Historical role of manure application and its influence on soil nutrients and maize productivity in the semi-arid Ethiopian Rift Valley

Maize yield dynamics generally involve temporal changes, because increasing soil organic matter through manure application influences maize yields over the longer term, while inorganic nutrient application controls shorter term yields. These temporal soil properties and yield changes have been measured with long-term experiments. In sub-Saharan Africa (SSA), long-term experiments (more than 20 years) are rare due mainly to lack of funds. Farmers in the semi-arid northern Ethiopian Rift Valley (NERV) apply manure to maize fields in the long term. The relationships between the manure application levels, nutrient supply, soil nutrient levels, maize grain yields, and above-ground plant nutrient uptake levels were investigated by field measurement, interviews with farmers, laboratory analyses, and 2-years’ yield trials. The farmers applied on average 6.0 Mg ha^?1 yr^?1 of manure over 16.8 years on average. Significant linear or curve-linear correlations were found (1) between the annual nutrient supply and soil nutrient levels and (2) between the soil nutrient levels and maize productivities with minor exceptions. The regression equations determined from the yield trials proved 3.0 and 4.0 Mg ha^?1 of maize yields can be expected when soil available N contents were 3.9 and 5.1 mg kg^?1 in an ordinary rainfall year in NERV. For the farmers who apply 6.0 Mg ha^?1 yr^?1 manure, they are recommended to use 30 kg ha^?1 yr^?1 additional Urea to attain 3.0 Mg ha^?1 maize yields. These types of assessment methods do not require much cost, and yet it can provide long-term scientific information in SSA.     

Combining hill-placed manure and mineral fertilizer enhances maize productivity and profitability in northern Benin

Throughout much of Sub-Saharan Africa (SSA), maize production is characterized by low productivity due to the scarce availability and use of external inputs and recurrent droughts exacerbated by climate variability. Within the integrated soil fertility management (ISFM) framework, there is thus a need for optimizing the application of fertilizers and manure to better use the limited nutrient resources and increase crop yield and farmer income. An on-station experiment was conducted in Northern Benin over a 4-year period to evaluate the effect of hill placement of mineral fertilizer and manure on maize yields and soil chemical properties. The treatments consisted in the combination of three rates of manure (0 (NM), 3 (3M) and 6 (6M) Mg ha^?1) and three levels of fertilizer (0% (NF), 50% (50F) and 100% (100F) of the rate recommended by extension (76 kg N + 13.1 kg P + 24.9 K ha^?1)). On average across the fertilizer rates, hill-placement of manure significantly improved soil organic carbon content, available P and exchangeable K after 4 years by up to 124, 166 and 77%, respectively, compared to the initial values. As a result of the nutrient inputs and improved soil properties, yields increased steadily over time for all manure and fertilizer combinations. Value-cost ratios and benefit–cost ratios were >2 and generally as good or even better for treatments involving 50F compared to NF or 100F. Although applying half the recommended rate of fertilizer without manure as currently done by many farmers appears to make economic sense, this practice is unlikely to be sustainable in the long term. Substituting 50F for 3M or complementing 50F with 3M are two possible strategies that are compatible with the precepts of ISFM and provide returns on investment at least as good as the current practice. However, this will require greater manure production, made possible in part by the increased stover yields, and access to means of transportation to deliver the manure to the fields.     

Nitrogen availability to maize as affected by fertilizer application and soil type in the Tanzanian highlands

Enhancing crop production by maintaining a proper synchrony between soil nitrogen (N) and crop N demand remains a challenge, especially in under-studied tropical soils of Sub-Saharan Africa (SSA). For two consecutive cropping seasons (2013–2015), we monitored the fluctuation of soil inorganic N and its availability to maize in the Tanzanian highlands. Different urea-N rates (0–150 kg N ha^?1; split into two dressings) were applied to two soil types (TZi, sandy Alfisols; and TZm, clayey Andisols). In the early growing season, soil mineralized N was exposed to the leaching risk due to small crop N demand. In the second N application (major N supply accounting for two-thirds of the total N), applied urea was more efficient in increasing soil inorganic N availability at TZm than at TZi. Such effect of soil type could be the main contributor to the higher yield at TZm (up to 4.4 Mg ha^?1) than that at TZi (up to 2.6 Mg ha^?1) under the same N rate. The best-fitted linear-plateau model indicated that the soil inorganic N availability (0–0.3 m) at the tasseling stage largely accounted for the final yield. Further, yields at TZi were still limited by N availability at the tasseling stage due to fast depletion of applied-N, whereas yields plateaued at TZm once N availability was above 67 kg N ha^?1. Our results provided a valuable reference for designing the N management to increase yield, while minimizing the potentially adverse losses of N to the environment, in different agro-ecological zones in SSA.     

