Fertilizer and liming value of lime-treated sewage sludge

A field experiment was conducted with lucerne on a strongly acidic and phosphorus deficient soil to determine the liming and phosphorus and nitrogen fertilizer value of an undigested, lime-treated sewage sludge. The results are presented in terms of calculated combinations of lime, nitrogen and phosphorus fertilizer required to obtain the same lucerne yield (or soil pH or extractable phosphorus level) as achieved with 5 or 10 t ha^–1 of dried sludge.The sludge was a good source of lime, phosphorus and nitrogen. The sludge phosphorus was 49% as effective as the fertilizer phosphorus in raising extractable phosphorus in the soil to the level required for crop growth. The calcium carbonate of the sludge raised soil pH more effectively than agricultural lime, probably because of finer particle size in the former.It was not possible to achieve the yield obtained with 25 t ha^–1 of sludge with combinations of agricultural lime, and nitrogen and phosphorus fertilizers at high rates of application. This was attributed to the effects of the sludge on improving soil physical properties.     

Phosphorus management in continuous wheat and wheat-legume rotations

The sustainability of cropping systems is closely related to the judicious use of fertilizers. Little research has been conducted on the management of P in rotations in Morocco. The purpose of this study was to determine the effects of direct, cumulative, and residual P on wheat (Triticum aestivum) and chickpea (Cicer arietinum L.) yields under field conditions in two cropping systems: continuous wheat (W-W) and chickpea-wheat (CP-W). Experiments were conducted in 1994–96 at two locations in the arid and semiarid regions of Morocco. Phosphorus was applied the first year at rates of 0, 9, 18, and 27 kg P ha^–1 on both wheat and chickpea. The second year, plots were split into treatments with P and without P fertilizer. The changes in NaHCO₃-P in soil showed that after two years of cropping, P rates of 9 and 18 kg P ha^–1 were needed to increase and maintain soil test P level in the range where a third successive crop could be grown without fertilization at locations 1 and 2, respectively. Also, soils with the same initial NaHCO₃-P soil test levels required different amounts of fertilizer P to produce maximum yields. Inclusion of chickpea in the rotation resulted in a greater response to residual P by wheat at location 2. Differences in wheat grain yield between rotations were not significant. The maximum increase in yields above the nil-P treatment due to the highest amount applied in the the previous year was 1.3 t ha^–1, obtained for continuous wheat at location 2. Though the residual P effect was evident in this study, it did not produce maximum yields. Yields (GY, DM) could be predicted by the inclusion of both P applied in previous year (PR) and P applied in the current year (CP) by the following model: GY or DM = a + b*Ln(RP+1) + c*Ln(CP+1). Based on the range of P rates used in this study, a single P application for a 2-year rotation is not a suitable practice in these soils. The application of 18 kg P ha^–1 each year is recommended for continuous wheat, and 9 kg P ha^–1 the first year plus 18 kg P ha^–1 the second year is recommended for chickpea-wheat rotations. We suggest that either using single large applications of P or performing repeated applications should take into account the range of targeted application rates.     

Transformations of residual fertilizer P in a semi-arid tropical soil under eight-year peanut-wheat rotation

