Investigation on the use of macro- and micro-nutrients to improve maize yield in South Western Nigeria

Investigation into the use of macro- and micro-nutrients to increase maize yield was conducted in both the glasshouse and in the field. The glasshouse studies involved ten soil series commonly cultivated to maize in South Western Nigeria, while the field studies were conducted on one soil at Ibadan.Dry matter yield increased above the control with a single application of N, P, K, Ca, Mg, Fe, Cu, Zn and Mn, suggesting that most of the soils in the South Western Nigeria require additions of each of these elements for increased maize production. The size of the response to each element varied from series to series. Soils which were high in organic matter (over 3%) required the lowest N dressings for optimum dry matter yield of maize.In the field studies, a fertilizer combination which included N, P, K, Mg and the micro nutrients Fe, Cu and Zn gave a higher relative yield than the single application of N, P, K, and a combination of NP, NK, Pk or NPK.In the South West Zone of Nigeria, there is no soil testing programme and fertilizers applied by farmers and researchers have not increased yields as expected. Average maize yield on farmers' field is less than 1000 kgha^–1 while on research stations it is 2500 kgha^–1. When compared with 7000 kgha^–1 in U.S.A., these yields are still very low.Different recommendations for the major plant nutrients have been made by many workers in the South West zone based on fertilizer trials [1, 5, 8, 13, 16].None of the recommendations have included the micronutrients and secondary nutrients and the objective of this project was to supply relevant information on this important aspect.     

Effect of different nitrogen levels,plant population and soil nutrient status on yield and yield components of maize (Zea mays L.) in different ecological zones of Nigeria

Field studies on the effect of nitrogen levels, plant population and soil nutrient status on maize yield and yield components at eight different sites representing six different ecological maize growing zones of Nigeria conducted during 1976, 1977 and 1978 indicated that N significantly influenced yield at six of the eight sites, NIFOR, Umudike and Uyo (rain forest zone), Mokwa and Samaru (Savanna zone) and Riyom (derived savanna zone). Optimum N required for maize varies between 50 and 100 kgN in the different zones. There was no response to spacing except at Umudike, Uyo and Riyom, and no significant interaction between N and spacing at any location. Nitrogen application significantly influenced earweight at Ikenne, NIFOR, Umudike, Uyo and Mokwa. Nitrogen application had a significant effect on the number of cobs at NIFOR, Uyo and Mokwa, while spacing significantly influenced number of cobs at all locations except Uyo. Husk weight was significantly increased by nitrogen application at four locations, NIFOR, Uyo, Mokwa and Samaru, but spacing had no effect on this yield component in any of the other locations except Umudike. There was an N by spacing interaction on husk weight at Umudike and Mokwa. Nitrogen application significantly influenced lodging at tasseling at Uyo, Mokwa and Riyom, whilst there was a significant effect of spacing at Uyo and Samaru. At harvest, lodging was not influenced by N application but spacing significantly affected lodging at Ibadan and NIFOR. Both N application and spacing had no significant effect on shelling percentage at any location. The high correlation between relative yield and available Zn(r = 0.77), Cu (r = 0.63) and Fe (r = ? 0.66) of the soil at all the locations has shown that:

1. other nutrients besides N, P and K affected maize yield, therefore the inclusion of other nutrients besides N, P and K in the fertilizer recommendation for maize should be encouraged;
2. different levels of NPK fertilizer plus other nutrients are required in each ecological zone and this can be determined by soil testing.