Maize-bean intercrop response to nutrient application relative to maize sole crop response

Maize-bean intercropping is important in sub-Saharan Africa. Maize sole crop (MSC) nutrient response has been much studied but data is scarce for determination of intercrop functions. A procedure for adapting MSC functions for the maize-bean intercrop was developed. Maize sole crop and intercrop responses were near parallel with notable exceptions for P in high potential areas for maize and for K. Mean intercrop bean yield with no nutrient application was about 0.4 Mg ha^?1 and increased on average by 24, 11 and ?3% with N, P and K application, respectively. Response function coefficients for MSC adjusted with the ratio of bean to maize grain value as the dependent variable accounted for nearly all variation in intercrop response coefficients providing the basis for determining intercrop response functions from MSC functions. Maize grain yield equivalent was less with MSC compared with intercrop; exceptions were for response to N in high potential areas and for bean to maize value ratios of two or less. The economically optimal rate of N and P were on average about 15% more but less for K with intercrop compared with MSC but with inconsistency. The economically optimal rate ranged widely with variation in the cost of nutrient use relative to grain value but generally without great effect on yield; an exception was a great effect on MSC yield response to N for high potential areas. Intercrop nutrient response functions can be reliably determined once maize sole crop functions are determined for a recommendation domain.     

Maximizing maize quality,productivity and profitability through a combined use of compost and nitrogen fertilizer in a semi-arid environment in Pakistan

In Pakistan, low crop yields are a common problem of sandy-loam arid and semi-arid agroecosystems. Poor nitrogen use efficiency (NUE) and widespread soil nitrogen (N) deficiency resulting from higher N losses are the main reasons for low yields. Compost may offer a nutrient source in this context as it is relatively stable, has a high NUE and crop N uptake, and may contribute to lower N losses in this region. This research conducted during 2011 and 2012, focused on application of N from poultry manure compost (PMC) and pressmud compost (PrMC) with urea in different ratios (0:0, 100:0, 75:25, 50:50, 25:75, 0:100) for sustainable maize production under the semi-arid conditions of Faisalabad. Overall, combined use of PMC and PrMC with urea in the 2 years increased the grain yield relative to the application of PMC and PrMC on their own. The greatest plant N uptake during the two years from PMC and urea at 25:75 was equivalent to mineral N management (0:100), and it resulted in maximum total grain yield (218.6%) and grain protein (19.8%). This resulted in the lowest N loss from the soil, and the largest NUE (19.1 kg kg^?1). Economically, this treatment also provided the greatest net income (932 US$ ha^?1), and a benefit cost ratio (2.1). Based on these results, PMC and urea at 25:75 was considered highly beneficial in increasing maize yield while reducing the loss of less-stable N from the soil, increasing NUE and N uptake in inherently poor soils. However, further evaluation is needed to decide whether this N nutrition strategy can be adopted on a wider scale.     

Effect of the integrated use of legume residue,poultry manure and inorganic fertilizers on maize yield,nutrient uptake and soil properties

