Agronomic Effectiveness Research Articles

Enhancing the agronomic effectiveness of natural phosphate rock with poultry manure: a way forward to sustainable crop production

Phosphorus inputs are required in highly weathered tropical soils for sustainable crop production. However, high cost and limited access to mineral P fertilizers limit their use by resource-poor farmers in West Africa. Direct application of finely ground phosphate rock (PR) is a promising alternative but low solubility of PR hampers its use. Co-application of PR with manure could be a low cost means of improving the solubility of natural PR and improve their agronomic effectiveness. Our objective was to quantitatively estimate the enhancement effect of poultry manure on P availability from low reactive PR (Togo phosphate rock) applied to highly weathered soils. We utilized two highly weathered soils from Ghana and Brazil for this greenhouse study. Using 32P isotopic tracers, the agronomic effectiveness of poultry-manure-amended Togo rock phosphate (TPR) was compared with partially acidulated Togo rock phosphate (PAPR) and triple superphosphate (TSP). Four rates of poultry manure: 0, low (30 mg P kg−1 soil), high (60 mg P kg−1 soil) and very high (120 mg P kg−1 soil) were, respectively, added to a constant amendment (60 mg P kg−1 soil) of the P sources and applied to each pot of 4 kg soil. A Randomized Complete Block Design was used for the greenhouse experiment and Maize (Zea mays L.) was used as a test crop. The plants were grown for 42 days after which the above ground biomass was harvested for analysis. Without poultry manure addition, the agronomic effectiveness, represented by the relative agronomic effectiveness (RAE) and proportion of P derived from fertilizer (% Pdff) was in the order TSP > PAPR > TPR = control (P0). In the presence of low rate poultry manure addition, the agronomic effectiveness followed the order TSP > PAPR = PR > P0. However, at the high and very high rates of poultry manure addition, no significant differences in agronomic effectiveness were observed among the P sources, suggesting that at this rate of poultry manure addition, PR was equally as effective as TSP. The study showed that direct application of PR co-applied with poultry manure at a 1:1 P ratio will be a viable option for P replenishment. Thus a combination of PR and poultry manure could be a cost-effective means of ensuring sustainable agricultural production in P-deficient, highly weathered tropical soils.

Crop (Maize) Response to Direct Application of Local Phosphate Rock on Selected Acid Soils of Tanzania

To alleviate P deficiency in Tanzania and elsewhere, direct application of local phosphate rock (PR) can be an attractive alternative to imported fertilizers, for example, triple superphosphate (TSP), provided crop responses to PR and TSP are comparable. The deposit at Minjingu (MPR) in Tanzania consists of hard MPR and soft MPR. These PRs were compared with each other and with TSP on four acidic soils low in plant‐available Ca and P in a greenhouse experiment by determining relative maize yield, P uptake, and relative agronomic effectiveness (RAE). TSP produced significantly stronger responses than MPRs but only with the first crop (RAE=40–70%), whereas MPRs were more effective with a second crop (RAE=106–150%). Similar responses to hard and soft MPR (and TSP with a second crop) indicate that the currently unutilized hard MPR, which constitutes 60% (4.8×106 Mg with 10.6% P) of the Minjingu phosphate deposit, can be utilized.

Analysis of Phosphate Rock Dissolution Determining Factors Using Principal Component Analysis in Some Acid Indonesian Soils

Dissolution of phosphate rock (PR) materials and its subsequent phosphorus (P) availability to plants depend upon soil characteristics, PR characteristics, type of crops, and environmental conditions. Agronomic effectiveness of the PR sources has frequently been investigated in the field or in the greenhouse. This is time consuming and not cost‐effective. Therefore, identification of the soil characteristics influencing the dissolution of PR is very important for direct application of P sources. The principal component analysis was used to summarize the characteristics of acid soils in an incubation system into a number of factors that may affect PR dissolution. Three major factors were selected in this study: 1) soil texture, 2) soil acidity, and 3) fertilization. Using the scores of the individual factors as independent variables, a stepwise regression analysis was performed to derive a PR dissolution function. The coefficient of determination (R2) reached 0.91**, and the magnitude of the different factors affect PR dissolution following the order of soil texture (54%)>soil acidity (43%)>fertilizer (3%). Fertilizer was not significant as a PR dissolution factor.