     

Relationship between soil physical and chemical characteristics and ear-leaf concentration of P,K, Mg,Zn, Fe,Cu, Mn and relative yield of maize in soils derived from sedimentary rocks of South-Western Nigeria

In a four-season field experiment conducted in 18 locations covering two different ecological zones of the sedimentary forest soils of South-Western Nigeria, relationships were established by simple correlation between the ear-leaf content of P, K, Mg, Zn, Fe, Cu, Mn, relative yield of maize (RY), soil physical characteristics and soil nutrient status. Soil pH was strongly related to the relative yield, soil clay, available P, exchangeable Ca, K, Zn, and Mn in soils, P and Cu concentration in the ear-leaf.Organic matter did not appear to play a very significant role in nutrient supply or relate to nutrient element concentration in the ear-leaf and relative yield in soils that are relatively low in soil organic matter.Nitrogen was not determined. Phosphorus among all the elements determined seemed to have a high significant effect on Ca, K, Zn, Mn and RY. However, the effect on RY was negative. Manganese in both soil and ear-leaf had the highest negative significant relationship with yield in the zone.The multiple regression analysis indicated a relationship meaning that the soil physical and chemical properties and ear-leaf content of the elements P, K, Mg, Zn, Fe, Cu, Mn are important to maize cultivation in this zone. Hence consideration of a combination of soils and plant factors are essential before meaningful fertilizer recommendation can be made for maize in the zone under study.     

Recycling of nutrients in Japanese mint - assessment of soil fertility and crop yield

The efficiency of mint-residue, composted alone and amended with starter nutrients, microbial culture and soil suspension (hereafter termed amended compost) was compared with farm yard manure and inorganic fertilizer on the yield of Japanese mint (Mentha arvensis L.) and improvement of soil fertility. Herbage, essential oil yield, nutrient uptake of Japanese mint and soil available nutrients were significantly enhanced due to application of amended compost as compared to nonamended compost, farm yard manure and inorganic fertilizer. Organic fertilized soils maintained significantly higher available nutrients throughout the crop growth period as compared to inorganic fertilized soils. No additional improvement in yields and soil fertility was recorded with combined application of compost and inorganic fertilizer in 1:1 ratio as against addition of compost alone. Advantage of such combinations was recorded in case of farm yard manure. Results of the study suggested possibilities for nutrient recycling through composted mint-residue for supplementing the fertilizers requirement of Japanese mint.     

Novel water-soluble polymer coatings control NPK release rate,improve soil quality and maize productivity

We investigated different combinations of polymers (5% each) (i) starch, gelatin (polymer coating; PC-1), (ii) polyvinyl alcohol (PVA), gum Arabica (PC-2), (iii) PVA, gelatin (PC-3), (iv) starch, gum Arabica (PC-4), (v) gelatin, gum Arabica (PC-5), (vi) starch, PVA (PC-6), for coating NPK (17, 17:17) in a fluidized bed granulator. Morphological characterization indicated a uniform coating of all formulations on NPK granules. A slow release of N (PC-3), P (PC-6), and K (PC-3) was observed in water. In soil, high mineral N (63%), plant-available P (72%), and K (24%) were observed in PC-3, PC-5, and PC-6, respectively than uncoated fertilizer. Microbial biomass NPK was also higher in these treatment. This resulted in higher maize yield (66%), N (114%), P (164%), and K (137%) uptakes and apparent N (267%), P (196%), and K (358%) recoveries from applied fertilizer in these treatments. Among these, PC-3 resulted in an increase of 115% shoot N, 169% P and 138% K uptakes and 268% apparent N, 206% P and 361% K recoveries than uncoated fertilizer. Hence, coating of NPK with this biodegradable polymer combination controlled N, P, and K release and synchronized these nutrients availabilities with maize nutrients demand therefore resulted in higher maize crop yield and nutrient utilization efficiencies.     

Nitrogen use efficiency by maize as affected by a mucuna short fallow and P application in the coastal savanna of West Africa