Identification of a sustainable integrated soil fertility management option in the tropics will not only salvage the degraded soils but also enhances the attainment of the goal of food security. This study was conducted in 2004 and 2005 on a degraded tropical Alfisol in south western Nigeria to evaluate the effect of legume residue, poultry manure and inorganic fertilizers on maize yield, nutrient uptake and soil properties. The treatments consisted of two rates of poultry manure (0 and 5 t ha⁻¹), three rates of N fertilizer (0, 50 and 100 kg N ha⁻¹ applied as urea), three rates of P fertilizer (0, 30 and 60 kg P ha⁻¹ applied as single super phosphate) and two soybean treatments (with or without incorporation of legume residue) in various combinations as a factorial experiment in Randomized Complete Block design with three replicates. Results showed that poultry manure alone led to significant increase in maize yield (60%) and soil organic matter (45%). In contrast, legume residue incorporation gave significantly lower increase in yield (7%) and soil organic matter (11%). However, the combined application of poultry manure and legume incorporation led to 72% increase in maize yield as opposed to 63 and 10% increase recorded when manure alone or legume alone were incorporated, respectively. Optimal maize yield was achieved when manure application was integrated with P fertilizer application. The interaction of P fertilizer and legume incorporation indicated that soil phosphorus and maize P concentration were significantly increased with the application of the P fertilizer and legume incorporation. Hence, the application of P fertilizer alone is most likely to be economical compared with its integration with legume incorporation.     

Fate of labeled urea-15N as basal and topdressing applications in an irrigated wheat-maize rotation system in North China plain: II summer maize

A field micro-plot experiment for summer maize was conducted in an irrigated winter wheat (Triticum aestivum)-summer maize (Zea mays L.) rotation system in Mazhuang, Xinji of Hebei province in the North China Plain, using the ¹⁵N isotope method to determine the effects of N application (rates and timing) on urea-¹⁵N fate, residual N effects and N recovery efficiency (NRE) by maize. The experiment included three N rates (90, 180, and 270 kg ha^?1), divided by two ¹⁵N-labeled groups of basal-¹⁵N (30, 60, and 90 kg ha^?1, respectively) and topdress-¹⁵N (60, 120, and 180 kg N ha^?1, respectively). All of the treatments were irrigated two times, once at seeding time and once at topdressing time. The absorbed N in the maize plant derived from basal-N (6.8?C13%) and topdress-N (17?C30%) was identified. The residual N in the 0?C150-cm soil depth ranged from 45 to 60% at the first maize harvest, mainly retained in the top 20-cm layers. Both NRE in grain and total N recovery in plant in the first maize crop were higher from topdress-¹⁵N (26?C31 or 41?C51%, respectively) than from basal-¹⁵N (18?C23 or 34?C43%, respectively). The residual N in the 0?C150-cm soil layer was lower from topdress-¹⁵N (45?C47%) than from basal-¹⁵N (55?C60%) after the first maize harvest. Residual N recovery was 6?C11% in the second and 1.5?C3.5% in the third crop. Cumulative N recovery in the maize-wheat-maize rotations was higher from the topdress-¹⁵N (49?C59%) than from basal-¹⁵N and (45?C55%). The unaccounted N loss was 14?C24% from the basal-¹⁵N and 20?C33% from the topdress-¹⁵N, with a double dose of basal-¹⁵N application. An N rate of approximately 180 kg ha^?1 appears to be an effective application rate to optimum maize yield and NRE on North China Plain, depending on the residual N and the crop yield potential.     

Effects of nutrient cycling on grain yields and potassium balance

Soybean-maize rotation is a profitable cropping system and is used under rain fed conditions in north China. Since crop yields have been reported to decrease when K fertilizers are not used, we analyzed the productivity trends, soil-exchangeable and non-exchangeable K contents, and K balance in a continuous cropping experiment conducted in an area with an alfisol soil in the Liaohe River plain, China. The trial, established in early 1990 and continued till 2007, included 8 combinations of recycled manure and N, P, and K fertilizers. In the unfertilized plot, the yields of soybean and maize were 1,486 and 4,124 kg ha⁻¹ respectively (mean yield over 18 years). The yields of both soybean and maize increased to 2,195 and 7,476 kg ha⁻¹, respectively, in response to the application of inorganic N, P, and K fertilizers. The maximum yields of soybean (2,424 kg ha⁻¹) and maize (7,790 kg ha⁻¹) were obtained in the plots under treatment with N, P, and K fertilizers and recycled manure. K was one of the yield-limiting macronutrients: regular K application was required to make investments in the application of other mineral nutrients profitable. The decrease in the yields of soybean and maize owing to the absence of K application averaged 400 and 780 kg ha⁻¹, respectively. Soybean seed and maize grain yields significantly increased with the application of recycled manure. For both these crops, the variation coefficients of grain were lower with treatments that included recycled manure than without treatment. After 18 years, the soil-exchangeable and non-exchangeable K concentrations decreased; the concentrations in the case of treatments that did not include K fertilizers were not significantly different. Treatment with N, P, and K fertilizers appreciably improved the fertility level of the soil, increased the concentration of soil-exchangeable K, and decreased the non-exchangeable K concentration. In soils under treatment with N, P, and K fertilizers and recycled manure, the soil-exchangeable and non-exchangeable K levels in the 0–20 cm-deep soil layer increased by 34% and 2%, respectively, over the initial levels. Both soil-exchangeable and non-exchangeable K concentrations were the highest with on treatment with N, P, and K fertilizers and recycled manure, followed by treatment with N, P, and K fertilizers. These concentrations were lowest in unfertilized soils; the other treatments yielded intermediate results. The results showed a total removal of K by the crops, and the amount removed exceeded the amount of K added to the soil; in treatments that did not include K fertilizers, a net negative K balance was observed, from 184 to 575 kg ha⁻². The combined use of N, P, and K fertilizers and recycled manure increased the K content of the 0–20 cm-deep soil layer by 125% compared to the increase obtained with the application of N, P, and K fertilizers alone. The results clearly reveal that current mineral fertilizer applications are inadequate; instead, the annual application of recycled manure along with N, P, and K fertilizers could sustain future yields and soil productivity.     