A laboratory and glasshouse evaluation of chicken litter ash, wood ash, and iron smelting slag as liming agents and P fertilisers

Standard AOAC methods of chemical analysis have been used to characterise the industrial byproducts partly burnt chicken litter ash (CLA), totally burnt chicken litter ash (CLAT), wood ash (WA), and iron smelting slag, for use as a combined liming agent and phosphate (P) fertiliser. These materials are effective liming agents with calcium carbonate equivalence of 93–99%. Total P concentrations of CLA (3.6% P), CLAT (4.75% P), slag (0.26% P), and WA (0.44% P) indicate that they would function as P fertilisers when applied at the high rates required for liming soils. The form of P in slag is unknown; CLA and CLAT consist mostly of mixtures of the phosphate mineral apatite with calcite and quartz. WA consists mostly of calcite, quartz, and various salts. For long extraction times, total P dissolved increased in the sequence CA (citric acid) > NAC (neutral ammonium citrate) > AAC (alkaline ammonium citrate). Little apatite persisted in residues of CLA and CLAT after 120 h of CA extraction but considerable amounts of apatite remained in NAC and AAC residues. A glasshouse P-response experiment was carried out with ryegrass on an acid lateritic soil with the application of various levels of phosphate as chicken litter ash, iron smelting slag, and wood ash. Monocalcium phosphate (MCP), dicalcium phosphate (DCP), and rock phosphate (RP) were included for comparison purposes. Based on plant yield data, the relative agronomic effectiveness (RE) of DCP compared to MCP was 57%, 72%, 73%, and 94%, respectively, for 4 successive harvests, for RP was 24%, 34%, 70%, and 56%, for chicken litter ash was 13%, 16%, 33%, and 39%, for slag was 8%, 9%, 16%, and 10%, for WA was 6%, 9%, and was effectively zero for the final 2 harvests. For no extraction time was the P soluble in the 3 citrate extractants a reliable predictor of the agronomic effectiveness of these materials as P fertilisers established by plant growth measurements.

Improving rock phosphate availability through feeding, mixing and processing with composting manure

The objective of this study was to improve the availability of phosphorus (P) from rock phosphate (RP) through feeding, mixing and composting manure. The experiment was conducted as a 3 × 2 split-plot design. Manure was collected from 12 Boran steers (200 ± 4.5 kg live weight) fed a basal diet of Napier grass ( Pennisetum purpureum) at 2.5% body weight on a dry matter (DM) basis. The main plot treatments were (i) manure from steers supplemented with 113 g Busumbu rock phosphate (BRP) per day (FBRP), (ii) manure from steers not supplemented with BRP, feces mixed with 113 g BRP per day (MBRP) and (iii) manure from steers not supplemented with BRP and feces not mixed with BRP (CONT). The sub-plots comprised composting the manure either (i) mixed with 440 g of wheat ( Triticum aestivum L.) straw per kg fresh feces (WS) or (ii) without straw (WOS). The manure was composted in 200 L plastic bins for 90 days. After 90 days, P availability was evaluated (i) by aerobic laboratory incubation at 25 °C for 1, 2, 4, 8, 12, and 16 weeks and (ii) by greenhouse agronomic evaluation study using maize ( Zea Mays L.) as the test crop in either a humic Nitosol or an Andosol. In the laboratory incubation study, resin P was higher ( p < 0.05) for the WS compost than for the WOS compost; values were higher ( p < 0.05) for the Andosol than for Nitosol and followed the order of FBRP–WS, Andosol > FBRP–WS, Nitosol > MBRP–WS, Andosol > MBRP–WS, Nitosol > FBRP–WOS, Andosol > FBRP–WOS, Nitosol. In the greenhouse evaluation, maize crops in the WS compost had higher ( p < 0.05) biomass yield than the reference fertilizer, triple super phosphate, (173% versus 196%; Andosol and Nitosol, respectively). The biomass yield and P uptake relative agronomic effectiveness (RAE) for WS compost was also higher ( p < 0.05) than that of WOS compost (184 versus 3 ± 0.8 and 242 versus 162 ± 0.2, WS and WOS, biomass yield and P uptake, respectively). Nitosol biomass yield and P uptake RAE were also higher ( p < 0.05) than for the Andosol (99 versus 88 ± 0.8 and 332 versus 72 ± 0.2, Nitosol and Andosol, biomass yield and P uptake, respectively). The results show that P-enriched composting in the presence of wheat straw significantly increased P availability and increased plant growth. However, in terms of plant growth, there was no additional benefit of first feeding the RP to steers before composting the manure because most of the RP fed seem to have been utilized by the animal.