Maize is the primary food crop grown by farmers in the coastal savanna region of Togo and Benin on degraded (rhodic ferralsols), low in soil K-supplying capacity, and non-degraded (plinthic acrisols) soils. Agronomic trials were conducted during 1999–2002 in southern Togo on both soil types to investigate the impact of N and P fertilization and the introduction of a mucuna short fallow (MSF) on yield, indigenous N supply of the soil, N recovery fraction and internal efficiency of maize. In all plots, an annual basal dose of 100 kg K ha^–1 was applied to the maize crop. Maize and mucuna crop residues were incorporated into the soil during land preparation. Treatment yields were primarily below 80% of CERES-MAIZE simulated weather-defined maize yield potentials, indicating that nutrients were more limiting than weather conditions. On degraded soil (DS), maize yields increased from 0.4 t ha^–1 to 2.8 t ha^–1 from 1999 to 2001, without N or P application, in the absence of MSF, with annual K application and incorporation of maize crop residues. Application of N and P mineral fertilizer resulted in yield gains of 1–1.5 t ha^–1. With MSF, additional yield gains of between 0.5 and 1.0 t ha^–1 were obtained at low N application rates. N supply of the soil increased from 10 to 42 kg ha^–1 from 1999 to 2001 and to 58 kg N ha^–1 with MSF. Application of P resulted in significant improvements in N recovery fraction, and greatest gains were obtained with MSF and P application. MSF did not significantly affect internal N efficiency, which averaged 45 kg grain (kg N uptake)^–1. On non-degraded soils (NDS) and without N or P application, in the absence of MSF, maize yields were about 3 t ha^–1 from 1999 to 2001, with N supply of the soil ranging from 55 to 110 kg N ha^–1. Application of 40 kg P ha^–1 alone resulted in significant maize yield gains of between 1.0 (1999) and 1.5 (2001) t ha^–1. Inclusion of MSF did not significantly improve maize yields and even reduced N recovery fraction as determined in the third cropping year (2001). Results illustrate the importance of site-specific integrated soil fertility management recommendations for the southern regions of Togo and Benin that consider indigenous soil nutrient-supplying capacity and yield potential. On DS, the main nutrients limiting maize growth were N and probably K. On NDS, nutrients limiting growth were mainly N and P. Even on DS rapid gains in productivity can be obtained, with MSF serving as a means to allow farmers with limited financial means to restore the fertility of such soils. MSF cannot be recommended on relatively fertile NDS.     

Using mucuna and P fertilizer to increase maize grain yield and N fertilizer use efficiency in the coastal savanna of Togo

To reduce severe soil degradation associated with agriculture an intensified land-use system is being promoted in West African countries. Most soils of the West African savanna zones are so poor that the efficiency of mineral fertilizers, if applied, is very low. For this reason and because of their high cost and unavailability, many small-scale farmers are reluctant to apply fertilizer. This work investigates a fertilizer management strategy using integrated soil fertility management with a leguminous cover crop (mucuna) so as to improve the soil fertility and increase the use efficiency of fertilizer. The experiment was conducted in the coastal savanna of Togo at Djaka Kopé. The aim was to evaluate the effectiveness of mucuna short fallow (MSF) in increasing maize grain yield through an improved use efficiency of mineral fertilizer. A 2-year maize–mucuna relay intercropping system was compared with continuous sole maize cropping. Fertilizer treatments were factorial combinations of 0, 50 and 100 kg nitrogen (N) ha^–1 and 0, 20 and 40 kg phosphorus (P) ha^–1. While maize grain yield was significantly increased by N fertilization, P did not show any important effect on grain yield. With no N and P applied, grain yield after MSF was on average 40% (572 kg ha^–1) higher than without. The response to N was much greater than the response to MSF, indicating that N was undoubtedly the key element for maize yield building. P fertilization and MSF together positively influenced the apparent N recovery fraction (NRF). N uptake alone did not reflect on its own the yield obtained, and the relationship between grain yield and N uptake is shifted by MSF, with the grain yield increase per unit of N uptake being higher with than without MSF. Combining MSF and P fertilization may therefore lead to improved N use efficiency, making the application of fertilizer N (lower rates) more attractive to small-scale farmers.     

