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.     

Nitrous oxide emissions from paddy soil in three rice-based cropping systems in China

Rice-flooding fallow, rice-wheat, and double rice-wheat systems were adopted in pot experiment in an annual rotation to investigate the effects of cropping system on N₂O emission from rice-based cropping systems. The annual N₂O emission from the rice-wheat and the double rice-wheat cropping systems were 4.3 kg N ha^–1 and 3.9 kg N ha^–1, respectively, higher than that from rice-flooding fallow cropping system, 1.4 kg N ha^–1. The average N₂O flux was 115 and 118 g N m^–2 h^–1 for rice season in rice-wheat system and early rice season in double rice-wheat system, respectively, 68.6 and 35.3 g N m^–2 h^–1 for the late rice season in double rice-wheat system and rice season in rice-flooding fallow, respectively, and only 3.1–5.3 g N m^–2 h^–1 for winter wheat or flooding fallow season. Temporal variations of N₂O emission during rice growing seasons differed and high N₂O emission occurred when soil conditions changed from upland crop to flooded rice.     

The uptake and distribution of mineral nutrients in the banana in response to supply of K,Mg and Mn

The effects of differential K, Mg and Mn supply on the uptake and distribution of N, P, K, Ca, Mg, Na, Mn, Cu and Zn in the Williams banana were examined over the three crop cycles. Plants were grown in sand culture in 1 m³ drainage lysimeters.In terms of total plant uptake the standard solutions used were balanced in respect of P, K and Ca, possibly low in Mg and high in Mn, Cu and Zn compared with field grown plants. K and Mg supply influenced total plant uptake of most elements similar to the way they influenced dry matter production. Exception were total plant uptake of Mg and Cu. High Mn supply depressed the uptake of Mg and Cu and increased the uptake of Mn sevenfold.Increase in K supply reduced the proportion of all nutrients, except K, retained in the roots and increased the proportion located in the fruit. A large proportion (20–36%) of N, P and K were located in the fruit, Ca, Mg and Mn accumulated in the trash (29–44%) and roots were high in Na, Cu and Zn (29–50%).     

Fertilizer responses of groundnuts (Arachis hypogae L.) under continuous intensive cultivation in the Nigerian savannah

Up until now, potash fertilization has not been part of the recommended practices for groundnut production in Nigeria and only low levels of P are recommended in line with the level of agricultural technology available to the farmer. The change from the traditional non-intensive farming practice to continuous intensive cultivation coupled with the introduction of better yielding/more-nutrient demanding crop varieties have led to a deficiency of a number of nutrients.Field experiments were carried out for 5 years (repeated on the same sites) at 8 locations in northern Nigeria to evaluate the effect of four levels of phosphorus (0, 8, 16 and 24 kg P ha^–1) and three levels of potassium (0, 20, and 40 kg K ha^–1) on yield and related parameters in groundnut. Soils at the various sites were essentially loamy sands with low levels of organic carbon and cation exchange capacity.The yield levels in the Guinea savannah were generally higher than those in the Sudan savannah but the response pattern was the same. There was significant response to applied P up to 24 kg P ha^–1. Potash applied at 20 kg K ha^–1 produced significantly higher pod yields than the control plots, but higher rates of applied K did not result in any further significant yield increase, although there was a clear consistent trend towards higher yields as the K rates increased. Phosphate X potash interaction had no significant effect on yield.Except for K, the uptake of all nutrients were significantly increased by P levels. However, only the K content of haulms and the N content of kernels were significantly increased by K application. On the average, about 58% of N, 68% of P, 19% of K, 5% of Ca and 22% of Mg were contained in the kernels while 27% of N, 23% of P, 64% of K, 83% of Ca and 69% of Mg were contained in the haulms. The implication of this is that the complete removal of groundnut residue will deplete the soil cation reverves rapidly unless these losses are compensated through fertilizer use.     

