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This literature review on mineral nutrition of cocoa was commissioned by the Scientific Committee of the Cocoa Fertiliser Initiative to address the following questions: What knowledge is currently available about mineral nutrition of cocoa? What are the current knowledge gaps? What are the key areas for further research?

This literature review on mineral nutrition of cocoa was commissioned by the Scientific Committee of the Cocoa Fertiliser Initiative to address the following questions: What knowledge is currently available about mineral nutrition of cocoa? What are the current knowledge gaps? What are the key areas for further research?

Key words: Nitrogen, phosphorus, food chain, food pyramid, food system, food security, food cost, environmental impacts, nutrient cycling, nutrient management Nitrogen (N) and phosphorus (P) fertilizer applications have greatly contributed to the increased global food production during the last decades, but have also contributed to decreasing N and P use efficiencies (NUE and PUE) in the food production - consumption chain, and to increased N and P losses to air and water, with major ecological implications. The aim of this thesis is to increase the quantitative understanding of N and P flows and losses in the food production - consumption chain in China at regional level in the past 30 years and to develop strategies to increase NUE and PUE in the food chain. A novel ‘food chain’ approach and the NUFER model were developed to analyse N and P flows in crop production, animal production, food processing and retail, and households. Data were derived from statistical sources, literature and field surveys. Between 1980 and 2005, NUE and PUE decreased in crop production, increased in the animal production and decreased in the whole food chain. Total N losses to water and atmosphere almost tripled between 1980 (14.3 Tg) and 2005 (42.8 Tg), and P losses to water systems increased from 0.5 to 3.0 Tg. There were significant regional differences in NUE, PUE, and N and P losses; regions with high N and P losses were in Beijing and Tianjin metropolitans, Pearl River Delta, and Yangzi River Delta. Urban expansion is a major driving force for change; total N losses increased 2.9 folds, and P losses increased even 37 folds during the development of Beijing metropolitan, between 1978 and 2008. Scenario analyses indicated that implementation of a package of integrated nutrient management measures, combined with diet changes and increased imports of animal food and feed, are the most effective management options for increasing NUE and PUE, and for decreasing N and P losses. Application of the food chain approach and the NUFER model can help policy makers in China to plan food production - consumption chains, and thereby manage N and P flows in this chain at regional level.

The national phosphorus balance can be made more sustainable by reducing the accumulation of phosphorus in agricultural soils and by increasing recycling from waste streams. This study investigated different scenarios for reduction of the national soil surplus on agricultural land. The focus was on scenarios that will not compel agriculture in the Netherlands to change radically e.g. reduction of phosphorus fertilisation levels and reducing animal phosphorus excretion by improving feeding efficiency while maintaining national milk and meat production levels.

The national phosphorus balance can be made more sustainable by reducing the accumulation of phosphorus in agricultural soils and by increasing recycling from waste streams. This study investigated different scenarios for reduction of the national soil surplus on agricultural land. The focus was on scenarios that will not compel agriculture in the Netherlands to change radically e.g. reduction of phosphorus fertilisation levels and reducing animal phosphorus excretion by improving feeding efficiency while maintaining national milk and meat production levels.

Het overdadig gebruik van (kunst)mest heeft geleid, en leidt nog steeds, tot milieuproblemen voor oppervlakte- en grondwater. Gevolg hiervan is een groeiende behoefte, alsmede een steeds stringenter mestbeleid, om bemestingsadviezen te optimaliseren waarbij zowel de gewasopbrengst als milieudoelstellingen worden verenigd. Om deze optimalisatie te bereiken is het belangrijk de gekozen meetmethodes en de interpretatie van de resultaten die dat oplevert, beter te onderbouwen. Deze dissertatie presenteert resultaten van onderzoek dat zich richt op de vergroting van het inzicht in de chemische processen die de beschikbaarheid van fosfaat (P) en kalium (K) in de bodem bepalen. Deze inzichten zijn vervolgens gebruikt om een combinatie van standaard bodem meetmethodes af te leiden die in routinelaboratoria gebruikt kunnen worden.

Het overdadig gebruik van (kunst)mest heeft geleid, en leidt nog steeds, tot milieuproblemen voor oppervlakte- en grondwater. Gevolg hiervan is een groeiende behoefte, alsmede een steeds stringenter mestbeleid, om bemestingsadviezen te optimaliseren waarbij zowel de gewasopbrengst als milieudoelstellingen worden verenigd. Om deze optimalisatie te bereiken is het belangrijk de gekozen meetmethodes en de interpretatie van de resultaten die dat oplevert, beter te onderbouwen. Deze dissertatie presenteert resultaten van onderzoek dat zich richt op de vergroting van het inzicht in de chemische processen die de beschikbaarheid van fosfaat (P) en kalium (K) in de bodem bepalen. Deze inzichten zijn vervolgens gebruikt om een combinatie van standaard bodem meetmethodes af te leiden die in routinelaboratoria gebruikt kunnen worden.