Managing soil fertility diversity to enhance resource use efficiencies in smallholder farming systems: a case from Murewa District,Zimbabwe

Smallholder farms in sub-Saharan African exhibit substantial heterogeneity in soil fertility, and nutrient resource allocation strategies that address this variability are required to increase nutrient use efficiencies. We applied the Field-scale resource Interactions, use Efficiencies and Long-term soil fertility Development (FIELD) model to explore consequences of various manure and fertilizer application strategies on crop productivity and soil organic carbon (SOC) dynamics on farms varying in resource endowment in a case study village in Murewa District, Zimbabwe. FIELD simulated a rapid decline in SOC and maize yields when native woodlands were cleared for maize cultivation without fertilizer inputs coupled with removal of crop residues. Applications of 10 t manure ha⁻¹ year⁻¹ for 10 years were required to restore maize productivity to the yields attainable under native woodland. Long-term application of manure at 5 and 3 t ha⁻¹ resulted in SOC contents comparable to zones of high and medium soil fertility observed on farms of wealthy cattle owners. Targeting manure application to restore SOC to 50–60% of contents under native woodlands was sufficient to increase productivity to 90% of attainable yields. Short-term increases in crop productivity achieved by reallocating manure to less fertile fields were short-lived on sandy soils. Preventing degradation of the soils under intensive cultivation is difficult, particularly in low input farming systems, and attention should be paid to judicious use of the limited nutrient resources to maintain a degree of soil fertility that supports good crop response to fertilizer application.     

Organic residue management,soil nutrient changes and maize yield in a humid Ultisol

A study was conducted on an Oxic Paleudult in South Western Nigeria to evaluate the effects of organic residue treatments after clearing a 3 year secondary fallow land on soil nutrients, maize yield and profitability. Burning of the fallow residue in 1993 and crop residue in situ in 1994 led to significant increases in soil pH, total N, organic matter, available P, exchangeable Ca, Mg and K within one month in both fertilized and unfertilized treatments. However, the increases were not sustained till harvest and in most cases the concentrations of the nutrients decreased significantly below the pretreatment levels. Increases due to residue incorporation were small but more sustainable, while in bare unfertilized plots the nutrients decreased below the pre treatment levels throughout the period of the experiment. Maize yields were significantly higher in residue incorporated and burnt plots than in the bare plots with or without fertilizer application in both years. The influence of fertilizer application was profound. However, residue incorporation without fertilizer produced 84% of the yield obtained in bare fertilized plots in 1993 and as much as 104% in 1994. The highest profit was obtained when fertilizer application was combined with residue incorporation.     

Are Partial Nutrient Balances Suitable to Evaluate Nutrient Sustainability of Land use Systems? Results from a Case Study in Central Sulawesi,Indonesia

Nutrient input–output balances are often used as indicators for the sustainability of land use systems. In a case study on plot scale in Central Sulawesi, Indonesia, we measured nutrient input–output balances of natural rainforest and two unfertilized land use systems (maize, and coffee/cacao agroforestry). These are the two major land use systems on converted rainforest sites in this part of Sulawesi. We wanted to test if (a) plant nutrient balances are negative, (b) which pathway is most important for losses of plant nutrients, and (c) if partial plant nutrient balances are suitable to evaluate sustainability of the land use systems. We measured nutrient inputs by precipitation and nutrient outputs by harvest export and leaching. We selected two locations, the first was situated on a fertile Cambisol developed on alluvial sediment soil, and the second on a less fertile Cambisol developed on weathered phyllite substrate. Nutrient losses through leaching were higher on sites with higher soil fertility. Nutrient balances in natural forest on fertile soils were negative for N, Ca, K and Mg. Inputs of P by precipitation and outputs by leaching were below detection limit. On less fertile soils, leaching of N and K in natural forest was lower than inputs by precipitation. As net nutrient losses were highest in agroforestry, followed by maize and natural forest stands, forest conversion into agricultural land will result in increased nutrient losses. Main output pathway of N, P and K was harvest, whereas main output pathway for Ca and Mg was through leaching. The annual losses of nutrients we measured were higher than in comparable studies on nutrient poor soils; however losses were only small fractions of available nutrient stocks. Our results showed negative partial nutrient balances in both agricultural systems. Nutrient balances in this study were more influenced by native soil fertility than by land use. Because we found indirect evidence that some nutrient pathways, which were not measured, may have significantly changed the overall balance (biological N fixation, weathering), we conclude that partial nutrient balances are no good indicators for sustainability of land use systems.     