Long-term transformations of residual phosphorus (P) governs the availability of phosphorus to crops. Very limited information is available on the transformations of residual fertilizer P in semi-arid tropical soils under long-term crop rotations. Therefore, using sequential phosphorus fractionation procedure, we studied changes in labile and stable forms of inorganic and organic P in a semi-arid alluvial soil (Typic Ustisamments) after eight years of annual fertilizer P application either to one crop (alternate) or to both crops (cumulative) in a peanut (Arachis hypogaea) — wheat (Triticum aestivum) rotation.Total residual fertilizer P in soil (P recovered from P-fertilized minus control plots) ranged from 62 to 176 mg P kg^–1. In the alternate P treatments (P applied to peanut or wheat only), on an average of 3 rates of applied P (13, 26 and 39 kg P ha^–1), in surface (0–15 cm) and subsurface (15 to 30 cm) soil, respectively, residual fertilizer P consisted of 14.8 and 2.2% resin-P, 8.6 and 2.8% NaHCO₃-P, 6.3 and 0% microbial-P, 31.4 and 4.2% NaOH-P, 7.8 and 3.0% aggregate protected-P, 12.5 and 3.0% HCl-P, 3.4 and 0% H₂SO₄-P. The corresponding values for surface and subsurface soils of cumulative P treatments (P applied to both peanut and wheat) were: 12.8 and 1.6% resin-P, 6.9 and 2.3% NaHCO₃-P, 4.7 and 0% microbial-P, 32.5 and 4.2% NaOH-P, 5.6 and 2.0% aggregate protected-P, 14.8 and 3.8% HCl-P, 6.7 and 2.1% H₂SO₄-P. Considerable lower values for the 15–30 cm depth indicate only a very small movement of residual P to the subsoil.Significantly lower amount of fertilizer P (28% and 44%) found in labile (resin, NaHCO₃ and microbial P) and semi-labile (NaOH and sonicated NaOH P) fractions for the cumulative P treatment than alternate P treatment (35 and 46%, respectively) suggests that increased rates and frequency of applied P tend to enhance the conversion of residual P to stable forms which are less available to plants. About 12 to 19% of residual fertilizer P found as organic P in labile and semi-labile forms confirmed that organic P increased with long-term fertilizer management. In conclusion, the results of our study suggest that the alternate application of fertilizer P to a crop, as is shown for wheat, helps reduce the transformations of residual P to stable P forms.     

Maintenance of Phosphorus Fertilizer and Residual Phosphorus Effect on Corn Production

Phosphorus (P) deficiency is invariably a common crop growth and yield-limiting factor in unfertilized soils, especially soils high in calcium carbonate, which reduces P solubility. Even when such soils are fertilized, adsorption and desorption lead towards a reversion to stable and less soluble P forms, thus reducing fertilizer use efficiency. Field trials that examine the implications of such P reactions and residual fertilizer P responses in the field are relatively rare in Mediterranean environments. A 5-year field experiment in southern Turkey examined the residual effects of repeated P fertilizer applications for corn production in a calcareous soil Typic Xerofluvent. Following the initial year's fertilization (0, 33, 66 and 99 kg P ha⁻¹) to establish a range of soil P levels in subsequent years, the main plots received 0, 9, 18, 27 and 36 kg P ha⁻¹ annually. Grain P uptake was calculated for each year and used in the prediction of P recovery. All plots were sampled and analyzed for available P prior to planting with a local corn hybrid. Soil P values increased with the initial P levels (8–24 mg kg⁻¹) but declined after 3 years (6–10 mg kg⁻¹). Only the lowest annual P application rate (9 kg P ha⁻¹) produced an available P level that was not in the sufficiency range. Grain yields across the main and subplots and years ranged from 6.6 to 13.2 t ha⁻¹. Overall corn yield averaged over the years increased by 8–33% compared to the control as the rates of applied P increased. However, P application had no effect in a year when below-average rainfall restricted crop growth. A residual P effect on grain yield occurred with higher P application levels in the last year. Leaf and grain P concentrations were in the sufficiency range in general. Grain P uptake was calculated for each year and used in the prediction of P recovery. Actual recovery was higher with low P application rates and ranged between 10.8 and 46.4%. The study indicated that under irrigated conditions, corn is likely to respond to P fertilization, but that buildup of available P can occur within a few years and adequate plant available P levels can be maintained by modest P fertilizer application rates.     

Potential losses of fertilizer phosphorus by animal transfer

Pasture production, phosphorus (P) concentration, and P uptake by mixed pasture following addition in the autumn of 50 and 100 kgP ha^–1 as single superphosphate (SSP), triple superphosphate (TSP) and Sechura phosphate rock (SPR), and of 50 kgP ha^–1 of Chatham Rise phosphorite (CRP) were measured for one year on a Wainui silt loam (Typic Dystrochrept) and Tokomaru silt loam (Typic Fragiaqualf). A sharp increase was measured in the P concentration of mixed pasture immediately following the application of 50 and 100 kg P ha^–1 as either SSP or TSP at both sites. However, this increase was not accompanied by an increase in pasture production. In contrast, the application of 50 kgP ha^–1 as either SPR or CRP resulted in only small initial increases in the P concentration of mixed pasture, as did the addition of 100 kgP ha^–1 as SPR at both sites. The potential P losses by animal transfer in dung, which could result from the use of these four P fertilisers, were calculated using a P cycle constructed for intensively grazed, steep hill country pasture. Potential losses of fertilizer P, calculated as a percentage of fertilizer P added, were 7–14% for SSP and TSP, and 4–5% for SPR and CRP in the first year at the two sites. The implications of these results to the efficiency of P fertilizer use are discussed.     