Verlaging (kunstmest)fosfaatgebruik op het Lagekostenbedrijf leidt tot een P-Al daling, die bijnormaal gebruik maar net kan worden aangevuld. Bij herinzaai daalt de P-AL sterk en kan bij demestwetgeving van 2009 niet meer worden aangevuld.

Verlaging (kunstmest)fosfaatgebruik op het Lagekostenbedrijf leidt tot een P-Al daling, die bijnormaal gebruik maar net kan worden aangevuld. Bij herinzaai daalt de P-AL sterk en kan bij demestwetgeving van 2009 niet meer worden aangevuld.

Crop yields in Tanzania are often limited by P deficiency. Direct application of the locally mined Minjingu phosphate rock (MPR) is considered a possible option in addressing the problem. Being poorly soluble, it is more effective in low pH soils with sizeable P and Ca sinks. In soils rather high in pH, mechanisms are required to promote its dissolution. This research was initiated with the overall objective of increasing our understanding of the multiple interactions affecting the availability of P from MPR in the soil-plant system. This knowledge is required to enable optimal exploitation of the various factors influencing MPR effectiveness for increased crop production. The research program consisted of one laboratory experiment, six greenhouse experiments and four field trials.The laboratory and greenhouse experiments dealt with single factors influencing the effectiveness of PR under controlled conditions. From the laboratory experiment it was established that the high content of CaCO 3 in Minjingu PR was the major factor that determined the amount of HCl extractable P. However, agronomically it did not differ from Khouribga and Mali PRs, which have relatively lower CaCO 3 content. High application rates lowered the effectiveness of PR pointing to a need to balance application rates with proton supply. In a study relating yield and soil pH, increasing dry-matter yield of maize, cowpea and pigeonpea could not noticeably affect the soil pH mainly due to the pH buffer capacity of the soils. However, when intercropped with maize, cowpea or pigeonpea took up more P from MPR and even improved the uptake of MPR-P by maize. This point to a possible proton induced dissolution of MPR by the legumes. Hence, when intercropping involves legume crops capable of fixing N lower rates of PR can be used which is an attractive option for resource poor farmers. A study on the response of maize, cowpea and pigeonpea to MPR and TSP on soils of low and high pH showed that response to MPR was stronger in the low than in the high pH soil. Both legumes gave a higher DM production with MPR than with TSP on the high pH soil and yields were higher on the high than on the low pH soil. This indicates that the legumes prefer a high soil pH to a low soil pH and are able to make use of MPR at a relatively high pH. The later is possible when the legumes can modify rhizosphere soil conditions with respect to pH.Maize dry-matter yield response to P on soils with different pH and available P was observed where soil available P was low. There was no yield response to P when P-Bray-I was > 7 mg kg -1 (P-Olsen > 10 mg kg -1 ). Utilization of absorbed P was better from MPR than from TSP in low pH soils indicating a liming effect by the MPR.Field experiments dealt with multiple factors influencing the effectiveness of PR. The influence of spatial soil variability on the effectiveness of PR and crop performance was studied using the Post-mortem Residual Analysis and Nearest Neighbor Means techniques. These techniques were effective in isolating environmental from treatment effects and they were more useful in the large than in the small trials. A study on the method and rate of P application showed that method of application was more important for MPR in high pH soils and that response to MPR will be obtained at modest rates. The residual effects of TSP and MPR were almost the same. Combined application of MPR and the acidifying fertilizer sulfate of ammonia showed that there is little scope for improving the effectiveness of MPR through the acidifying effect of sulfate of ammonia. Combined application of MPR and TSP gave best results in low pH soils when both of them were applied using the same method. Meanwhile, incubating MPR with farmyard manure could not stimulate MPR dissolution given the high pH of the two materials even after 40 days of incubation (pH (H 2 O) = 8.35). It is concluded that the use of MPR could be extended to less acidic P deficient soils when mechanisms are employed that could stimulate its dissolution. They include use of low amounts of MPR (low input strategy), incorporating legumes in the cropping system and using the same method of application of mixtures of MPR and soluble P fertilizers.Keywords: Minjingu phosphate rock, triple superphosphate, Rhodic Ferralsols, farmyard-manure, protons, dissolution, legumes, maize, management options, spatial soil variability, Tanzania.