Fertility status of soils of the derived savanna and northern guinea savanna and response to major plant nutrients, as influenced by soil type and land use management

Although the fertility status of soils in the West African moist savanna is generally believed to be low, crop yields on farmers' fields vary widely from virtually nil to values near the potential production. The soil fertility status was evaluated for a number of farmers' fields selected at random in 2 villages (Zouzouvou and Eglimé) representative for the derived savanna (DS) benchmark area and in 2 villages (Danayamaka and Kayawa) representative for the Northern Guinea savanna (NGS) benchmark area. The relation between soil fertility status and soil type characteristics and fertilizer use was explored. In an accompanying missing nutrient greenhouse trial, the most limiting nutrients for maize growth were determined. While soils in the DS villages were formed on different geological units, soils in the NGS villages could be differentiated according to their position on the landscape. Generally, soils in the DS contained a smaller amount of silt (104 vs. 288 g kg^–1), a larger amount of sand (785 vs. 584 g kg^–1), C (9.3 vs. 6.3 g kg^–1), N (0.7 vs. 0.5 g kg^–1), Olsen-P (10.7 vs. 5.4 mg kg^–1), and had a higher CEC (7.0 vs. 4.8 cmolc kg^–1) than soils in the NGS villages. The large silt content of the soils in the NGS is a reflection of the aeolian origin of the parent material. Within the benchmark areas, general soil fertility characteristics were similar in the villages in the NGS, except for a larger amount of particulate organic matter in Kayawa than in Danayamaka. This may also have led to a significantly larger amount of ammonium-N content in the 0–20 and 20–40 cm soil layers in Kayawa compared to Danayamaka (42 vs 24 kg N ha^–1 in the 0–20 cm soil layer). Differences in topsoil soil characteristics between the DS villages were a reflection of differences in clay quality (kaolinitic vs. 2:1 clay minerals) of the parent material and past fertilizer use. The Olsen-P and exchangeable K contents were observed to increase with increased fertilizer application rate in both benchmarks, while fertilizer application rate had no significant effect on the organic C or total N content of the soil nor on its ECEC. The response of maize shoot biomass production to applied N was similar for both benchmarks (biomass accumulation in the treatment without N was, on average, 55% of the biomass production in the treatment which received all nutrients), while soils in the NGS responded more strongly to applied P than soils in the DS (37% vs 66% of biomass production in the treatment which received all nutrients). The more favourable P status of soils in Eglimé (DS) was attributed to the more intense use of P fertilizers, as a result of government-supported cotton production schemes. Response to cations, S or micronutrients were neglegible. A significant linear relationship was found between the soil Olsen-P content and the response to applied P up to levels of 12 mg kg^–1 in the topsoil. Above this level, a plateau was reached.     

关于化肥对作物产量贡献的评估问题

化肥对作物产量的贡献率包括化肥对当季作物产量的贡献、化肥后效的贡献和由化肥增殖的有机肥的贡献,即Ct%=CNPK当%+CNPK后%+CNPK有%。以玉米为例,按某一肥料配比计算化肥对玉米产量的总贡献率为58.6%,与国内外从中长期试验中获得的化肥实际贡献率在50%左右相似,明显高于化肥对当季作物的增产率(34.6%),远高于单一养分(氮)对作物产量的贡献率(18.2%)。     

Improved water control and crop management effects on lowland rice productivity in West Africa