Nutrient balance of shifting cultivation by burning or mulching in the Eastern Amazon – evidence for subsoil nutrient accumulation

For over a hundred years shifting cultivation with slash-and-burn land preparation has been the predominant type of land use by smallholders in the Bragantina region of the Brazilian Eastern Amazon. This study contrasts the nutrient balance of slash-and-burn agriculture with a fire-free cultivation. Therefore, one half of a 3.5-year-old (28.7 t DM ha^–1) and a 7-year-old woody fallow vegetation (46.5 t DM ha^–1) was burnt and the other half mulched, leaving the biomass as a surface residue. Subsequently, a sequence of maize, beans and cassava was cropped for 1.5 year. Burning the 3.5- and 7-year-old fallow removed 97 and 94% of the C, 98 and 96% of the N, 90 and 63% of the P-stocks, and between 45 and 70% of the cations K, Mg and Ca of the aboveground biomass by volatilization or ash-particle transfer. These losses were avoided with the slash-and-mulch land preparation. Mulching did not increase the losses of nutrients by leaching, despite the high amount of rapidly decomposing surface mulch. Also the length of preceding fallow had no significant influence on leaching losses. At a depth of 3 m, leached nutrients were quantitatively negligible in both treatments. Comparing the nutrient fluxes at soil depths of 0.9 m, 1.8 m and 3 m, the amounts of all mobile nutrients, and also of chloride and sodium were markedly reduced during percolation and must have been retained. It is likely that nutrient retention in the subsoil layer is only temporary, emphasizing the need for a rapid re-establishment of the naturally deep-rooting secondary vegetation after abandonment of sites to enable uptake of these nutrients. The overall nutrient balance was highly negative for slash-and-burn. 291 and 403 kg N ha^–1, 21 and 18 kg P ha^–1, and 70 and 132 kg K ha^–1 were removed from the burnt plots with a preceding fallow of 3.5 and 7 years, respectively. A reduced fallow period (3.5 years), which is a common trend in the region, resulted in a higher mean annual rate of nutrient loss averaged over the duration of the cycle than a fallow period of 7 years. Eliminating the burning losses by mulching brought the agricultural system back to an equilibrated or even slightly positive nutrient balance, even after a reduced fallow period. Thus, slash-and-mulch is a viable alternative to maintain agricultural productivity and ecosystem functioning.     

Acidulated pegmatitic mica: A promising new multi-nutrient mineral fertilizer

Scrap grade pegmatitic phlogopite mica contains 5–7% K (8% K₂O), 10–14% Mg (23% MgO), 1–2% Ca (2.9% CaO), 0.03% Mn and 109 ppm Zn. On acidulation upto 65% of K and Mg and 15–100% Mn and Zn were recovered. Less than 13% of Ca was recovered in solution. Water soluble and Nh₄OAc extractable K and Mg of acidulated mica of pegmatitic origin increased a 10² to 10³ times compared to untreated mica. Acidulated mica remained non-hygroscopic even when mixed with acids at a 2:1 mica to acid ratio. X-ray diffraction analyses demonstrated that interlayer cations were easily leached from the mica structure leaving behind a kaolinitic residue, compared to the more stable tetrasilicate feldspars.The most significant achievement through these experiments was the yield increase obtained in the greenhouse experiment with rice by using the lowest application rate (200 kg ha^–1) so far reported for mica, - an exponential decrease from tonnes/ha previously reported. Acidulated phlogopite mica chips (200 kg ha^–1- 4 kg K, 8 kg Mg, trace elements Mn, Zn etc.) gave a yield increase of over 41% compared to a control with recommended muriate of potash and dolomite (17 kg K, 6 kg Mg). The response to acidulated feldspar (500 kg ha^–1- 1.5 kg K) and an acidulated feldspar-dolomite combined fertilizer (250 kg ha^–1- 0.6 kg K and 6 kg Mg) was not significant.The response to mica clearly shows a multinutrient deficiency in highly weathered tropical soils. The relatively high solubility of the acidulated mica, its range of nutrient element supply, its nonhygroscopic nature and its extremely simple manufacturing process makes mica, a cheap but effective fertilizer for the tropical regions where these nutrients are deficient, especially in highly metamorphosed crystalline terrains.     