Decomposition and phosphorus release of agroforestry shrub residues and the effect on maize yield in acidic soils of Rubona,southern Rwanda

Phosphorus release from decomposing leaf biomass of Calliandra calothyrsus Meissner, Tithonia diversifolia Hensley A.Gray and Tephrosia vogelii Hook.f. agroforestry species applied alone or combined with triple super phosphate (TSP) was studied at World Agroforestry Centre (ICRAF) laboratory for 56 days using an incubation method. The effects of above treatments on maize yield were evaluated in the field at Rubona, southern province of Rwanda between the years 2001 and 2004. The net cumulative phosphorus (P) mineralised ranged from 16.2 to 212.2 mg P kg⁻¹. The net P mineralisation rates from green manure, TSP applied alone or combined with green manure decreased in the order green manure > green manure + TSP > TSP > lime > control. The best plant residues quality for predicting P mineralisation is total P, C, and C:P & C:N ratios. Relative to the control, leaf biomass combined with TSP resulted in six times higher maize grain yield at the end of the experiment i.e., from 0.9 to 7.1 t ha⁻¹. In the fourth season, application of Tithonia diversifolia Hensley A.Gray green manure combined with TSP at 50 kg P ha⁻¹ resulted in higher maize yield (25% increase) than TSP and Tithonia diversifolia Hensley A.Gray (9% increase) applied alone at the similar rate. Therefore, application of plant residues and TSP alone might not be sufficient to meet maize plant P requirements and to achieve the yield potential of maize in the Rubona soils unless supplemented with mineral fertilisers.     

Residual phosphorus effects and nitrogen × phosphorus interactions in soybean–maize rotations on a P-deficient Ferralsol

Legume-cereal rotations are an essential component of integrated soil fertility management in low-input cropping systems, but strategies are needed to increase phosphorus (P) fertilizer use efficiency in such systems. These may include preferential targeting of P to one of the crops in the rotation cycle, the use of P-efficient genotypes, and the optimization of the rates of P fertilizer used. A field trial was conducted to evaluate the effects of increasing P fertilizer rates (0, 11, 22 and 44 kg P ha^?1, added as triple super phosphate) applied to three soybean genotypes grown on a P-deficient Ferralsol, on the nitrogen (N) and P nutrition of a subsequent maize crop. In addition, a greenhouse trial was set up to assess N, P and other rotation effects of three soybean genotypes on a subsequent maize crop relative to a maize–maize rotation at high and low P supply. In the field trial, soybean did not respond to increasing P rates, but residual P effects improved maize grain yields by up to 90 %. Ear leaf (field trial) and shoot (pot trial) P concentrations increased by applying N to maize, demonstrating important N × P interactions. The pot trial did not reveal a positive rotation effect of soybean on maize beyond the mere N-benefit, showing that soybean was not able to improve P availability to maize after correcting for the N-effect. No variation in rotation effects on maize among soybean genotypes was observed. Because of the absence of effects of the soybean crop on P availability to maize, opportunities to increase P fertilizer use efficiency in soybean–maize rotations mainly reside in maximizing P uptake by each crop separately and in matching P fertilizer rates with crop demand.     