Meat and bone meal as nitrogen and phosphorus fertilizer to cereals and rye grass

Meat and bone meal (MBM) contains appreciable amounts of total nitrogen (~8%), phosphorus (~5%) and calcium (~10%). It may therefore be a useful fertilizer for various crops. This paper shows results from both pot and field experiments on the N and P effects of MBM. In two field experiments with spring wheat, increasing amounts of MBM (500, 1000, 2000 kg MBM ha⁻¹) showed a linear yield increase related to the N-supply. A similar experiment with barley gave positive yield increase for 500 kg MBM ha⁻¹ and no further yield increase for larger amounts of MBM. Supply of extra mineral P gave no yield increase when 500 kg MBM ha⁻¹ or more was applied. Meat and bone meal as P fertilizer was studied in greenhouse experiments using spring barley and rye grass as test crops. N applications were 100 N kg ha⁻¹ to barley and 200 kg N ha⁻¹ to rye grass, either from mineral fertilizer or assuming that 80% of total N in MBM was effective. Four different P deficient soils were given increasing doses of MBM and compared with compound NPK fertilizer 11-5-18, mineral N fertilizer (0 kg P ha⁻¹) and a control (0 kg N ha⁻¹, 0 kg P ha⁻¹). In barley there was no significant yield difference between the NPK treatment and MBM treatment with equal N supply, and both had significant higher yield than the treatment receiving the same amount of mineral N without P-supply. The positive yield response of MBM was even larger in rye grass. Both in barley and rye grass a significant residual effect of P from MBM applied the year before was found when the treatments received the same amount of mineral N fertilizer (0 kg P ha⁻¹). The pot experiments confirmed the assumed N effect of MBM. When MBM is used according to the N demand of the crops, the P supply will be more than sufficient and residual P will be left in the soil. Since a part of this residual P was utilized by the crops of the following year, it is not recommended to apply P-fertilizer the year after MBM application.     

The initial and residual value for subterranean clover of phosphorus from crandallite rock phosphates,apatite rock phosphates and superphosphate

The residual value of phosphorus from superphosphate, crandallite rock phosphate (Christmas Island C-grade ore), 500°C calcined crandallite rock phosphate (Calciphos) and apatite rock phosphate from Queensland, Australia, was measured in a 6 year field experiment sited on lateritic soil in south-western Australia. Different amounts of each fertilizer were applied at the commencement of the experiment, and either left on the soil surface or mixed through the soil by cultivating to a depth of about 10 cm. Dry matter production of subterranean clover measured in spring (August) and bicarbonate-extractable phosphorus determined from soil samples collected in summer (January–February) were used as indicators of fertilizer effectiveness.The effectiveness values calculated for each fertilizer each year were similar for the treatments that were left on the soil surface and those which were mixed through the soil. The effectiveness of both ordinary and triple superphosphate were similar each year. They were the most effective fertilizers for the duration of the experiment. Using pasture yield as an indicator, the effectiveness of the superphosphates decreased by about 50% from year 1 to year 2, and by a further 10% over the remaining 4 years. Using bicarbonate-extracted soil phosphorus the effectiveness of both superphosphates decreased in a more uniform fashion by about 60% from year 2 to year 6. The effectiveness of all the rock phosphate fertilizers was approximately constant through time. As calculated from yield and bicarbonate-soluble phosphorus values, C-grade ore, Calciphos and the Queensland apatite were respectively 5%, 20% and 7% as effective as freshly applied superphosphate.The proportion of the total phosphorus content present in the rock phosphates which was initially soluble in neutral ammonium citrate was a poor predictor of the effectiveness of the phosphorus from these fertilizers determined using herbage yield or the amount of bicarbonate — soluble phosphorus extracted from the soil.The bicarbonate soil test did not predict the same future production for superphosphate and some of the rock phosphates in years 2 and 3 of the experiment, indicating that different soil test calibration curves are needed for the different fertilizers.     