Much of the rapidly-growing demand for rice in West Africa will be met from production in inland valley swamps which are abundant and relatively robust with regard to cropping intensification. Rice yields in the traditional, predominating non-bunded systems are low (about 1.5 Mg ha^?1). Informal development of traditional rainfed lowlands is currently occurring across the region, mainly with low-cost interventions such as the building of field bunds. Relating lowland rice yield to quantitative information on resource base quality and agronomic practices will improve future research priorities and guide site and system-specific targeting of available technical options. Diagnostic on-farm trials were conducted in 62 traditional and 40 improved (bunded) rainfed lowland fields in three agro-ecological zones of Côte d'Ivoire (Guinea savanna, bimodal forest, and monomodal forest zones) to quantify effects of improved water control on productivity. Weed biomass and rice grain yield were determined in farmers' fields and in super-imposed researcher-managed subplots (clean weeding, zero N control treatment, and mineral fertilizer N application). Grain yield variability was attributed to agronomic practices using multiple regression analysis. Bunding significantly increased rice grain yield across sites by about 40% and controlled weeds, with approximately 25% less weed biomass in bunded than in open plots. Mineral fertilizer N application significantly increased rice yields (18% on average across sites) only in bunded fields, where N use efficiency was 12 compared to 4 kg of rice grain per kg of applied N in open fields. Across environments, about 60% of the observed variability in rice grain yields was explained by water control and the timing of agronomic management interventions (weeding, N application). The increased development of lowland rice areas through the construction of field bunds has the potential to significantly increase rice production in West Africa, while also possibly reducing labor requirements for hand weeding and allowing for a more efficient use of mineral N fertilizers. The benefits from construction of bunds are likely to be largest in the relatively well-drained inland valleys of the savanna and bimodal rainfall forest, compared to the high-rainfall monomodal forest zones.     

Fertiliser strategies for improved nutrient use efficiency on sandy soils in high rainfall regimes

Fertiliser application strategies for maize (Zea mays L.) production on sandy soils under high rainfall regimes need to be carefully designed to minimise nutrient losses through leaching and maximise crop yield. Experiments were conducted to determine N, P, and K leaching in sandy soils with 3–6% clay in surface layers under maize production, and the effectiveness of different N, P, and K fertiliser timing and splitting strategies on leaching of N, P, and K and on maize yield. In a column experiment on an Oxic Paleustult (Korat series) with 3% clay, leaching of N, P, and K from fertiliser (114N-17P-22K in kg ha⁻¹) was significant under simulated rainfall, but decreased to negligible levels with 3–5 split applications of fertiliser. Maize N and K uptake increased with 3–5 split applications, but not P uptake. Despite continued intense rainfall and further fertilizer additions, leaching was not recorded after day 30, and this was attributed to the effect of plant water uptake on reducing deep drainage. Split applications of fertilizer maintained NP and K in the 0–30 cm layer during 30–60 days when maize nutrient demand was likely to be at its highest, while in the recommended fertilizer regime NPK in the surface layers declined after 30 days. In a field experiment on an Oxic Paleustult (Korat series) with 6% clay, 3–4 splits of fertiliser increased N and K uptake and increased maize yields from 3.3 to 4.5 Mg ha⁻¹. Postponing basal fertiliser application from pre-planting to 7–15 days after emergence increased uptake of N, P, and K and grain yield emphasising the greater risk of nutrient losses from fertiliser applied at planting than later. Strategies designed to reduce the amount of nutrients applied as fertiliser at planting, such as split application and postponing basal application can decrease the risk of leaching of N, P, and K from fertiliser and improve nutrient use efficiency, and grain yield of maize on sandy soils under high growing season rainfall regimes.     

Powdered granite is not an effective fertilizer for clover and wheat in sandy soils from Western Australia