Long-term effects of fallow systems and lengths on crop production and soil fertility maintenance in West Africa

In the development of short fallow systems as alternatives to shifting cultivation in West Africa, a long-term trial was established at the International Institute of Tropical Agriculture (IITA) on an Alfisol in the forest-savanna transitional zone of southwestern Nigeria, comparing three fallow systems; natural regrowth fallow, cover crop fallow and alley cropping on soil productivity and crop yield sustainability. The natural fallow system consisted of natural regrowth of mainly Chromolaena odorata shrub as fallow vegetation. The cover crop fallow system consisted of Pueraria phaseoloides, a herbaceous legume as fallow vegetation. The alley cropping system consisted of woody hedgerows of Leucaena leucocephala as fallow vegetation. The fallow lengths were 0 (continuous cropping), 1, 2 and 3 years after 1 year of maize/cassava intercropping. Biomass produced from natural fallow and cover crop fallow was burnt during the land preparation. Fertilizer was not applied throughout the study. Without fertilizer application, maize yield declined from above 3.0 t ha^–1 to below 0.5 t ha^–1 during 12 years of cultivation (1989–2000) on a land cleared from a 23-year old secondary forest. Temporal change in cassava tuber yield was erratic. Mean maize grain yields from 1993–2000 except for 1999 were higher in cover crop fallow system (1.89 t ha^–1) than in natural fallow system (1.73 t ha^–1), while natural fallow system outperformed alley cropping system (1.46 t ha^–1). During the above 7 years, mean cassava tuber yield in cover crop system (7.7 t ha^–1) did not differ from natural fallow system (8.2 t ha^–1), and both systems showed higher cassava tuber than the alley cropping system (5.7 t ha^–1). The positive effect of fallowing on crop yields was observed for both crops in the three systems, however, insignificant effects were seen when fallow length exceeded 1 year for cover crop and alley cropping, and 2 years for natural fallow. Soil pH, organic carbon, available P and exchangeable Ca, Mg and K decreased considerably after 12 years of cultivation, even in a 3-year fallow subplot. After 12 years, soil organic carbon (SOC) within 0–5 cm depth in alley cropping (13.9 g kg^–1) and natural fallow (13.7 g kg^–1) was higher than in cover crop fallow (11.6 g kg^–1). Whereas significant increase in SOC with either natural fallow or alley cropping was observed only after 2 or 3 years of fallow, the SOC in the 1-year fallow alley cropping subplot was higher than that in continuous cropping natural fallow subplot. It can be concluded from our study that in transforming shifting cultivation to a permanent cropping, fallow with natural vegetation (natural fallow), herbaceous legumes (cover crop fallow) and woody legumes (alley cropping) can contribute to the maintenance of crop production and soil fertility, however, length of fallow period does not need to exceed 2 years. When the fallow length is reduced to 1 year, a better alternative to natural regrowth fallow would be the cover crop for higher maize yield and alley cropping for higher soil organic matter. For fallow length of 2 years, West African farmers would be better off with the natural fallow system.     

Mineral nutrition and fertilizer response of grain sorghum in India — A review over the last 25 years

Researches on the mineral nutrition and fertilizer response of grain sorghum (Sorghum bicolor (L) Moench) carried out during the last 25 years in India are reviewed here. In general, N,P,K, Fe and Mn concentrations in vegetative plant parts decreased with crop age, while the concentrations of Ca, Mg and Cu increased. The concentration of N and P increased in panicle or grains of sorghum with advance in crop age. The seasonal change for other nutrients has not, however, been studied.Accumulation and uptake of N,P, and K by grain sorghum were characterized. Usually N and P accumulated slowly compared with the rapid accumulation of K in early crop growth stage and vice-versa in later stages of growth. As against the sizable mass of N and P into panicle, K was partitioned into stalk.Fertilizer responses to N and P were observed throughout India. Improved varieties and hybrids of sorghum responded to N rates ranging from 60 to 150 kg N ha^–1, whereas a response to P application was observed up to 40 kg P ha^–1. Although responses to K application had been inconsistent, an increase in grain yield of sorghum was observed due to 33 kg K ha^–1. A balanced fertilizer schedule consisting of 120 kg N ha^–1, 26 kg P ha^–1, 33 kg K ha^–1 and 15–25 kg Zn50₄ ha^–1 is recommended for improved productivity of grain sorghum.It is concluded that systematic research efforts should be directed so as to identify problem soils showing deficiencies and toxicities of different nutrients. Characterization of the seasonal changes in the concentration and uptake of different nutrients and determination of critical concentration and hidden hunger of different nutrients in plant tissues would lead to the recommendation of balanced fertilization for different sorghum-growing regions in India.A part of the paper presented in the Silver Jubliee Conference of Indian Society of Agronomy held at H.A.U., Hissar (India) in March, 1981     

