd values were more in soil samples which were fertilized with P during croping and lower in check and N120P0K0 treated plots.

Data from 194 published pot and field experiments were used to calculate the fertilizer effectiveness of two commercially available calcined iron-aluminium rock phosphate fertilizers— Calciphos and Phospal. A very wide range of effectiveness values (RE) relative to superphosphate have been reported for freshly applied fertilizers ( < 0.1 to 3.0). These differences are primarily not due to differences in citrate soluble P, soil pH, plant species and mean annual rainfall. For both fertilizers most of the variation in published values is due to the use of poorly responsive soils and to incorrect methods of fertilizer assessment. Lower RE values (< 0.1 to 0.5) were derived for experiments on highly P responsive soils and when several levels of P were applied to provide complete response curves. For these experiments high RE values (about 1.0) for Calciphos only occurred for sandy soils in which water-soluble P was rapidly leached. The residual value of Calciphos and Phospal remained low relative to freshly applied superphosphate.

Studies have been undertaken in a 1000 ha area of irrigated rice (Oryzica sativa) at Caroni (1975) Limited to determine the effect of the fertilizer programme on the incidence of important diseases. Over a period of three years higher levels of brown leaf spot (Cochliobolus miyabeanus) on rice varieties Oryzica 1 and Oryzica 5 on three different soil types were associated with increasing levels of leaf P, from a low of 0.149% of dry matter (DM) to a high of 0.396% DM. On the Washington silty clay loam series (Inceptisol) brown leaf spot incidence was lowest when leaf P was between 0.135% and 0.149% of DM. However, disease incidence was higher when leaf P levels fell to 0.133% of DM or rose above 0.149%, under conditions where N was more than adequate. The moderate levels of the disease experienced over the period had no effect on yield, as grain infection was minimal. The results support the conclusion that the incidence of brown leaf spot on irrigated rice at Caroni is influenced by sub-optimal levels paticularly of P. Careful monitoring and managememt of P nutrition is seen as an important part in the overall strategy for controlling the disease.

Organic carbon is known to alter crop response to applied phosphorus (P) but that fact has not been incorporated in soil test interpretations. To achieve this objective, field experiments with wheat were conducted for four years on alkaline soils of Punjab, India. The experimental soils ranged from loamy sand to loam in texture, 7.4 to 9.6 in pH, 0.16 to 0.75% in organic carbon (OC) and 2 to 40 mg Olsen extractable P kg−1 soil. Response of wheat to fertilizer phosphorus application was related to the combined effect of Olsen P and soil OC content. At a given Olsen P level, wheat yield was a function of soil OC content. Multiple regression analysis of the data showed that OC content <0.2% did not affect yield significantly. At values >0.6%, OC along with Olsen P accounted for 97% of the variation in yield and there was no response to applied fertilizer P. Yield isoquants for 4 and 5 tons grains ha−1 showed that for a given Olsen P level, as OC content increased the amount of fertilizer P required to achieve a yield target decreased. It was shown that OC may be used to approximate the contribution of organic P mineralization to plant available soil P during a growing season. The reliability of fertilizer recommendations based on Olsen P may be improved on some alkaline soils by consideration of soil OC content.

Field and pot culture experiments were conducted in terai acid soil (Haplaquoll) to evaluate the fertilizer value of one basic slag and two rock phosphates, such as Purulia rock phosphate (Igneous) and Mussoorie rock phosphate (sedimentary). In the field experiments two crop sequences were followed: (i) Rice — wheat — greengram (ii) Greengram — rice — wheat. In terms of crop yield and P uptake Purulia rock phosphate did not show any significant effect, except in case of greengram grown as the third crop after its application. Mussoorie rock phosphate increased the yield and P uptake through its direct and residual effect in all the crops, except in rice. Irrespective of crop species and crop sequences basic slag showed considerable direct and residual effect in increasing the crop yield and P uptake. Its effect was at par with that of superphosphate. By total yield increase of three consecutive crops due to added P the efficiencies of the fertilizers were graded as basic slag > superphosphate = Mussoorie rock phosphate > Purulia rock phosphate for rice — wheat — greengram rotation and superphosphate > basic slag > Mussoorie rock phosphate > Purulia rock phosphate for greengram — rice —wheat rotation. Composting improved the efficiency of all the insoluble phosphatic fertilizers.