Plant- and microbial-based mechanisms to improve the agronomic effectiveness of phosphate rock: a review

Deficiency in plant-available phosphorus is considered to be a major limiting factor to food production in many agricultural soils. Mineral resources are necessary to restore soil phosphorus content. In regions where conventional fertilizers are not used due to cost limitations or to mitigate adverse environmental effects, local sources of phosphate rock are being increasingly recognized for potential use as alternative phosphorus fertilizers. The main obstacle associated with using directly applied ground phosphate rock is that the phosphate released is often unable to supply sufficient plant-available phosphorus for crop uptake. Plantand microbial-based mechanisms are low-cost, appropriate technologies to enhance the solubilization and increase the agronomic effectiveness of phosphate rock. Common mechanisms of phosphate rock dissolution including proton and organic acid production will be reviewed for both plants and microorganisms. This review will also address possibilities for future research directions and applications to agriculture, as well as highlight ongoing research at the University of Guelph, Guelph, Canada.

Agronomic Effectiveness of Cationic Phosphate Impurities Present in Superphosphate Fertilizers as Affected by Soil pH

The general concept that low‐water‐soluble phosphorus (P) fertilizers should be more agronomically effective when applied to acidic soils was developed based on sources containing mainly calcium (Ca)‐P compounds, but it may not hold true for sources with different chemical composition. To obtain information related to this issue, two important iron (Fe)–potassium (K)–P compounds present in superphosphates [Fe3KH8(PO4)6 · 6H2O, H8, and Fe3KH14(PO4)8 · 4H2O, H14] were prepared and characterized. These P sources were used to provide 30 and 60 mg P kg−1 as neutral ammonium citrate (NAC)+H2O‐soluble P. Reagent‐grade monocalcium phosphate (MCP) was used as a standard P source with high water solubility with an additional rate of 120 mg P kg−1 included. Also, mixtures of both Fe‐K‐P compounds and MCP were prepared to provide 0, 25, 50, 75, and 100% of the total P as MCP. All sources were applied to a clayey loamy acid soil (pH 5.3) classified as Rhodic Kanhapludult. The soil was incubated at two rates (0 and 10 g kg−1) of lime, which resulted in pH 5.4 and 6.8. Upland rice was cultivated to maturity. The H14 compound confirmed to be a highly effective source of P for the rice plants at both soil pH, as opposed to the H8, which was poorly effective when applied alone. When mixed with water‐soluble P (WSP), the H8 was able to provide P to the plants with the maximum yield of upland rice reached with 54.8 and 80.5% of WSP for pH 5.4 and 6.8, respectively. The high agronomic performance of the H14 compound clearly indicates that this low‐water‐soluble P source cannot be deemed as ineffective at high soil pH. Conducted with the financial support from the Research Foundation for the State of São Paulo (FAPESP).

Influence of Tithonia diversifolia and triple superphosphate on dissolution and effectiveness of phosphate rock in acidic soil

AbstractAn incubation and a pot experiment were conducted to evaluate the dissolution and agronomic effectiveness of a less reactive phosphate rock, Busumbu soft ore (BPR), in an Oxisol in Kenya. Resin (anion and anion + cation)‐extractable P and sequentially extracted P with 0.5 M NaHCO3, 0.1 M NaOH, and 1 M HCl were analyzed. Dissolution was determined from the increase in anion resin (AER)–, NaHCO3‐, and NaOH‐extractable P in soil amended with PR compared with the control soil. Where P was applied, resin P significantly increased above the no‐P treatment. Busumbu‐PR solubility was low and did not increase significantly in 16 weeks. Anion + cation (ACER)‐extractable P was generally greater than AER‐P. The difference was greater for PR than for triple superphosphate (TSP). The ACER extraction may be a better estimate of plant P availability, particularly when poorly soluble P sources are used. Addition of P fertilizers alone or in combination with Tithonia diversifolia (TSP, BPR, TSP + Tithonia, and BPR + Tithonia) increased the concentration of labile inorganic P pools (NaHCO3‐ and NaOH‐Pi). Cumulative evolved CO2 was significantly correlated with cumulative N mineralized from Tithonia (r, 0.51, p &lt; 0.05). Decrease in pH caused NH$ _4^+ $‐N accumulation while NO$ _3^- $‐N remained low where Tithonia was incorporated at all sampling times. However, when pH was increased, NH$ _4^+ $‐N declined with a corresponding rise in NO$ _3^- $‐N. Tithonia significantly depressed soil exchangeable acidity relative to control with time. A significant increase (p &lt; 0.05) was observed for P uptake but not dry‐mass production in maize where BPR was applied. The variations in yield and P uptake due to source and rates of application were statistically significant. At any given P rate, highest yields were obtained with Tithonia alone. Combination of Busumbu PR with TSP or Tithonia did not enhance the effectiveness of the PR. The poor dissolution and plant P uptake of BPR may be related to the high Fe content in the PR material.