Assessment of the ecological effects of forest fertilization using an experimental watershed approach

In the research project ARINUS, the effects of restabilization measures (fertilization with readily soluble MgSO₄) on the element cycling of Norway spruce ecosystems in the Black Forest (SW Germany) are studied. The objective is to quantify the natural and anthropogenic components of element cycling. Interrelations between the terrestrial and aquatic subsystem are assessed using an integrated approach which combines flux measurements in representative plots with input/output balances of small experimental watersheds. The paper discusses the initial effects of a whole-watershed treatment with Kieserite (750 kg ha^–1 MgSO₄ · H₂O) based on the Mg and S cycling in the control watershed. With the fertilizer, 130 kg ha^–1 Mg and 170 kg ha^–1 S were introduced into the system. Fertilization resulted in increased levels of Mg and S in the needles. Despite high inorganic Al concentrations and extremely low Ca/Al ratios in soil solution, there was no evidence for Al toxicity. Since fertilizer losses from the system 1 1/2 years (2 growing seasons) after the treatment have been modest, surface water was hardly been affected. More than 75% of the applied Mg has remained in the ecosystem, primarily in the intensively rooted upper soil layer. Also S has been retained to a considerable extent. The mobility of fertilizer sulfate in acidic forest soils is substantially lower than has been hitherto assumed from laboratory experiments. Therefore, fertilization with readily soluble sulfate-based Mg fertilizers is recommended as an efficient and — in comparison to liming — less risky restabilization measure on sites with a high potential for nitrification.     

Response of lowland rice and common bean grown in rotation to soil fertility levels on a Varzea soil

Brazil has approximately 30 million hectares of lowland areas, known locally as Varzea, but very little is known about their fertility and crop production potential. A field experiment was conducted for three consecutive years to evaluate response of lowland rice (Oryza sativa L.) grown in rotation with common bean (Phaseolus vulgaris L.) on a Varzea (low, Humic Gley) soil. Rice was grown at low (no fertilizer), medium (100 kg N ha^–1, 44 kg P ha^–1, 50 kg K ha^–1, 40 kg FTE-BR 12 ha^–1), and high (200 kg N ha^–1, 88 kg P ha^–1, 100 kg K ha^–1, 80 kg FTE-BR 12 ha^–1 fritted trace element-Brazil 12 as a source of micronutrients) soil fertility levels. Green manure with medium fertility was also included as an additional treatment. Average dry matter and grain yields of rice and common bean were significantly (P < 0.01) increased with increasing fertilization. Across the three years, rice yield was 4327 kg ha^–1 at low fertility, 5523 kg ha^–1 at medium fertility, 5465 kg ha^–1 at high fertility, and 6332 kg ha^–1 at medium fertility with green manure treatment. Similarly, average common bean yield was 294 kg ha^–1 at low soil fertility, 663 kg ha^–1 at medium soil fertility, 851 kg ha^–1 at high fertility, and 823 kg ha^–1 at medium fertility with green manure treatment. Significant differences in nutrient uptake in bean were observed for fertility, year, and their interactions; however, these factors were invariably nonsignificant in rice.     

The effects of a nitrification inhibitor on leaching losses and recovery of mineralized nitrogen by a wheat crop after ploughing-in temporary leguminous pastures