Organic matter is important to sustain and improve soil quality and productivity. A field experiment determined the effects of 27 annual spring surface-broadcast applications of ammonium nitrate at 0, 112 and 224 kg N ha−1 year−1 to bromegrass (Bromus inermis Leyss) on light fraction organic matter (LFOM), total amino acids, amino acid C (AAC) and N (AAN), ammonium–N (NH4–N) and, total organic matter (TOM) in a thin Black Chernozemic loam soil at Crossfield, Alberta, Canada. The concentration and mass of LFOM, AAC and AAN in the 0–5, 5–10 and 10–15 cm soil layers increased with N rate, with greatest increase in the 0–5 cm layer. The response to N application was much greater for LFOM than for TOM. The changes in soil LFOM, AAC, AAN, NH4–N and TOM suggest that N application increases the quantity of light fractions and improves the quality of total organic matter in the soil.

The global warming potential of nitrous oxide (N2O) and its long atmospheric lifetime mean its presence in the atmosphere is of major concern, and that methods are required to measure and reduce emissions. Large spatial and temporal variations means, however, that simple extrapolation of measured data is inappropriate, and that other methods of quantification are required. Although process-based models have been developed to simulate these emissions, they often require a large amount of input data that is not available at a regional scale, making regional and global emission estimates difficult to achieve. The spatial extent of organic soils means that quantification of emissions from these soil types is also required, but will not be achievable using a process-based model that has not been developed to simulate soil water contents above field capacity or organic soils. The ECOSSE model was developed to overcome these limitations, and with a requirement for only input data that is readily available at a regional scale, it can be used to quantify regional emissions and directly inform land-use change decisions. ECOSSE includes the major processes of nitrogen (N) turnover, with material being exchanged between pools of SOM at rates modified by temperature, soil moisture, soil pH and crop cover. Evaluation of its performance at site-scale is presented to demonstrate its ability to adequately simulate soil N contents and N2O emissions from cropland soils in Europe. Mitigation scenarios and sensitivity analyses are also presented to demonstrate how ECOSSE can be used to estimate the impact of future climate and land-use change on N2O emissions.

The pH of manure pellet fertilizer can affect the nitrous oxide (N2O) emission from soil, although its effectiveness and the relative mechanisms are not well understood. This study aims to quantify the effect of cattle-manure-based pellet pH on N2O emissions from an Andosol field. The field experiment consisted of four treatments: chemical (mineral) fertilizer (CF), cattle-manure-based pellet fertilizer of pH 5.6 (OP), cattle-manure-based pellet fertilizer of pH 7.1 (NP), and cattle-manure-based pellet fertilizer of pH 10.1 (AP). Cumulative N2O emission over the 365 days in the OP and NP treatments was 59.4% and 49.3% lower than that in the AP treatment, respectively, but the cumulative N2O emissions were statistically significant only between the OP and AP treatments. Moreover, cumulative N2O emission in the pellet fertilizer treatments during the peak period after fertilization in the autumn and spring cropping seasons (total 70 days) increased with increasing pellet pH. In the pellet fertilizer treatments, soil nitrification potential, soil N2O production rate, and total denitrification rate of soil also clearly increased with the increase of pellet pH. Therefore, slightly acidic pellet pH (OP treatment) may have inhibited the microbial N2O production processes in comparison to the neutral pellet pH (NP treatment), but alkaline pellet pH (AP treatment) could have stimulated the microbial N2O production processes than the neutral pellet pH. These results suggested that increased N2O emission with an increase in pellet pH may be attributed to a change in the N2O production rate via nitrification and denitrification.

Fall application of N fertilizers is often inferior to spring application for increasing yields of spring-sown cereal grains. The objective of this study was to determine the influence of date of application on efficiency of fall-applied N. Fall application dates were related to recovery of fall-applied N as mineral N in soil in spring, and related to yield and N uptake for spring-sown barley. Urea at a rate of 50 or 56 kg N ha−1 was incorporated into the soil to a depth of 10 cm. There were 2 or 3 application dates in the fall and one in the spring at sowing. Linear regression indicated recovery of fall-applied N as soil mineral N in spring increased from 30% with urea added on 19 September to 79% with addition on 6 November, but the predictability was low (r = 0.54**). Increase in grain yield, expressed as relative efficiency of fall- versus spring-applied N, was only 23% on 19 September but rose to 76% by 6 November (r = 0.68**). Results were similar for N uptake in grain. Other approaches to predicting the relative efficiency of fall- versus spring-applied N for yield increase were based on fall soil temperature at 5 cm depth, instead of fall calendar date. Soil temperature on the day of N application gave inferior correlation (r = −0.55**), but the use of number of days from application to first day of 0°C soil temperature gave a fairly close correlation (r = −0.77**). Soil degree-days accumulated from application to first day of 0°C soil temperature gave a similarly close correlation (r = −0.78**). In all, the efficiency of fall-applied urea was markedly increased by delaying the application into the late fall; and calendar date, number of days or soil degree-days from application to soil freezing all predicted the efficiency fairly well.