Agronomic effects of multi-year surface-banding of dairy slurry on grass

Sleigh-foot application of slurry manure is the best method for applying slurry manure on many forage fields. This study was designed to assess agronomic effectiveness of multi-year surface banding of dairy slurry on a sward of tall fescue ( Festuca arundinacea Schreb.). Our study showed that with this application technology, crop recovery of total-N from applied manure in the long-term is only about 77% that of mineral fertilizer. Despite relative inefficiency of N uptake from manure, yield response to manure equaled that to fertilizer at equivalent total-N rates although N-recovery was significantly lower. About 26–32% of applied manure-N was stored in soil organic matter and the buildup of soil-N was related to application rate of organic N. At moderate applications rates (approx. 400 kg N ha −1 a −1), soil N accumulated at about 120 kg ha −1 annually compared to 98 kg ha −1 a −1 of unaccounted N, much of that probably volatilized and denitrified. Alternating between manure and fertilizer improved productivity per unit land area without increasing the rate of N non-recovery per unit of feed produced.

Effectiveness of phosphate fertilizers of diffrent water solubilities in relation to soil phophorus adsorption

Phosphate fertilizers should match soil attributes to enhance agronomic effectiveness and recovery by plants. The purpose of this study was to test the agronomic effectiveness of P sources varying in water solubility on two soils differing widely in P adsorption capacity (PAC). Soils selected for the study were Oxisols with very low available P and presenting low and high PAC (Ox-LPAC and Ox-HPAC, respectively). Both were limed to pH 5.4 in a greenhouse study conducted utilizing corn as the test crop. Treatments consisted of the two soils interacting with five P sources (monocalcium phosphate - MCP, low-grade single superphosphate - LG-SSP, multimagnesium phosphate - MMP, Arad phosphate rock - PR and a P impurity in triple superphosphate - H14), and four rates of P (12.5, 25.0, 50.0 and 100.0 mg kg-1). A control with no P was added for each soil. The treatments were arranged as blocks with three replicates. Plants were harvested 45 d after germination. Dry-matter yield and P uptake were measured and the relative agronomic effectiveness (RAE) compared with MCP as the standard. When applied in low rates of P (12.5 and 25.0 mg kg-1) the RAE of the alternative sources was higher in the soil with high PAC (45, 66, 39 and 65% in the Ox-HPAC for the LG-SSP, MMP, PR and H14, respectively, as opposed to 24, 40, 14 and 47% in the Ox-LPAC). Results suggest that sources of P with low water solubility can be agronomically more effective in soils with high PAC.

Agronomic effectiveness of biofertilizers with phosphate rock, sulphur and Acidithiobacillus for yam bean grown on a Brazilian tableland acidic soil

Phosphate rocks have low available P and soluble P fertilizers have been preferably used in plant crop production, although economic and effective P sources are needed. Experiments were carried out on a Brazilian Typic Fragiudult soil with low available P to evaluate the agronomic effectiveness of phosphate rock (PR) compared with soluble phosphate fertilizer. Yam bean ( Pachyrhizus erosus) inoculated with rhizobia (strains NFB 747 and NFB 748) or not inoculated was the test crop. Biofertilizers were produced in field furrows by mixing phosphate rock (PR) and sulphur inoculated with Acidithiobacillus (S+ Ac) in different rates (50, 100, 150 and 200 g S kg −1 PR), with 60 days of incubation. Treatments were carried out with PR; biofertilizers B 50, B 100, B 150, B 200; triple super phosphate (TSP); B 200 without Acidithiobacillus and a control treatment without P application (P 0). TSP and biofertilizers plus S inoculated with Acidithiobacillus increased plant growth. Soil acidity and available P increased when biofertilizers B 150 and B 200 were applied. We conclude that biofertilizers may be used as P source; however, long term use will reduce soil pH and potentially reduce crop growth.