The effect of a nitrification inhibitor on the accumulation of ammonium (NH ₄ ⁺ -N) and nitrate (NO ₃ ^- -N) in the profile was investigated in two field experiments in Canterbury, New Zealand after the ploughing of a 4-year old ryegrass/white clover pasture in early (March) and late autumn (May). Nitrate leaching over the winter, and yield and N uptake of a following wheat crop were also assessed.The accumulation of N in the soil profile by the start of winter was greater in the March fallow (76–140 kg N ha^–1) than in the May fallow treatment (36–49 kg N ha^–1). The nitrification inhibitor dicyandiamide (DCD) did not affect the extent of net N mineralization, but it inhibited nitrification when applied to pasture before ploughing, especially at its depth of incorporation (100–200 mm). Nitrification inhibition in spring was greater when DCD was applied in May rather than in March due to its reduced degradation over the winter.Cumulative nitrate leaching losses were substantial from the March fallow treatment in both years (about 100 kg N ha^–1). A delay in the cultivation of pasture and the application of DCD both reduced nitrate leaching losses. When leaching occurred early in the winter (in 1991), losses were less when pasture was cultivated in May (2 kg N ha^–1) than when DCD was applied to pasture cultivated in March (68 kg N ha^–1). When leaching occurred late in the winter (in 1992), similar losses were measured from pasture cultivated in May (49 kg N ha^–1) and from DCD-treated pasture cultivated in March (57 kg N ha^–1).Grain harvest yield and N uptake of the following spring wheat crop were generally unaffected by the size of the N leaching loss over the winter. This was due to the high N fertility of the soil after four years of a grazed leguminous pasture.     

Identification of nutrients limiting cassava yield maintenance on a sedimentary soil in southern Benin,West Africa

Market opportunities will drive intensification of cassava production and fertilizer will play a role in this. A trial was initiated on 15 farmers fields (replications) in one village territory in Benin on a relatively fertile sedimentary soil site to identify nutrients limiting cassava yield using nutrient omission plots over three cropping years. There was no response to fertilizer in the first year when fresh root yields in the unamended control averaged 19.1 t ha^–1. In the second year, the control yield was 16 t ha^–1 and there were significant reductions from withholding P (3.5 t ha^–1) and K (2 t ha^–1) from a complete fertilizer regime. Nutrient balance after 1 and 2 years (cumulative) showed substantial P and K deficits in unamended plots. In the third year, the control yield was 12.9 t ha^–1 and effects of withholding K (5.3 t ha^–1), P (5.0 t ha^–1) and N (3.0 t ha^–1) were statistically significant. Soil K was a significant source of variation in yield in the third year. In the third year of annual nutrient additions soil P and K in the top 0.3 m were increased by 37 and 40%, respectively. Based on the cumulative nutrient balance calculation, the annual application needed to compensate nutrient depletion was 13 kg N, 10 kg P, and 60 kg K ha^–1. Partial budget analysis based on these amounts of fertilizer suggested that investment was clearly justified in the third year of continuous cropping at current low cassava prices.     

Measurement of nitrous oxide emissions from two rice-based cropping systems in China

A field experiment was conducted to investigate the effects of winter management and N fertilization on N₂O emission from a double rice-based cropping system. A rice field was either cropped with milk vetch (plot V) or left fallow (plot F) during the winter between rice crops. The milk vetch was incorporated in situ when the plot was prepared for rice transplanting. Then the plots V and F were divided into two sub-plots, which were then fertilized with 276 kg urea-N ha^–1 (referred to as plot VN and plot FN) or not fertilized (referred to as plot VU and plot FU). N₂O emission was measured periodically during the winter season and double rice growing seasons. The average N₂O flux was 11.0 and 18.1 g N m^–2 h^–1 for plot V and plot F, respectively, during winter season. During the early rice growing period, N₂O emission from plot VN averaged 167 g N m^–2 h^–1, which was eight- to fifteen-fold higher than that from the other three treatments (17.8, 21.0 and 10.8 g N m^–2 h^–1 for plots VU, FN, and FU, respectively). During the late rice growing period, the mean N₂O flux was 14.5, 11.1, 12.1 and 9.9 g N m^–2 h^–1 for plots VN, VU, FN and FU, respectively. The annual N₂O emission rates from green manure-double rice and fallow-double rice cropping systems were 3.6 kg N ha^–1 and 1.3 kg N ha^–1, respectively, with synthetic N fertilizer, and were 0.99 kg N ha^–1 and 1.12 kg N ha^–1, respectively, without synthetic N fertilizer. Generally, both green manure N and synthetic fertilizer N contribute to N₂O emission during double rice season.     