Crop yields in Tanzania are often limited by P deficiency. Direct application of the locally mined Minjingu phosphate rock (MPR) is considered a possible option in addressing the problem. Being poorly soluble, it is more effective in low pH soils with sizeable P and Ca sinks. In soils rather high in pH, mechanisms are required to promote its dissolution. This research was initiated with the overall objective of increasing our understanding of the multiple interactions affecting the availability of P from MPR in the soil-plant system. This knowledge is required to enable optimal exploitation of the various factors influencing MPR effectiveness for increased crop production. The research program consisted of one laboratory experiment, six greenhouse experiments and four field trials.The laboratory and greenhouse experiments dealt with single factors influencing the effectiveness of PR under controlled conditions. From the laboratory experiment it was established that the high content of CaCO 3 in Minjingu PR was the major factor that determined the amount of HCl extractable P. However, agronomically it did not differ from Khouribga and Mali PRs, which have relatively lower CaCO 3 content. High application rates lowered the effectiveness of PR pointing to a need to balance application rates with proton supply. In a study relating yield and soil pH, increasing dry-matter yield of maize, cowpea and pigeonpea could not noticeably affect the soil pH mainly due to the pH buffer capacity of the soils. However, when intercropped with maize, cowpea or pigeonpea took up more P from MPR and even improved the uptake of MPR-P by maize. This point to a possible proton induced dissolution of MPR by the legumes. Hence, when intercropping involves legume crops capable of fixing N lower rates of PR can be used which is an attractive option for resource poor farmers. A study on the response of maize, cowpea and pigeonpea to MPR and TSP on soils of low and high pH showed that response to MPR was stronger in the low than in the high pH soil. Both legumes gave a higher DM production with MPR than with TSP on the high pH soil and yields were higher on the high than on the low pH soil. This indicates that the legumes prefer a high soil pH to a low soil pH and are able to make use of MPR at a relatively high pH. The later is possible when the legumes can modify rhizosphere soil conditions with respect to pH.Maize dry-matter yield response to P on soils with different pH and available P was observed where soil available P was low. There was no yield response to P when P-Bray-I was > 7 mg kg -1 (P-Olsen > 10 mg kg -1 ). Utilization of absorbed P was better from MPR than from TSP in low pH soils indicating a liming effect by the MPR.Field experiments dealt with multiple factors influencing the effectiveness of PR. The influence of spatial soil variability on the effectiveness of PR and crop performance was studied using the Post-mortem Residual Analysis and Nearest Neighbor Means techniques. These techniques were effective in isolating environmental from treatment effects and they were more useful in the large than in the small trials. A study on the method and rate of P application showed that method of application was more important for MPR in high pH soils and that response to MPR will be obtained at modest rates. The residual effects of TSP and MPR were almost the same. Combined application of MPR and the acidifying fertilizer sulfate of ammonia showed that there is little scope for improving the effectiveness of MPR through the acidifying effect of sulfate of ammonia. Combined application of MPR and TSP gave best results in low pH soils when both of them were applied using the same method. Meanwhile, incubating MPR with farmyard manure could not stimulate MPR dissolution given the high pH of the two materials even after 40 days of incubation (pH (H 2 O) = 8.35). It is concluded that the use of MPR could be extended to less acidic P deficient soils when mechanisms are employed that could stimulate its dissolution. They include use of low amounts of MPR (low input strategy), incorporating legumes in the cropping system and using the same method of application of mixtures of MPR and soluble P fertilizers.Keywords: Minjingu phosphate rock, triple superphosphate, Rhodic Ferralsols, farmyard-manure, protons, dissolution, legumes, maize, management options, spatial soil variability, Tanzania.

A study is presented on the adsorption of phosphate on goethite, the interaction of phosphate with other adsorbing ions at the goethite surface, and the resulting availability of phosphate to plants. The plant-availability of sorbed phosphate was determined from phosphorus uptake of plants growing on an artificial substrate containing goethite with phosphate. Uptake can be predicted from zero sink behaviour of a growing root system, diffusion and mass flow in soil, and measured non linear adsorption of phosphate on goethite. With high phosphate loading of goethite, the equilibrium phosphate concentration in solution increased, which resulted in larger phosphate availability. Competitive interaction between phosphate and sulphate on goethite caused only a small decrease in phosphate adsorption at low pH, where sulphate adsorption is strongest, but a considerable increase in the phosphate concentration in solution.Experiments showed that phosphorus uptake by plants growing on suspensions of goethite in the presence of sulphate was seven times larger at pH 3.7 than at pH 5.5. Citrate competes more strongly with phosphate than sulphate, and shows strongest interaction at pH 4.5-5. On account of the non-linear adsorption behaviour of phosphate, the relative increase in phosphate in solution upon competition is much larger at low than at high phosphate loading of goethite. Therefore, competition results in an apparent lower affinity of phosphate sorption on goethite.Adsorption of the individual anions and competitive adsorption was described with the CD-MUSIC ion adsorption model, which is based on a detailed description of the adsorbing surface and the use of surface complexes identified in spectroscopic studies. The combination of the ion adsorption model with the uptake model is a powerful tool to predict the phosphate availability to plants. This was illustrated with a simulation study in which the effect of citrate exudation from roots on the uptake of phosphate was predicted.