Activity of phosphorus of synthetic Fe-K-P compounds in superphosphate fertilizers as affected by pH and ionic strength

The concentration of orthophosphate ions released from Fe-K-P compounds (Fe3KH8(PO4)6 .6H2O and Fe3KH14(PO4)8 .4H2O) present in superphosphates increases with pH, which initially suggests that the agronomic effectiveness of P fertilizers containing high amounts of these compounds would also increase with soil pH but studies considering activity, instead of concentration, are necessary. With this purpose, both compounds were synthesized under laboratory conditions, characterized by elemental chemical analysis, optical microscopy, X ray diffractometry, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), and used in a solubility study. Solutions of 0.01, 0.05 and 0.1 mol L-1 NaCl with pH adjusted to 3.0, 4.0, 5.0, 5.5, 6.0, 6.5, 7.0 and 7.5 were prepared for the solubility study of H8-syn, H14-syn and a phosphate rock (PR) from Brazil. The orthophosphate activity as H2PO4- and HPO4(2-) was calculated in each situation as related to pH and ionic strength using software MINTEQ. The remaining precipitates after equilibrium were chemically analyzed and subjected to X ray, SEM and EDS. Results of chemical analysis and instrumental techniques confirmed the preparation method. The activity of orthophosphate ions of both compounds tended to decrease under increasing pH and/or ionic strength of the solution, which in turn suggests that an increase in the solution pH does not necessarily promote an increase in the P bioavailability for plant uptake. This can be important when evaluating agronomic data of P fertilizers with high contents of these two Fe-K-P compounds.

Development and Validation of a Phosphate Rock Decision Support System

Although some mathematical models exist to assist in deciding whether or not to apply phosphate rock (PR) to soils as a source of P, these models focused either on the use of highly soluble PR sources, mainly for pastures, or were too impractical for field use. There was, therefore, a need to develop a Phosphate Rock Decision Support System (PRDSS) with more comprehensive capabilities to predict the relative agronomic effectiveness (RAE) of PR with respect to water‐soluble phosphorus (WSP) fertilizers at field and farm level. The PRDSS includes PR sources varying widely in solubility and different crop species grown on variable soil properties and rainfall conditions. In this paper, we describe the development and use of the mathematical model, PRDSS, to estimate RAE of PR sources with respect to WSP fertilizers and to calculate a simple index to be used for preliminary economic comparison of these two types of P sources. The PRDSS is able to function with a minimum input of only soil pH, the name of the mine that is the source of the phosphate rock, and the species of crop to be grown. A more accurate prediction of RAE is obtained from the PRDSS when more detailed data describing the soil, crop, and weather are included as inputs.

Combining Tithonia diversifolia and minjingu phosphate rock for improvement of P availability and maize grain yields on a chromic acrisol in Morogoro, Tanzania

A 2-year field experiment was conducted to evaluate the effects of Tithonia diversifolia green manure combined with either Minjingu phosphate rock (MPR) or triple super phosphate (TSP) on soil chemical properties that influence P availability, P pools and maize grain yields, on a Chromic Acrisol in Morogoro, Tanzania. Leafy biomass of tithonia was applied before maize planting for two consecutive growing seasons. Treatments compared were the control, MPR and TSP each at 80 kg P ha−1; tithonia alone at 2.5, 5.0, and 7.5 Mg ha−1 dry matter and tithonia combined with MPR or TSP at 40 kg P ha−1. Tithonia led to significant increases in soil pH, exchangeable Ca, labile (resin and NaHCO3-Pi), and moderately labile inorganic P (NaOH-Pi). It reduced exchangeable Al and P sorption. Application of MPR alone had liming effects and resulted in increase in labile P. Combining tithonia with MPR had similar but more intense effects. Triple superphosphate alone led to acidification and this was reversed when TSP was co-applied with tithonia. Increasing the application rates of tithonia either alone or in combination with TSP or MPR led to more pronounced liming effects but the differences between 2.5 and 5.0 Mg tithonia ha−1 were not significant due to moisture stress that was experienced during the season. The P and Ca concentrations of the maize plants at tasselling increased with the application of tithonia alone or combined with MPR or TSP, and were significantly correlated with maize grain yields (r = 0.75 and 0.64 for MPR and TSP, respectively). Tithonia added consecutively for 2 years increased total maize grain yields by 70% compared to that in the control. The relative agronomic effectiveness (RAE) of MPR increased from 46% in the first year of application to > 142% in the second year, indicating that the initially slow dissolution of MPR improved by combined application of tithonia and MPR, attributed to reduction of P sorption. It is concluded that tithonia can enhance P availability from the Chromic Acrisol through modification of soil properties associated with P transformation and availability. In cases where tithonia is found within the farmers’ fields its combined application with MPR can increase maize yields at a much-reduced cost associated with tithonia procurement.