Crop yields and soil organic carbon fractions as influenced by straw incorporation in a rice–wheat cropping system in southeastern China

In agro-ecosystems, the relationship between soil fertility and crop yield is mediated by manure application. In this study, an 8-year field experiment was performed with four fertilizer treatments (NPK, NPKM₁, NPKM₂, and NPKM₃), where NPK refers to chemical fertilizer and M₁, M₂, and M₃ refer to manure application rates of 15, 30, and 45 Mg ha^?1 year^?1, respectively. The results showed that the NPKM (NPKM₁, NPKM₂, and NPKM₃) treatments produced greater and more stable yields (4.95–5.45 Mg ha^?1 and 0.59–0.75) than the NPK treatment (4.01 Mg ha^?1 and 0.50). Crop yields under the NPKM treatments showed two trends, with a rate of decrease of 0.48–0.83 Mg ha^?1 year^?1 during the first 4 years and a rate of increase of 0.10–0.25 Mg ha^?1 year^?1 during the last 4 years. The soil organic carbon (SOC) significantly increased under all treatments. The estimated annual SOC decomposition rate was 0.35 Mg ha^?1 year^?1 and the equilibrium SOC level was 6.22 Mg ha^?1. Soil total nitrogen (N), available N, total phosphorus (P) and available P under the NPKM treatments increased by 0.15–0.26, 15–33, 0.17–0.66 and 45–159 g kg^?1, respectively, compared with the NPK treatment. Manure application mainly influenced crop yield by affecting the soil TN, available N, and available P, which accounted for up to 64% of the crop yield variation. Taken together, applying manure can determine or at least improve the effects of soil fertility on crop yield in acidic soils in South China.     

Crop response to manure and fertilizer in Burkina Faso and Niger

Farmyard manure (FYM) is valuable for soil management, especially for soils with <?10 g kg^?1 organic C in semi-arid West Africa. This study determined short-term FYM effects on yield and on response to N, P and K fertilizer for 20 trials in Niger and 28 trials in Burkina Faso involving six crops. The comparisons were of 0 and 2.5 Mg ha^?1 yr^?1 FYM applied in Niger, and of 0 and 5 Mg ha^?1 FYM applied once in 2 years in Burkina Faso. Fertilizer and FYM application alone had little effect on yield in Niger but there was a synergistic effect of fertilizer P with FYM which included increased mean responses to P of, respectively: 0.22 and 0.43 Mg ha^?1 for sorghum grain and fodder (Sorghum bicolor L.); 0.15 and 0.27 Mg ha^?1 for cowpea grain and fodder; 0.16 Mg ha^?1 grain for pearl millet (Pennisetum glaucum L.) when intercropped with cowpea (Vigna unguiculata L.); and 0.39 Mg ha^?1 for groundnut fodder (Arachis hypogea L.). Application of FYM increased pearl millet response to N but decreased legume response to K fertilizer. In Burkina Faso, there was a mean grain yield increase of 0.29 Mg ha^?1 yr^?1 due to FYM and the effect of applying both FYM and fertilizer was additive except for a synergy of N fertilizer plus manure application for maize (Zea mays L.). Therefore, farmers should apply FYM and fertilizer together in Niger but these can be applied alone or together in Burkina Faso with mostly similar effects.     

Nitrogen dynamics following slurry injection in maize: crop development

Using pig slurry as starter fertilizer for maize (Zea mays L.), injected below the row prior to planting is a reasonable way to omit application of additional mineral fertilizer in areas with intensive animal farming. However, delayed early growth and a lack of knowledge on nutrient availability limit the interest of farmers. To extenuate farmers concerns a field trial was conducted in 2014 and 2015 to get detailed information on nitrogen (N) uptake, the subsequent influences on crop growth at different vegetative growth stages and final yield of silage maize. Besides an unfertilized control, two liquid manure injection treatments (without and with nitrification inhibitor [NI]) were compared to slurry broadcast application + mineral N and phosphorus (P) starter fertilizer at planting (MSF). In 2014, NI treatment yields increased (+16.5%) and N uptake increased (+9.6%) compared to broadcast treatment. In 2015, cold and dry conditions during early growth limited P plant availability and reduced crop growth in treatments without MSF. However, when a NI was added to the slurry prior to application, plants showed less P deficiency symptoms and better growth. At harvest no differences between the fertilized treatments were observed. In both years apparent N recovery was increased when manure was injected (48% without, and 56% with NI, respectively) compared to broadcast application of manure (43%) indicating that N losses were lower. However, further knowledge on soil N transformation and N loss pathways in systems with slurry injection is needed.     