A study is presented on the adsorption of phosphate on goethite, the interaction of phosphate with other adsorbing ions at the goethite surface, and the resulting availability of phosphate to plants. The plant-availability of sorbed phosphate was determined from phosphorus uptake of plants growing on an artificial substrate containing goethite with phosphate. Uptake can be predicted from zero sink behaviour of a growing root system, diffusion and mass flow in soil, and measured non linear adsorption of phosphate on goethite. With high phosphate loading of goethite, the equilibrium phosphate concentration in solution increased, which resulted in larger phosphate availability. Competitive interaction between phosphate and sulphate on goethite caused only a small decrease in phosphate adsorption at low pH, where sulphate adsorption is strongest, but a considerable increase in the phosphate concentration in solution.Experiments showed that phosphorus uptake by plants growing on suspensions of goethite in the presence of sulphate was seven times larger at pH 3.7 than at pH 5.5. Citrate competes more strongly with phosphate than sulphate, and shows strongest interaction at pH 4.5-5. On account of the non-linear adsorption behaviour of phosphate, the relative increase in phosphate in solution upon competition is much larger at low than at high phosphate loading of goethite. Therefore, competition results in an apparent lower affinity of phosphate sorption on goethite.Adsorption of the individual anions and competitive adsorption was described with the CD-MUSIC ion adsorption model, which is based on a detailed description of the adsorbing surface and the use of surface complexes identified in spectroscopic studies. The combination of the ion adsorption model with the uptake model is a powerful tool to predict the phosphate availability to plants. This was illustrated with a simulation study in which the effect of citrate exudation from roots on the uptake of phosphate was predicted.

In tropical soils, plant growth is often limited by a low P availability. In addition, these soils often have high P-fixation capacities due to high amounts of iron and aluminum oxyhydroxides. Furthermore, small-scale farming systems in which subsistence crops are produced for local markets are common in the tropics. Such conditions exit in South West Kenya, in the Kish area, where this study was carried out.The overall aim of the study was to improve our understanding of fertilizer P - soil - maize crop interactions and, thereby, to increase the yield response and improve the P recovery and utilization in plants. Initial and residual yield responses to fertilizer P applications; P uptake in plants, as well as P distribution and utilization within the plants; apparent fertilizer P recovery; and dissolution, transport and sorption of fertilizer P in the soils were studied under field conditions during three successive growing seasons. This was done within the concept of the low-input strategy, whereby the high-input strategy was used as a reference.The soils were classified as Ultisols and Mollisols, or as Nitisols and Luvic Phaeozems. They were low in available native P (P-Olsen 1.6 to 3.2 mg/kg) and had medium to high P sorption capacities (445 to 870 mg/kg) measured under laboratory conditions. Total P ranged from 490 to 1,035 mg/kg. Triple superphosphate was used as P fertilizer and hybrid maize as test crop.Good initial and residual yield responses were found in all soils even at low P application rates. The concept of P-fixation, as defined in this study, was not appropriate for the soils in the Kisii area. The second 'slow' phase of the fixation process was shown to proceed at a very slow rate under field conditions. Thus, P fixation is much less of a problem for farmers than expected. When P limited grain yield, the relationship between grain yield (z) and P in plant (y) could be described by the equation: z=620(y-0.50). The efficiency of utilization increased with P application to about 550 kg/kg at P rates of 22 to 131 kg/ha and decreased at higher rates due to a luxurious P uptake. Granular fertilizer residues with P in the form of Fluorapatite, Brushite and an amorphous P compound could be recovered in the soil until the end of the trials, about 600 days after application. Fertilizer P was retained in the soil immediately surrounding the residual fertilizer granules to total P values up to>8,000 mg/kg, which was much higher than predicted from the P-sorption studies in the laboratory. Available P levels (P-Olsen) in the P-enriched soil volume were high, up to>800 mg/kg. The available fertilizer P fraction (ΔP-Olsen/ΔP total) remained fairly constant with time. It was suggested that the number of roots, i.e. root surface area, present in the small P-enriched volume was the limiting factor in fertilizer P uptake. As a result, the apparent P recoveries per crop were low. They were about 10 % each growing season at a P rate of 22 kg/ha.Subseed placement at the start of each growing season is recommended, either placed alone or together with small amounts of cow dung. Then, plants benefit highly from both the startereffect of freshly-applied fertilizer and the residual effect of previously-applied (residual) fertilizer. P application rates of 20 to 40 kg/ha (in P 2 O 5 : 45 to 90 kg/ha) are advised for maize. At these rates, slightly more P is applied than plants require for producing maximum grain yields and the P availability of the soils will gradually increase by enlarging the soil volume enriched with fertilizer P. This repeated subseed placement fits in well with the low-input strategy and is probably easily adaptable in tropical small-scale farming systems.