The current and residual value of superphosphate,Christmas Island C-grade ore,and Calciphos as fertilizers for a subterranean clover pasture

The effectiveness in the year of application of three phosphorus fertilizers, superphosphate, Christmas Island C-grade ore, and 500°C calcined Christmas Island C-grade ore (Calciphos), was measured for 5 consecutive years in a field experiment on a lateritic soil. The residual value of the phosphorus fertilizers was also measured for 6 years. Dry matter production of subterranean clover-based pasture and bicarbonate extractable soil phosphorus were used as indicators of fertilizer effectiveness.Despite the use of very large amounts of C-grade ore and Calciphos, the plateau of the pasture yield versus fertilizer applied curve for these fertilizers did not reach the yield plateau achieved with superphosphate in either the short or long term.C-grade ore and Calciphos were 3% and 8% as effective as superphosphate for dry matter production in the year of application. Relative to superphosphate applied in the current year the effectiveness of superphosphate decreased by about 70% between the first and second year after application and decreased by a further 14% from year 3 to year 6. C-grade ore and Calciphos remained about 2% and 9% as effective as currently applied superphosphate each year.The residual value of superphosphate as measured by bicarbonate-extracted soil phosphorus decreased by about 60% from year 2 to year 7. The residual value of Calciphos was very low for year 2, doubled from year 2–4 and thereafter decreased gradually to its original value by year 7. The residual value of C-grade ore was extremely low throughout the experiment. Thus after year 2, compared to pasture yield, bicarbonate extracted soil phosphorus overestimated the residual value of superphosphate and calciphos.It follows that neither C-grade ore or Calciphos are suitable replacement fertilizers for superphosphate for use on pastures growing on lateritic soils in south-western Australia.     

Estimating nutrient surplus and nutrient use efficiency from farm characteristics

Research on nutrient losses from agricultural systems should try to relate these losses to farm characteristics. This was done for private farms in two districts in Poland. Using data from a farm survey, nutrient surpluses and Nutrient Use Efficiency (NUE, defined as the ratio of outgoing and incoming nutrients) were calculated for nitrogen and phosphorus. Both nutrient surplus and NUE are relatively high. A model was developed to estimate surpluses and NUE from farm characteristics like location, farm size, fertilizer application level, animal density, grass production and sugar beet or potato area. The results of the model are satisfying for nutrient surplus (R2=0.9) and nitrogen NUE (R2=0.4). Estimation of phosphorus NUE was not satisfactory. High surpluses are associated with high fertilizer applications, high animal density and high grass production while an increasing share of sugar beets leads to lower surpluses. A high nitrogen NUE is associated with low fertilizer applications, low animal density and little grass production, and with a high sugar beet area share. Results suggest that, with exception of sugar beet, fertilizer recovery in Poland is very low. Sugar beet, however, combines high fertilizer applications with low surpluses and high NUE. The outcome of the model can be used in the design of environmental policies. The paper ends with some remarks on the type of measures that can be taken, and the effects these will have on private farms in Poland.     

Evaluation of residual and cumulative phosphorus effects in contrasted Moroccan calcareous soils

Consideration of factors affecting the availability of applied P in soils could improve P fertilization recommendations. Little information is available on the effects of continuous P fertilizer applications under cropping systems in Morocco. A greenhouse study was conducted to evaluate the residual and cumulative P effects on three succeeding crops, wheat ( Triticum aestivum L.)-corn (Zea maize)-wheat, in contrasting calcareous soils from the arid and semiarid zones of Morocco. The treatments were the amount (0, 3.4, 6.7, or 13.4 mg P kg^-1 soil) and time of application of P. The residual P effects on grain yield, dry-matter production, and total P uptake were significant. In this study, the increase in yields as a function of applied P was explained by the model: Y = a + b*(P_ad)^0.5. The increase rate (constant b in the model) of dry-matter production of corn ranged from 0.56 (soil 10) to 2.89 (soil 11). At the same P fertilizer rate, single applications yielded less grain production than repeated applications. These results showed that if we want to take residual P into consideration in P fertilizer recommendations, the critical soil test P level should be lower than the one normally determined by soil test calibration method. Also, soils with low initial NaHCO₃-P levels had the lowest residual value, inferring that a large portion of added P is fixed in these soils. This study showed that a significant response of corn to residual P would occur in soils with initial NaHCO₃-P test levels less than 6 mg P kg^-1. The response would be inconsistent between 9 and 14 mg P kg^-1, and no response is expected above a soil test P level of 14 mg P kg^-1. In general, soils with more than 14 mg kg^-1 NaHCO₃-P could provide adequate P for maximum yield for three succeeding crops under greenhouse conditions.     