OXYFERTIGATION: A NEW TECHNIQUE FOR SOILLESS CULTURE UNDER MEDITERRANEAN CONDITIONS

OXYFERTIGATION: A NEW TECHNIQUE FOR SOILLESS CULTURE UNDER MEDITERRANEAN CONDITIONS

Response of Field Beans (&lt;i&gt;Phaseolus vulgaris&lt;/i&gt; L.) to Unacidulated Phosphorus Source in an Andosols in Kenya

The agronomic effectiveness of minjingu rock phosphate (MRP) was compared with that of highly soluble phosphate triple superphosphate (TSP), in pot studies with field bean ( P. vulgaris L. ) in a greenhouse at the field station of Faculty of Agriculture, University of Nairobi, Kenya. MRP finely ground with 30 Grade % P and TSP with 99.6 Grade % P fertilizer at rates 0, 30, 45 and 60mg P pot -1 were applied on 2kg soil pot -1 . The soil used in the study was an acid humic andosol from fields with moribund tea bushes, tea bushes planted in 1958 and 1979 and newly cleared forest in Kagaa, Kenya. Shoot and root dry matter yields, dry seed yield responses and their response estimates were determined and showed positive significance in most cases when TSP fertilizer was applied on the soils except that from moribund tea field. The relative agronomic effectiveness (efficiency) of MRP on biomass and also seed yield of beans was found to be significantly inferior to TSP in most of the soils except that from moribund tea field where both sources were found to be ineffective. This study confirms that inspite of its high reactivity, MRP is still agronomically ineffective as nutrient source of Phosphorous for growing P. vulgaris in acid soils. Journal of Agriculture, Science and Technology Vol. 2 (1) 1999: 32-45

Hard Minjingu Phosphate Rock: an Alternative P Source for Maize Production on Acid Soils in Tanzania

The phosphate rock (PR) deposit at Minjingu in northern Tanzania consists of two forms, locally called hard Minjingu phosphate rock, MPR (4.8 × 106 Mg with 10.6% P) and soft MPR (3.3 × 106 Mg with 13.3% P). Extensive chemical and instrumental analyses have shown that the two MPRs differ mainly in consistency, while their reactivities are comparable. Soft MPR in direct application has been extensively evaluated with good results under greenhouse and field conditions whereas hard MPR has only been tested in a greenhouse experiment. The agronomic value of directly applied hard MPR on maize growth was therefore tested under field conditions on four acidic soils low in available Ca and P at Magadu (Ultisol), Mlingano (Oxisol), Nkundi (Ultisol) and Sasanda (Andisol). The treatments tested were hard MPR, soft MPR, triple superphosphate (TSP) and a control. Each P source was applied at a rate of 80 kg ha−1 P at Magadu, Mlingano and Nkundi but 160 kg ha−1 P at Sasanda. Other nutrient deficiencies were corrected in each soil with appropriate fertilizers that were applied in all three years of experimentation. The soils gave significant positive responses to application of the three P sources but TSP application resulted in significantly higher P concentrations in leaves and grain yields than MPR addition in the first year. However, in the second and third years the performance of MPRs approached that of TSP and the relative agronomic effectiveness (RAE) of MPRs increased from 50 – 70% in the first year to 80 – 95% in year three. Moreover, crop performances on hard MPR-treated plots and soft MPR-treated plots were not significantly different. This important result suggests that hard MPR can replace soft MPR and even TSP on acidic soils low in available Ca and P. However, more testing is needed to ensure confident delineation of soils that respond to direct application of hard MPR from non-responding soils. The rather poor performance of MPR for the first year must also be improved.