Granite (silicate) rock dust, a by-product of quarry operations, is being advocated and used as a fertilizer in the wheatbelt of south-western Australia (WA). The dust is insoluble and based on its nutrient element content (1.9% K and 0.3%P and negligible N) it is not expected to be a useful fertilizer. Previous laboratory studies and glasshouse experiments in WA suggest the dust is a slow release K fertilizer. This paper extends the previous studies to consider the dust as an NP or K fertilizer in the year of application in a field experiment on a soil deficient in N, P and K. In addition, the effectiveness of the dust as a K fertilizer was compared with the effectiveness of KCl (muriate of potash), the K fertilizer used in WA at present, in glasshouse experiments using K deficient soils. In the field experiment, compared with NP fertilizer or NPK fertilizer (urea, supplying N; superphosphate, providing P, S, Ca, Cu, Zn and Mo; KCl providing K), the dust had no effect on grain yield of wheat (Triticum aestivum); in fact dust applied at 20 t ha^-1, for unknown reasons, reduced yields by about 65% compared to the nil (no fertilizer, no dust) treatment. Relative to the nil treatment, applying NPK fertilizer increased yields about threefold, from 0.54 to 1.79 t ha. The glasshouse experiments showed that, relative to KCl, the dust was from about 0.02 to 14% as effective in K deficient grey sandy soils for producing dried tops of 30-day old wheat plants or 42-day old clover (Trifolium subterraneum) plants. In soils with adequate K (yellow sands, sandy loams or clays, loamy clays, clay loams and clays), neither KCl nor the dust affected yields of 30 to 42-day old wheat or clover plants grown in the glasshouse. In the glasshouse experiments, no yield depressions were measured for the dust applied up to 17 g dust per kg soil (equivalent to 17 t dust ha^-1 mixed into the top 10 cm of soil in the field). It is concluded that the dust has no value as a fertilizer.     

Effect of tree foliage of locust bean (Parkia biglobosa) and neem (Azadirachta indica) on soil fertility and productivity of maize in a savanna alfisol

Organic matter (OM) management is key to sustainable fertility and productivity of tropical soil systems. Short-term evaluation of the potentialsof foliage of neem and locust bean in soil fertility improvement, as measured by the productivity of maize, was carried out on a savanna Alfisol from 1995 to1997. The trees are indigenous to the savanna, and common in farms and homesteads in the region. The objective was to determine the effects of theseeasily renewable and cheap OM sources on maize response to applied inorganic fertilizer and soil chemical properties. Treatments consisted of three sourcesof organic matter: no-OM, neem and locust bean, and three rates of inorganic fertilizer, applied at 0, and of the recommended rate of120–27–50 NPK for maize, which in addition served as check. Results obtained over the three seasons were consistent, and revealed that neem wassuperior to locust bean by a factor of 2 and also to no-OM treatments, but were all inferior to the recommended fertilizer rate (with a maximum yield of 3.75t/ha). Isolated relative effects for neem and locust bean only in the third year were 138% and 86% respectively, and declined progressively withincreasing levels of applied inorganic fertilizer. This trend was consistent for the three years, during which soil productivity (relativity index) clearlyappreciated. Results also revealed that P and organic C accumulation was greater with locust bean, but neem decomposed faster and depressed pH less, a clearindication that indices of soil productivity may not always be tied to OM or absolute values of soil properties alone in savanna soil systems. The studyalso revealed that the effects of the tree foliages, the inorganic fertilizer rates and the interactions were significant at various levels of probability forgrain, stover, plant height, available P, OM and pH. There was the possibility of better crop performance with combinations of OM and inorganic fertilizer levels for the soils. Integrated fertility management systems using 3 tons of neem foliage and recommended inorganic fertilizer rate produced a goodmaize crop, and offers an economically viable option for the resource poor maize farmers of the Nigerian savanna.     

Soil and leaf nutrient interactions following application of calcium silicate slag to sugarcane