Yield response of maize (Zea mays L.) to crop residue management on two major soil types Of Alemaya, Eastern Ethiopia: I. Effects of varying rates of applied and residual N and P fertilizers

Field trials were conducted on two soil types for seven years (1988–1994) to investigate grain yield response of maize to crop residue application as influenced by varying rates of applied and residual N and P fertilizers. Yearly application of N and P fertilizers at both one-half and full recommended rates resulted in grain yield increases of more than 500 and 1100 kg ha-1, respectively over application of only crop residue. Moreover, grain yield responses due to residual N and P fertilizers applied only during the first year were found to be comparable to the yearly applications of these fertilizers. Rainfall and soil type have exerted considerable influences on the grain yield response obtained in this study. Grain yield exhibited a corresponding decrease with decreasing rainfall. Grain yield increases on Typic Pellustert were relatively higher than on Typic Ustorthent.     

Effect of manure application on crop yield and soil chemical properties in a long-term field trial of semi-arid Kenya

The sustainability of cereal/legume intercropping was assessed by monitoring trends in grain yield, soil organic C (SOC) and soil extractable P (Olsen method) measured over 13 years at a long-term field trial on a P-deficient soil in semi-arid Kenya. Goat manure was applied annually for 13 years at 0, 5 and 10 t ha⁻¹ and trends in grain yield were not identifiable because of season-to-season variations. SOC and Olsen P increased for the first seven years of manure application and then remained constant. The residual effect of manure applied for four years only lasted another seven to eight years when assessed by yield, SOC and Olsen P. Mineral fertilizers provided the same annual rates of N and P as in 5 t ha⁻¹ manure and initially ,gave the same yield as manure, declining after nine years to about 80%. Therefore, manure applications could be made intermittently and nutrient requirements topped-up with fertilizers. Grain yields for sorghum with continuous manure were described well by correlations with rainfall and manure input only, if data were excluded for seasons with over 500 mm rainfall. A comprehensive simulation model should correctly describe crop losses caused by excess water.     

Nutrient uptake of iron,zinc, magnesium,and copper in transgenic maize (<Emphasis Type="Italic">Zea mays</Emphasis>) as affected by rotation systems and N application rates

Understanding the interaction of macro- and micronutrients is a prerequisite to targeting nutrient balance in crop production. A 3-year field study was conducted to determine mineral nutrient uptake of maize hybrids with N fertilizer application under different rotation systems. The experiment was arranged in a split-plot design with rotation [maize-alfalfa (MA), maize-soybean (MS), and continuous maize (MM)] by N rate (0, 50, 100 and 150 kg N ha^?1) as the mainplot and hybrid as the subplot. Two additional treatments (200 and 250 kg N ha^?1) were tested in MM. Maize plant total Mg, Zn, and Cu content were in the order: MA?>?MS?>?MM. Plant Fe uptake was the lowest in MA and not affected by N input. The increased Cu uptake with increasing N rates indicated the synergism of these two nutrients, whereas dilution effects of N application on stover Zn and Mg concentrations were recorded. Rotation systems and N rates interactively affected nutrient harvest index and internal efficiency of Zn, Mg, Fe, and Cu. Relationships of plant N with Cu and Mg concentrations, and N with Zn, Mg, and Cu content at the V6 stage were established, but they were not necessarily preserved at maturity due to the progressive synergistic and dilution effects. The findings of nutrient uptake of Cu, Zn, Mg and Fe and their relationships with N nutrition in maize with stacked transgenic traits are important for developing best management practices to achieve concurrent improvements in nutrient use efficiency and crop productivity.     

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.     