Response of two okra (Abelmoschus esculentus L. Moench) varieties to fertilizers: Growth and nutrient concentration as influenced by nitrogen and phosphorus application

The growth response and nutrient concentration in okra (Abelmoschus esculentus L. Moench) as influenced by four nitrogen rates (0, 25, 50 and 100 kg ha^–1) and three phosphorus rates (0, 13 and 26 kg ha^–1) were examined using two varieties (White velvet and NHAE 47-4). Nitrogen application generally increased fruit and shoot dry weights markedly whereas phosphorus increased them only moderately. Leaf and primary branch production and plant height were also enhanced by nitrogen fertilization up to 100 kg N ha^–1 but were not influenced by phosphorus application. The application of nitrogen enhanced the concentration of N, P and K in fruits and N and Mg in leaves while P and K concentrations in leaves were depressed. Nutrient concentrations in plant tissues were also partly a function of plant age and variety.     

Potassium and magnesium responses of cassava grown in Ultisol in southern Nigeria

Results of three consecutive croppings to study the potassium and magnesium responses of two improved cassava cultivars TMS 30395 and 30211 grown on an acid, sandy loam, Ultisol (Typic paleudult) in southern Nigeria is reported. On land newly cleared from Eupatorium fallow a significant potassium response in the first cropping year was observed only with the more vigorous cultivar TMS 30395. Both cultivars responded to potassium applications at rates of 30 and 60 kg Kha^–1 in second and third croppings respectively. A significant response to application of 20 kg Mgha^–1 was observed in the third crop with cultivar TMS 30211. Cultivar TMS 30395 seems to be more effective in utilizing magnesium from the soil. Potassium and magnesium responses on this Ultisol can be expected when the IN Ammonium Acetate extractable soil K and Mg test levels are 0.15 me K 100g^–1 and 0.20 meMg 100g^–1, respectively. Critical tissue concentrations of cassava index leaves sampled at 6 MAP are 0.1% K for both cultivars and 0.33% Mg for cultivar TMS 30211.     

Comparison of the fertilizing effects of ash from burnt secondary vegetation and of mineral fertilizers on upland rice in south-west C?te d'Ivoire

An important reason for burning the slashed vegetation in shifting cultivation systems is the release of nutrients. In an experiment in the Taï region, S.W. Côte d'Ivoire the fertilizing effects of ash and mineral fertilizers were compared. The ash was derived from a 20-year-old secondary forest which was slashed, dried, piled together and burned. The nutritional value of ash was compared with that of N, P, K fertilizers and lime in a field trial consisting of a fertilizer portion and an ash portion. The experimental design of the fertilizer portion was a 3⁴ factorial. The application rates per ha were 0, 50, 100 kg N (urea); 0, 12.5, 25 kg P (triple superphosphate); 0, 50, 100 kg K (KCl); 0, 400, 800 kg Ca(OH)₂. The 81 treatment combinations were divided into nine subblocks. To each of these subblocks three experimental units were added. In six of them ash was applied at rates of 0, 4000 and 8000 kg ash ha^–1. With 4000 kg ash ha^–1 31 kg P, 264 kg K, 915 kg Ca, 150 kg Mg, 10 kg Na, 10 kg Mn, 2.6 kg Zn and 32 kg S were applied. Upland rice (cultivar IDSA 6) was grown as test crop. The grain yields on individual experimental units varied from 1.2 to 3.2 t ha^–1. In the 3⁴ trial, N and P application significantly affected the yields of grain and straw. P application increased the uptakes of N, P, K, Ca and Mg significantly. N uptake was also significantly increased by N application and liming. There was a significant negative quadratic P effect on grain and straw yield, and uptake of nutrients, indicating that higher application rates did not result in higher yields and uptake of nutrients.Ash application significantly increased the yields of grain and straw and the uptakes of N, P, K and Mg, but not of Ca. It was concluded from the two trials that the response to ash application was mainly a P effect.The recovery fractions of P at about the same P applications rates were 7.4% and 11%, in the ash and 3⁴ trial, respectively. Hence, the relative effectiveness of ash-P was 0.67 or 67%, and the substitution rate 1.5. This implies that for the uptake of a unit of P about 1.5 times as much ash-P as fertilizer-P should be applied.The effectiveness of ash as liming material was 0.59 compared to Ca(OH)₂, hence 1.7 times as much ash as Ca(OH)₂ is needed to establish a same increase in pH. The CaO equivalent of ash proved to be 44% and the CaCO₃ equivalent 78%. In the ash trial a higher efficiency of utilization of absorbed P was found than in the 3⁴ trial. Several possible causes of this difference are discussed but no conclusive answers could be given.     