In certain areas of the Everglades Agricultural Area, plant and ratoon sugarcane (Saccharum L.) yields are increased by application of Si from calcium silicate slag. The greatest yield responses are obtained in the plant crop the first year after application of slag and when plant uptake of Si is increased. Magnesium deficiencies have been reported after slag application. The objective of this study was to quantify interactions of soil and leaf nutrients on sugarcane grown on a Terra Ceia muck (Euic, hyperthermic Typic Medisaprist) that had previously received calcium silicate slag. Slag was applied at five rates, and yields were evaluated from plant, first-ratoon, and second-ratoon (stubble) crops at two locations. Soil and leaf from each crop were sampled for nutrient analysis and the results were used to interpret the yield data. Although slag increased cane yield by as much as 39% and sugar yield by 50%, for each 100 mg L^–1 drop in extractable soil Mg, cane yields declined by 5.3 Mg ha^–1 and sugar yields by 0.9 Mg ha^–1. At leaf Si concentrations exceeding 10 g kg^–1, optimum cane and sugar yields were observed, while leaf Mg concentrations approached critical leaf concentrations below 1.5 g kg^–1. Estimates of total leaf nutrient uptake during each crop indicated that uptake of Mg did not meet nutrient demands at high biomass production. Nutrient antagonism between Si and Mg is suggested. Low soil Mg may contribute to the marked crop responses to slag and for the decline in stubble production. Application of a magnesium fertilizer may be necessary to maintain high nutrient availability.Contribution from the University of Florida, Institute of Food and Agricultural Sciences. Florida Agric. Exp. Stn., Journal Series no. R-00859.     

Nitrogen fertilizer equivalencies of organics of differing quality and optimum combination with inorganic nitrogen source in Central Kenya

Decline in crop yields is a major problem facing smallholder farmers in Kenya and the entire Sub-Saharan region. This is attributed mainly to the mining of major nutrients due to continuous cropping without addition of adequate external nutrients. In most cases inorganic fertilizers are expensive, hence unaffordable to most smallholder farmers. Although organic nutrient sources are available, information about their potential use is scanty. A field experiment was set up in the sub-humid highlands of Kenya to establish the chemical fertilizer equivalency values of different organic materials based on their quality. The experiment consisted of maize plots to which freshly collected leaves of Tithonia diversifolia (tithonia), Senna spectabilis (senna) and Calliandra calothyrsus (calliandra) (all with %N>3) obtained from hedgerows grown ex situ (biomass transfer) and urea (inorganic nitrogen source) were applied. Results obtained for the cumulative above ground biomass yield for three seasons indicated that a combination of both organic and inorganic nutrient source gave higher maize biomass yield than when each was applied separately. Above ground biomass yield production in maize (t ha^–1) from organic and inorganic fertilization was in the order of senna+urea (31.2), tithonia+urea (29.4), calliandra+urea (29.3), tithonia (28.6), senna (27.9), urea (27.4), calliandra (25.9), and control (22.5) for three cumulative seasons. On average, the three organic materials (calliandra, senna and tithonia) gave fertilizer equivalency values for the nitrogen contained in them of 50, 87 and 118%, respectively. It is therefore recommended that tithonia biomass be used in place of mineral fertilizer as a source of nitrogen. The high equivalency values can be attributed to the synergetic effects of nutrient supply, and improved moisture and soil physical conditions of the mulch. However, for sustainable agricultural production, combination with mineral fertilizer would be the best option.     

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.     

Effect of NPK fertilization on the mineral nutrition and yield of three coconut genotypes

Annual application of NPK fertilizers over a 18 year period to coconut on red sandy loam soils resulted in a minimal increase in mineralisable N, but in a marked increase in available P and K. Plant N levels, however, reflected the improved N nutrition but did not reach sufficiency levels found elsewhere. An available P status of 15 ppm in the control plots kept leaf P at sufficiency levels. P fertilizers did not increase the P content of leaves. K fertilizers raised the K leaf content to sufficiency levels. Doubling the M₁ fertilizer rates of 500 g N, 220 g P and 830 g K per palm per year had no effect on N, P and K levels in the palm leaves.Changes in K levels of the leaves had antagonistic effects on leaf Mg (r = – 0.68^**) and leaf Na (r = – 0.87^**). As this effect brings leaf Mg close to deficiency values palms receiving K might need additional Mg as well.The findings and interpretation of soil and leaf analysis data were confirmed by large yield responses to application of NPK fertilizers. Genetic differences between palms in their response to levels of nutrient supplies were apparent. The CDO × WCT hybrid outyielded the high yielding WCT variety especially when NPK was given at the M₁ level. The response in yield to applied fertilizers was linear for WCT and curvilinear for the hybrids CDO × WCT and WCT × CDO.