Effects of nitrogen and phosphorus fertilizers on unshaded Amazon cocoa in Nigeria

No extensive investigation on the effect of fertilizers on Amazon cocoa variety (Theobroma cacao L.) has been performed in Nigeria. Therefore eight fertilizer treatments involving nitrogen and phosphorus, replicated six times at four locations across southern Nigeria, were established in 1973. The four N levels (N0, N1, N2, N3) involved were 0, 80, 160 and 240 kg ha^–1 y^–1, and the two P levels (P₀, P₁) were 0 and 67 kg ha^–1 y^–1. Results of the first 5 years of fertilizer application are reported. Response to P was observed at all locations, and the response was statistically significant at 2 of the locations. There was no response to the application of nitrogen. The data suggest, however, that there is only a response to phosphorus when nitrogen is applied.     

Nitrogen fertilizer in leucaena alley cropping. II. residual value of nitrogen fertilizer and leucaena residues

Legume residues have been credited with supplying mineral nitrogen (N) to the associated cereal crop and improving soil fertility in the long term. Few studies using¹⁵N have reported the fate of legume N and fertilizer N in the presence of legume residues in soil-plant systems over periods of two years or longer. A field experiment was conducted in microplots to evaluate: (1) the residual value of the¹⁵N added in leucaena residues; (2) the residual value of fertilizer¹⁵N applied in the presence of unlabelled leucaena residues in the first year to maize over three subsequent years; and (3) the long-term fate of residual fertilizer and leucaena¹⁵N in a leucaena alley cropping system.There was a significant increase in maize production over three subsequent years after addition of leucaena residues. The residual effect of fertilizer N increased maize yield in the second year when N fertilizer was applied at 36 kg N ha^–1 in the first year in the presence of leucaena residues. Of the leucaena¹⁵N applied in the first year, the second, third and fourth maize crop recovered 2.6%, 1.8% and 1.4%, respectively. The corresponding values for the residual fertilizer¹⁵N were 0.7%, 0.4% and 0.3%. About 12–14% of the fertilizer¹⁵N added in the first year was found in the 200 cm soil profile over the following three years. This differed from the 38–41% of leucaena¹⁵N detected in the soil over the same period. Most of the residual fertilizer and leucaena¹⁵N in the soil was immobilized in the top 25 cm with less than 1% leached below 100 cm. More than 36% of the leucaena¹⁵N and fertilizer¹⁵N added in the first year was apparently lost from the soil-plant system in the first two years. No further loss of the residual leucaena and fertilizer¹⁵N was detected after two years.     

Phosphorus bioavailability of fertilizers: A predictive laboratory method for its evaluation

A laboratory method and a laboratory index is proposed to estimate the phosphorus taken up by plants that is derived from fertilizers (Pdff). Pdff values were measured using greenhouse experiments and³²P labelling technics. The laboratory index estimates the proportion of PO₄-ions derived from the fertilizer in the soil solution and is measured by means of an isotopic exchange of³²PO₄-ion procedure. This indicator was named JCF. Two typical soil-fertilizer conditions were studied. One concerned measurement of Pdff and JCF values for freshly-applied phosphorus as diammonium phosphate (DAP) at levels of 15, 30, 45, 60 and 90 mg P kg^–1 soil. The other concerned measures of Pdff and JCF values for two types of P residues previously applied in soils as concentrated superphosphate (CSP) or Gafsa rock phosphate (GRP) applied at 0 and 43.7 kg.ha^–1 each year over a 15 yr period.For freshly-applied DAP a linear relationship between Pdff and JCF values was obtained over the range of 0 to 90 mg P (kg soil)^–1 levels of application: JCF = 1.16 Pdff + 1.78, (r ² = 0.98). For the P residues, JCF and Pdff values were not significantly different for a given residual treatment. However JCF and Pdff pair data for CSP treatments (56.0, 65.9) were about tenfold superior to those for GRP treatments (5.3, 4.6)). Consequently the nearly 1:1 ratio between JCF and Pdff values that was obtained for the two different soil-fertilizer conditions suggests that the proposed laboratory method can be used to predict availability of P fertilizers to plants. Thus it deserves to be considered in helping to estimate P fertilizer applications.     