Potassium and magnesium fertilizers on banana in Uganda: yields, weevil damage, foliar nutrient status and DRIS analysis

Low soil fertility and pest pressure are two causes of the decline in banana (Musa AAA) production in central Uganda. Foliar analysis by the Diagnosis and Recommendation Integrated System (DRIS) pinpoints K and Mg as the most limiting nutrients. This study tested the effects of K and Mg additions on plant performance and weevil damage for 2.75 yr, at Buligwe in central Uganda and Muyogo in southwest Uganda. All treatments received 25 kg P ha^–1 and 100 kg N ha^–1 annually, while K and Mg were applied (kg ha^–1) at 0 K–0 Mg, 100 K–0 Mg, 100 K–25 Mg and 100 K–50 Mg. Fresh fruit yields (Mg ha^–1 yr^–1) ranged from 3.2 to 5.0 at Buligwe and 14.4 to 18.9 at Muyogo, with similar treatment trends at both sites. The 100 K–0 Mg treatment produced higher yields than no-K control (p = 0.022 for the combined dataset). Yields with K+Mg tended to be lower than with K only, though not significantly different. Foliar nutrient concentrations were little affected by treatments, but varied substantially among sample dates. With increasing cumulative rainfall between foliar samplings, foliar P declined (p = 0.077), K declined (ns), and Ca and Mg increased (p = 0.02 to 0.03). Weevil damage was higher at Buligwe, but was little affected by K and Mg treatments at either site.     

Response to fertilization and nutrient deficiency diagnostics in peach palm in Central Amazonia

Peach palm (Bactris gasipaes Kunth) is increasingly grown in the tropics for its heart-of-palm and fruit. Determining fertilization response and diagnosing nutrient status in peach palm may require methods that consider the particularities in nutrient acquisition and recycling of perennial crops. Responses to nutrient additions, and the diagnostic value of soil and foliar analyses were examined in three field experiments with three-year old peach palm stands on Oxisols in Central Amazonia. To diagnose P-deficiency levels in soils, samples from 0–5 cm and 5–20 cm depth were analyzed for available P by different methods (Mehlich-1, Mehlich-3 and Modified Olsen). The second and fifth leaves were analyzed to assess N, P and K deficiencies. Field experiments involved several combinations of N (from 0 to 225 kg ha^–1 yr^–1), K (from 0 to 225 kg ha^–1 yr^–1) and P (from 0 to 59 kg ha^–1 yr^–1). Palms on control plots (unfertilized) and those receiving 225 kg ha^–1 yr^–1 N and 2 Mg ha^–1 of lime yielded between 4 and 19% of the maximum growth which was obtained with N, P and K applications. In one of the experiments, yield of heart-of-palm was positively related to N additions at the lowest levels of P (8.6 kg ha^–1 yr^–1) and K (60 kg ha^–1 yr^–1) additions. In one experiment, critical leaf N level was 2.5% for the second leaf and 2.2% for the fifth leaf. Some growth responses to P additions at constant N and K levels were observed (e.g., 797 kg ha^–1 yr^–1 of heart-of-palm with 39.3 kg ha^–1 yr^–1 of applied P, and 632 kg ha^–1 yr^–1 of heart-of-palm with 10.9 kg ha^–1 yr^–1 of applied P in one experiment, and 2334 kg ha^–1 yr^–1 of heart-of-palm with 39.3 kg ha^–1 yr^–1 of P and 1257 kg ha^–1 yr^–1 of heart-of-palm with 19.7 kg ha^–1 yr^–1 of P in another trial). In the experiment for fruit production from peach palm, total plant height did not respond to P additions between 19.7 and 59 kg ha^–1 yr^–1 and K additions between 75 and 225 kg ha^–1 yr^–1. Leaf P levels were found to be above the proposed critical levels of 0.23% for the third leaf and 0.16% for the fifth leaf. Plants in this experiment, however, showed evident symptoms of Mg deficiency, which was associated with a steep gradient of increasing Mg concentration from the fifth leaf to the second leaf. Standard leaf diagnostic methods in most cases proved less useful to show plant N and P status and growth responses to N and P additions. Soil P determined by common extractions was in general too variable for prediction of growth.     