In tropical soils, plant growth is often limited by a low P availability. In addition, these soils often have high P-fixation capacities due to high amounts of iron and aluminum oxyhydroxides. Furthermore, small-scale farming systems in which subsistence crops are produced for local markets are common in the tropics. Such conditions exit in South West Kenya, in the Kish area, where this study was carried out.The overall aim of the study was to improve our understanding of fertilizer P - soil - maize crop interactions and, thereby, to increase the yield response and improve the P recovery and utilization in plants. Initial and residual yield responses to fertilizer P applications; P uptake in plants, as well as P distribution and utilization within the plants; apparent fertilizer P recovery; and dissolution, transport and sorption of fertilizer P in the soils were studied under field conditions during three successive growing seasons. This was done within the concept of the low-input strategy, whereby the high-input strategy was used as a reference.The soils were classified as Ultisols and Mollisols, or as Nitisols and Luvic Phaeozems. They were low in available native P (P-Olsen 1.6 to 3.2 mg/kg) and had medium to high P sorption capacities (445 to 870 mg/kg) measured under laboratory conditions. Total P ranged from 490 to 1,035 mg/kg. Triple superphosphate was used as P fertilizer and hybrid maize as test crop.Good initial and residual yield responses were found in all soils even at low P application rates. The concept of P-fixation, as defined in this study, was not appropriate for the soils in the Kisii area. The second 'slow' phase of the fixation process was shown to proceed at a very slow rate under field conditions. Thus, P fixation is much less of a problem for farmers than expected. When P limited grain yield, the relationship between grain yield (z) and P in plant (y) could be described by the equation: z=620(y-0.50). The efficiency of utilization increased with P application to about 550 kg/kg at P rates of 22 to 131 kg/ha and decreased at higher rates due to a luxurious P uptake. Granular fertilizer residues with P in the form of Fluorapatite, Brushite and an amorphous P compound could be recovered in the soil until the end of the trials, about 600 days after application. Fertilizer P was retained in the soil immediately surrounding the residual fertilizer granules to total P values up to>8,000 mg/kg, which was much higher than predicted from the P-sorption studies in the laboratory. Available P levels (P-Olsen) in the P-enriched soil volume were high, up to>800 mg/kg. The available fertilizer P fraction (ΔP-Olsen/ΔP total) remained fairly constant with time. It was suggested that the number of roots, i.e. root surface area, present in the small P-enriched volume was the limiting factor in fertilizer P uptake. As a result, the apparent P recoveries per crop were low. They were about 10 % each growing season at a P rate of 22 kg/ha.Subseed placement at the start of each growing season is recommended, either placed alone or together with small amounts of cow dung. Then, plants benefit highly from both the startereffect of freshly-applied fertilizer and the residual effect of previously-applied (residual) fertilizer. P application rates of 20 to 40 kg/ha (in P 2 O 5 : 45 to 90 kg/ha) are advised for maize. At these rates, slightly more P is applied than plants require for producing maximum grain yields and the P availability of the soils will gradually increase by enlarging the soil volume enriched with fertilizer P. This repeated subseed placement fits in well with the low-input strategy and is probably easily adaptable in tropical small-scale farming systems.

De invloed van N-bemesting van voorgaande sneden op de ds-opbrengst en N-opname in een bepaalde snede wordt stikstofnawerking genoemd. Van 1971 t/m '74 zijn 6 proeven uitgevoerd, waarbij de nawerking van kunstmest-N van verschillende voorbehandelingen werd vergeleken

De invloed van N-bemesting van voorgaande sneden op de ds-opbrengst en N-opname in een bepaalde snede wordt stikstofnawerking genoemd. Van 1971 t/m '74 zijn 6 proeven uitgevoerd, waarbij de nawerking van kunstmest-N van verschillende voorbehandelingen werd vergeleken