Growth and yield response of glasshouse- and field-grown sweetpotato to nitrogen supply

Nitrogen (N) is an essential element for producing optimum crop yields, but negative responses to high N supply are commonly reported in sweetpotato (Ipomoea batatas) production. This study assessed contrasting responses of sweetpotato yield as a result of N application rates of 0, 30, 60, 90, 130, 160 and 230 kg ha^?1 in a glasshouse trial, and rates of 0, 50, 100, 150, 200 and 250 kg ha^?1, equivalent to 160, 210, 260, 310, 360 and 410 kg ha^?1 when soil N supply is included. The glasshouse-grown sweetpotato produced a maximum number and dry-biomass of storage roots, aboveground biomass and leaf area at 130 kg N ha^?1, while leaf N concentration peaked at 90 kg N ha^?1. Further increasing N application to 230 kg ha^?1 did not result in significant change in any of these attributes. In field-grown sweetpotato, leaf and storage root N concentrations increased with increasing N supply. Although N supply had no effect on the number of storage roots, total yield peaked at 260 kg ha^?1. Further increase of N supply reduced the total yield by up to 14% of the maximum yield. With increasing N supply, the glasshouse-grown sweetpotato yield linearly increased with leaf area; the arrangement of the trial permitting light interception to exceed the pot surface area. The yield reduction in field-grown plants was attributed to excess growth of aboveground parts, beyond that needed for efficient light capture. Respirational demand of the aboveground growth occurred at the expense of storage root yields.     

Nitrogen balances in farmers fields under alternative uses of a cover crop legume: a case study from Nicaragua

Canavalia brasiliensis (canavalia), a drought tolerant legume, was introduced into the smallholder traditional crop-livestock production system of the Nicaraguan hillsides as green manure to improve soil fertility or as forage during the dry season for improving milk production. Since nitrogen (N) is considered the most limiting nutrient for agricultural production in the target area, the objective of this study was to quantify the soil surface N budgets at plot level in farmers fields over two cropping years for the traditional maize/bean rotation and the alternative maize/canavalia rotation. Mineral fertilizer N, seed N and symbiotically fixed N were summed up as N input to the system. Symbiotic N₂ fixation was assessed using the ¹⁵N natural abundance method. Nitrogen output was quantified as N export via harvested products. Canavalia derived in average 69% of its N from the atmosphere. The amount of N fixed per hectare varied highly according to the biomass production, which ranged from 0 to 5,700 kg ha^?1. When used as green manure, canavalia increased the N balance of the maize/canavalia rotation but had no effect on the N uptake of the following maize crop. When used as forage, it bears the risk of a soil N depletion up to 41 kg N ha^?1 unless N would be recycled to the plot by animal manure. Without N mineral fertilizer application, the N budget remains negative even if canavalia was used as green manure. Therefore, the replenishment of soil N stocks by using canavalia may need a few years, during which the application of mineral N fertilizer needs to be maintained to sustain agricultural production.     

Manure and fertilizer contributions to soil mineral nitrogen and the yield of forage maize

Fifteen field trials were conducted to evaluate soil mineral N measurement as a means for quantifying the total N supply to forage maize and so to form the basis for fertilizer recommendations on a crop-specific basis. In every trial, 4 rates of cattle manure N (nominally 0, 80, 160, 240 kg N per ha) and 4 rates of ammonium nitrate (0, 50, 100, 150 kg N per ha) were factorially combined. Soil mineral N measurements were made before manure application, at the time of maize drilling, 7-10 weeks after drilling and after harvest. Measurements on control treatments which received no manure or ammonium nitrate showed extensive net mineralisation of soil N (mean 140 kg N per ha) in the 7-10 weeks after drilling followed by a decrease due to crop uptake, and probably net immobilisation, of approximately the same amount by harvest. This net mineralisation was probably the reason why only one trial showed a significant dry-matter yield response to ammonium nitrate. Results indicated that , to be useful for N recommendations, soil mineral N measurements should be taken 7-10 weeks after drilling. Only if the amount of mineral N at this time is less than expected crop N offtake should fertilizer N be applied. A mean of around 64% of the N applied in ammonium nitrate could be accounted for in soil mineral N after harvest of the maize, although this was reduced to 24% in the single trial where a dry-matter response to ammonium nitrate was recorded.