Biosolids effectiveness to yield ryegrass based on their nitrogen content

Biosolids have been reported to increase yields and supply plant nutrients. However, complying with health and environmental standards is necessary before applying biosolids to land. Thus, sludge stabilization is required to make biosolids safe enough for their agricultural use. Side effects of stabilization processes on agronomic features of sewage sludge are not quite known, although their understanding is essential for biosolids management. Based on a model equivalent to the Mitscherlich equation, effects of the most common processes for sludge stabilization were evaluated (composting, liming, heat-drying and solar irradiation) in relation to the agronomic effectiveness of biosolids to yield Lolium perenne L. on two tropical soils, with NH4H2PO4 as a reference. Sewage stabilization processes have affected the ability of biosolids to promote plant growth. Their effectiveness was usually higher than fertilizer in a Spodosol and lower in an Oxisol. Solar-irradiated sludge presented the highest effectiveness among the biosolids and reached peak yields at the lowest application rate independent on soil type. Biosolids could efficiently substitute fertilizers and even yield more plant dry matter than the NH4H2PO4 reference, depending on the biosolid and soil type.

Seletividade de herbicidas sobre as características de produção da cana-de-açúcar utilizando-se duas testemunhas

In Brazil studies of herbicides selectivity on the production parameters in sugar cane are generally carried out together with rehearsals of agronomic effectiveness in weeds and always using a checkplot per experimental replicate. When the contrast is analyzed considenry herbicide in relation to only one check without herbicide, there is a tendency in obtaining larger values for the variation coefficient, what could hide some effects of herbicides not selectives. Therefore, the objective of the present work, was specifically evaluate herbicide selectivity on sugarcane yield parameters: diameter, length, number of among knot and production of sugarcane stems, maintaining the portions constantly weeded, and using two lateral checks without herbicide adjacent to each treatment with herbicide. The results showed that in post-emergence, 2,4-D + hexazinone/ diuron (1.34 + 0.27/ 0.94 kg i.a./ there is) affected the diameter and the length of stems signifratinely, reducing the production in 16,6 t/ha. Tebuthiuron (0.96 kg i.a./ha) it affected the diameter, tebuthiuron + diuron (0.96 + 1.25 kg i.a./ha) and diuron + ametryn (1.25 kg i.a.l/ha) affected the number of among knot, reducing the stem production in 11.9; 17.0; 5.5 t/ha respectively. Ametryn (2.25 kg i.a./ha) and oxyfluorfen (0.72 kg i.a./ha) applied in pre-emergence they were not considered selective for the parameter number of among knot, however they didn't cause reduction in the stems production.

Iron Oxide-Impregnated Paper vs. Bray-1 Soil-Test Methods Predicting Crop Response from Phosphate-Rock Sources

The effectiveness of a Pi (iron oxide-impregnated paper) method was compared with that of Bray-1 method in extracting phosphorus (P) from an acid Hartsells silt loam (Typic Hapludult, pH 4.8) treated with low-release P fertilizers derived from Dorowa (Zimbabwe) phosphate rock (DPR) with maize (Zea mays L) as indicator crop in a randomized block design greenhouse experiment with three replicates. The fertilizers used were finely ground DPR, partially acidulated DPR (PADPR), a compacted mixture of DPR + triple superphosphate (TSP) + urea + potassium chloride (DTUK) with half of P from DPR and half from TSP, and a commercial grade single superphosphate (SSP) as a standard. The results indicated that the correlation between Bray-1 and Pi-extractable P was high (r = 97***). The regression coefficients for dry matter yield (DMY) and P uptake (PUPT) as a function of Bray-1 P level of SSP (DMY = 1.16 + 0.24Bray-1 P; PUPT = 0.93 + 0.45Bray-1 P) were significantly lower (p < 0.001) than those for DTUK (DMY = 1.16 + 0.43Bray-1 P; PUPT = 0.93 + 0.74Bray-1 P) and PADPR (DMY = 1.16 + 0.47Bray-1 P; PUPT = 0.93 + 0.82Bray-1 P). That is, a given soil-extractable P level with SSP resulted in a lower dry matter yield or P uptake than that from DTUK and PADPR. Thus, Bray-1 underestimated the agronomic effectiveness of DTUK and PADPR with respect to SSP. Based on this greenhouse research, soil testing for fertilizer recommendations using the Bray-1 test may result in two different response functions, one for water-soluble P sources and another for water-insoluble P sources.