The effect of nitrogen,phosphorus and potassium fertilizer applications on the seed yield of sunflower (Helianthus annuus L.) grown on sandy soils and the prediction of phosphorus and potassium responses by soil tests

The nitrogen, phosphorus and potassium requirement of sunflower was evaluated when the crop was grown on siliceous sands overlying clay in the south east of South Australia. Of the seven sites used in the investigation, significant seed yield responses to phosphorus were recorded at two, while at a further two sites seed yields were increased by potassium additions. Nitrogen applications did not significantly increase seed yields at any site but decreased seed yields at two. This lack of nitrogen response was attributed to the sites having been long term legume pastures prior to the sunflower crops.Oil concentrations of sunflower seed ranged from 40.6% to 45.3% between sites, but fertilizer treatment had no significant effect.Critical nutrient ranges for both soil (Colwell) extractable phosphorus and potassium were derived at maximum seed yield. These were 16–20 mg kg^–1 for extractable phosphorus and 70–80 mg kg^–1 for extractable potassium.     

The balance sheet approach to determination of phosphate maintenance requirements

A balance sheet model has been used to calculate the efficiency of phosphorus applied at stable levels of pasture production. This shows that P is used efficiently, with 70 to 90% of fertilizer and recycled P being utilized by plants. The remaining P not used by plants (10 to 30%) is lost due to chemical reactions or downward movement in the soil. Utilization efficiency declines as the maximum yield (in respect to P nutrition) is approached on any soil.The fertilizer phosphate maintenance requirements of grasslands can be calculated on the basis of the efficiency of P utilization by pasture plants and the amount of P recycled in plant and animal residues at any stable P output, i.e. steady state. The amount of recycled P has been obtained by deducting from P uptake the amount of P removed in produce and lost by transfer under (a) dairy farming, and (b) cattle and sheep farming.In this paper the phosphate maintenance requirements have been calculated for soils of low, medium and high production potential, each at 70 and 85% utilization at 90% of maximum production.     

Africa — how much fertilizer needed: Case study of Sierra Leone

The quantities of nitrogen, phosphorus and potassium supplied by an average African soil cleared from bush fallow, assuming no losses, were approximated. Values ranged from 23 to 120 Kg N ha^–1, 1.8 to 12 Kg P ha^–1, 47 to 187 Kg K ha^–1, depending on type of fallow, length of fallow, drainage and extent of depletion of native supplies. Additional amounts of 4 to 5 Kg N ha^–1, 4 to 6 Kg P ha^–1 and 14 to 20 Kg K ha^–1 are obtained from the ash.Using crop nutrient removal data and approximate efficiencies of native and fertilizer N, P and K, fertilizer requirements at the reconnaissance level were estimated for selected target yields. For newly cleared uplands at cropping/fallow ratio of 2:7, N fertilizer requirements for cassava (30 t ha^–1), maize (4 t ha^–1), and sweet potato (16 t ha^–1), were 138, 98, 42 kg ha^–1 respectively. Wetland rice (4 t ha^–1) required 55 kg N ha^–1. Corresponding P fertilizer requirements for cassava, maize, sweet potato, upland rice (1.5 t ha^–1) and ground-nut (1 t ha^–1) were 190, 80, 30, 30 and 16 kg P ha^–1 respectively. Wetland rice required 83 kg P ha^–1. Substantial residual values of applied P are to be expected. Cassava required 60 kg ha^–1 of K on newly cleared land. In soils of lowered nutrient status higher N, P, and K fertilizer requirements were indicated for all crops.Land use data from Sierra Leone were used to illustrate how the total quantities of N, P and K fertilizers in a country in the forest zone of Africa can be approximated. Fertilizer needs in Sierra Leone were in decreasing order P > N K. N, P and K requirements were estimated to be 10,000 t, 20,000 t and 4,000 t respectively. The nutrient balance sheet method described in this paper is a useful tool to estimate the order of magnitude of fertilizer requirement at selected target yields for countries in Africa.     