The comparison of nitrogen use and leaching in sole cropped versus intercropped pea and barley

The effect of sole and intercropping of field pea (Pisumsativum L.) and spring barley (Hordeum vulgareL.) and of crop residue management on crop yield,NO₃ ^– leaching and N balance in the cropping systemwas tested in a 2-year lysimeter experiment on a temperate sandy loam soil. Thecrop rotation was pea and barley sole and intercrops followed by winter-rye anda fallow period. The Land Equivalent Ratio (LER), which is defined as therelative land area under sole crops that is required to produce the yieldsachieved in intercropping, was used to compare intercropping performancerelative to sole cropping. Crops received no fertilizer in the experimentalperiod. Natural ¹⁵N abundance techniques were used to determine peaN₂ fixation. The pea–barley intercrop yielded 4.0 Mg grainha^–1, which was about 0.5 Mg lowerthan theyields of sole cropped pea but about 1.5 Mg greater than harvestedin sole cropped barley. Calculation of the LER showed thatplant growth resources were used from 17 to 31% more efficiently by theintercrop than by the sole crops. Pea increased the N derived fromN₂fixation from 70% when sole cropped to 99% of the total aboveground Naccumulation when intercropped. However, based upon aboveground N accumulationthe pea–barley intercrop yielded about 85 kg Nha^–1, which was about 65 kg lower thansolecropped pea but about three times greater than harvested in sole croppedbarley.Despite different preceding crops and removal or incorporation of straw, therewas no significant difference between the subsequent non-fertilized winter-ryegrain yields averaging 2.8 Mg ha^–1, indicating anequalization of the quality of incorporated residue by theNO₃ ^– leaching pattern.NO₃ ^– leaching throughout the experimental periodwas61 to 76 kg N ha^–1. Leaching dynamics indicateddifferences in the temporal N mineralization comparing lysimeters previouslycropped with pea or with barley. The major part of this N was leached duringautumn and winter. Leaching tended to be smaller in the lysimeters originallycropped with the pea–barley intercrops, although not significantly differentfromthe sole cropped pea and barley lysimeters. Soil N balances indicated depletionof N in the soil–plant system during the experimental period, independent ofcropping system and residue management. N complementarity in the croppingsystemand the synchrony between residual N availability and crop N uptake isdiscussed.     

Mineral nutrition of slash pine in subtropical Australia. II. foliar nutrient response to fertilization

In the previous paper, we reported the stand growth of slash pine (Pinus elliottii) during the first 11.5 years of plantation in response to (1) initial fertilization at plantation establishment with P rates of 11, 22, 45 and 90 kg P ha^–1 which were either banded or broadcast in the presence or absence of basal fertilizers containing 50 kg N ha^–1, 50 kg K ha^–1 and 5 kg Cu ha^–1 and (2) application of additional 40 kg P ha^–1 at age 10 years. Here we present the responses in foliar nutrient concentrations of slash pine in the first 11.5 years to the initial fertilization and the additional P applied at age 10 years.Foliar N and K concentrations in the first 9.6 years of plantation decreased with the initial P rate. Application of the basal fertilizers improved foliar Cu concentration. Foliar Ca and Mg concentrations increased linearly with the initial P rate. The initial fertilization did not affect foliar Mn concentration in the first 9.6 years. Foliar P concentration increased quadratically with the initial P rate, which accounted for 77–86% of the variation in foliar P concentration. Most of the explained variation in foliar nutrient concentrations was attributable to the plantation age except for foliar P concentration. In the case of foliar P concentration, 53% was explained by the initial P rate, 31% by the plantation age and 2% by the positive interaction between the initial P rate and the plantation age. Foliar P concentration of slash pine at age 11.5 years increased quadratically with the initial P rate and linearly with the additional 40 kg P ha^–1 applied at age 10 years, accounting for 81% of the variation in the foliar P concentration. Foliar nutrient analysis indicated that P was the major limiting nutrient affecting the stand growth of slash pine in the first 11.5 years.