磷缓释复混肥的制备及其氮、磷缓释性评价

在实验室条件下制得不同程度磷缓释的复混肥(磷缓释肥),分别测定以水为淋洗剂和以2%柠檬酸溶液为淋洗剂时在特定淋洗装置下水溶性氮、磷及有效磷随时间的溶出率,采用双曲线方程Xt=b a/t对肥料的累计养分溶出率进行分段拟合,在此基础上引入缓释指数评价各养分缓释特性。结果表明:磷缓释肥对磷的缓释作用强于氮,对有效性磷的缓释作用强于水溶性磷;其水溶性氮、磷缓释指数(SR IWN、SR IW P)和有效磷缓释指数(SR IAP)与肥料中加入的缓释剂硫酸镁相对含量(X)具有很好的正相关,其直线相关系数为0.7414、0.8958和0.9829,后两者分别达到显著和极显著水平;2%柠檬酸溶液几乎能溶出肥料中全部有效磷,从而证明了自制磷缓释肥的有效性。     

Assessment of economically optimum application rates of fertilizer N on the basis of response curves

N-response curves of numerous N-fertilizer trials with sugar beet and potato are described by a quadratic and a modified exponential equation. For both sugar beet and potato the modified exponential equation was much better than the quadratic equation when the residual sum of squares (RSS) was taken as a measure of the degree of fit. In order to take into account the few occasions when the quadratic model was superior, it is suggested that both models should be used for the data of each individual trial. The economically optimum application rate of fertilizer N is calculated on the basis of the best-fitting model. This procedure yielded optima which covered entire ranges of fertilizer-N levels tested: 0–250 kg ha^–1 for sugar beet and 0–400 kg ha^–1 for potato. The magnitude of the confidence intervals (p > 95%) of the optimum N-fertilizer application rate frequently was very high. In 46% of the sugar beet trials and even in 60% of the potato trials it was higher than 300 kg ha^–1 N. It is suggested that N-fertilizer recommendations be drawn up only with reliable optima.     

A farm-level evaluation of nitrogen and phosphorus fertilizer use and planting density for pearl millet production in Niger

Mineral fertilizer use is increasing in West Africa though little information is available on yield response in farmers' fields. Farmers in this region plant at low density (average 5,000 pockets ha^–1, 3 plants pocket^–1), which can affect fertilizer use efficiency. A study was conducted with 20 farmers in Niger to assess the response of pearl millet [Pennisetum glaucum (L.) R. Br.] to phosphorus and nitrogen fertilizers under farm conditions. In each field, treatments included control, single superphosphate (SSP) only, SSP plus N (point placed near plant), and either SSP or partially acidulated phosphate rock (PAPR) plus N broadcast. N and P were applied at 30 kg N ha^–1 and 30 kg P₂O₅ ha^–1. Farmers were allowed to plant, weed, etc., as they wished and they planted at densities ranging from 2,000 to 12,000 pockets ha^–1. In the absence of fertilizer, increasing density from 2,000 to 7,000 pockets ha^–1 increased yield by 400%. A strong interaction was found between fertilizer use and density. Farmers planting at densities less than 3,500 pockets ha^–1 had average yields of 317 kg grain ha^–1 while those planting at densities higher than 6,500 pockets ha^–1 showed average yields of 977 grain ha^–1. Though phosphate alone increased yields significantly at all densities, little response to fertilizer N was found at densities below 6,000 pockets ha^–1. Significant residual responses in 1987 and 1988 were found to P applied in high-density plots in 1986. Depending on fertilizer and grain prices, analysis showed that fertilizer use must be be combined with high plant density (10,000 pockets ha^–1) or no economic benefit from fertilizer use will be realized.