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.     

Nitrogen and potassium fertilizer vs. nematode and weevil effects on yield and foliar nutrient status of banana in Uganda

Banana (Musa AAA) production is declining in central Uganda. A decline in soil fertility is often cited as one of the causes of the declining production. From 1996 to 1998, we studied banana yield responses to N and K fertilization at three sites in Uganda, where plantations ranged in age from 8 to 50 years. Phosphorus was applied to all treatments at 25 kg ha⁻¹, while N and K were applied (kg ha⁻¹) at 0N-0K, 0N-100K, 100N-0K, 100N-100K, and 100N-200K. Fresh fruit yields ranged from 4 to 67 Mg ha⁻¹ yr⁻¹. At one site the yield response to 100N-100K fertilization was significant (p < 0.01). The other sites showed positive but non-significant yield responses to N or NK fertilization. Economic analysis indicated that fertilizer use would be profitable only at the single site with significant yield increases. This site had negligible banana weevil (Cosmopolites sordidus (Germar)) and nematode (Radopholus similis; Helicotylenchus multicinctus) populations whereas the other sites were characterized by either severe nematode or weevil pressure. Fertilizer did not affect the damage caused by either nematodes or weevils. The best predictor of yield (p< 0.001, r ² = 0.75) was the number of functional leaves during anthesis. Measured soil nutrient parameters were highly variable but fell within sufficiency ranges. Foliar N contents were near diagnostic norms, but K levels fell below them, even when yields were satisfactory, suggesting that norms developed from other regions may not be suitable for Uganda. We conclude that in established plantations soil nutrient status is but one, and often a secondary, factor in the decline of banana yields in the central region of Uganda. Pest and disease infestations that result in reduced plantation productivity will need to be addressed before fertilizer use is likely to make a significant improvement in banana fruit yields. This revised version was published online in June 2006 with corrections to the Cover Date.     

Response of high yielding coconut variety and hybrids to fertilization under rainfed and irrigated conditions

A long-term experiment was conducted to study the differential fertilizer response of high yielding West Coast Tall variety, Chowghat Orange Dwarf (COD) × West Coast Tall (WCT) and WCT × COD hybrids of coconut for growth, nutrition, yield and economic returns under rainfed and irrigated conditions at Central Plantation Crops Research Institute, Kasaragod. The average yield for 8 years showed that the fertilizer treatment 1000 g N: 437g P: 1667g K palm^–1 yr^–1 (M₂) recorded significantly higher nut yield (136 nuts palm^–1 yr^–1) than M₁ treatment (500 g N: 218 g P: 833 g K palm^–1 yr^–1) and no fertilizer application (M₀). Amongst the variety/hybrids, the hybrid COD × WCT (128 nuts palm^–1 yr^–1) out yielded its reciprocal cross (114 nuts palm^–1 yr^–1) and WCT variety (115 nuts palm^–1 yr^–1). The growth parameters recorded did not show any significant difference in tree height and girth at base among the variety/hybrids. However, fertilizer application significantly increased the trunk height and girth at base. Annual application of fertilizers for a period of 32 years to coconut resulted in a marked increase in available phosphorus and potassium status in soil, but a marginal change in soil available nitrogen status was observed. Foliar contents of N remained below the critical levels of 1.8–2.0%. Phosphorus buildup in the soil due to fertilizers, did not reflect in the P contents of diagnostic leaf under both rainfed and irrigated conditions. Application of K fertilizer at M₁ level maintained K content of leaves at 1.07% i.e. just above the critical level (0.8–1.0%), whereas application of K fertilizers at M₂ level raised the leaf K content to 1.20%. The leaf nutrient contents did not vary much among variety/hybrids due to fertilizer application. The cost-benefit ratio was most favourable under fertilizer treatment M₁. For every rupee (Rs) invested on manuring, the total net return was Rs 2.80 under M₁ level and Rs 2.85 under M₂ level of fertilizers.     

Very high applications of nitrogen fertilizer on grassland and residual effects in the following season

At very high nitrogen applications (480 and more kg N ha^–1 yr^–1) in field trials on all-grass swards the amount of N applied exceeded the amount of N harvested. In the humid temperate climate of the Netherlands in the subsequent spring approximately 25, 40, and 50% of this excess nitrogen was recovered as accumulated mineral nitrogen in the 0–100 cm layer of sandy, clay and heavy clay soil, respectively. The effect of this excess nitrogen on growth during the subsequent season was measured through the increase in DM and N yield over a reference treatment. In this season all treatments received a uniform application (40 kg N ha^–1 cut^–1). Residual effects were absent on sandy soil but distinct on the clay soils. On the clay soils each accumulated kg soil mineral nitrogen produced 15 kg DM. Assuming a relatively small contribution of residual nitrogen carried over in stubble, roots and organic matter, the accumulated soil mineral nitrogen would seem to be as effective as applied fertilizer nitrogen.     

Organic matter management for soil conservation and productivity restoration in Africa: a contribution from Francophone research

Soil fertility is closely linked to soil organic matter (SOM), whose status depends on input, i.e., mainly biomass management, and output, i.e., mineralization, erosion and leaching. Preliminary results from runoff plots and lysimeters on hillslopes in West Africa indicated that carbon losses by erosion and leaching ranged between 10 and 100 kg C ha^?1 yr^?1, depending on annual rainfall and vegetal cover. Under natural conditions, losses may be low enough to be compensated by aerial deposits. But together with mineralization, erosion can locally be an important cause of SOM decrease in cropping systems where there is poor soil cover, steep slopes and erosive rain conditions. The effect of previous erosion on cereal production was assessed in case studies from Rwanda, Burundi, Cameroon, and Burkina Faso. On the densely populated hillslopes of Rwanda, hedges and manure reduced runoff and erosion efficiently, but did not succeed in improving grain yields due to P-deficiency of these ferrallitic soils. In Burundi, under similar conditions but under banana plantation, tree density and mulch cover had a strong influence on erosion; this previous erosion had an important effect on the next maize yield, even when the soils were amended with manure, mineral fertilizers and lime. On sandy ferruginous soils of North Cameroon, erosion increased with increasing tillage intensity. Manure application increased grain yield, but burying organic residues did not improve SOM levels and soil resistance to erosion. Mulching and tillage limited to the plant rows protected the topsoil against erosion, but did not clearly increase the yield. Manuring permitted the restoration of soil productivity, but additional mineral fertilizers (P, N) were needed to reach rapidly a high level of grain production. In the same way, experiments conducted with traditional Zaï system for restoring a degraded Entisol in Burkina Faso showed that runoff harvesting and organic matter input were not sufficient with no additional N and P fertilizers. Complementary experiments in Cameroon showed that a 4-mm selective sheet erosion and a 50-mm non-selective de-surfacing resulted in similar yield decline. Long fallowing, burning and grazing are traditional ways to utilize available biomass in Africa. Considering social habits and technical realities, it seems useful to balance ‘grazing-manuring’ and mulching in order to protect the soil and maintain its productive capacity. Minimum tillage with mulch (crop residues, weeds or legume fallow) is the new trend used for increasing crop production, with the help of herbicides. Agroforestry that produces good-quality litter is also a part of the solution.     

Calculated rates of soil acidification of intensively used grassland in the Netherlands

The major processes involved in acidification of soils under intensively managed grassland are the transformation and subsequent leaching of applied nitrogen (N), assimilation of excess cations in herbage and acidic atmospheric deposition. Carbonates from fertilizers and excess cations in purchased concentrates are the most important proton (H⁺) neutralizing agents applied to grassland. In this study, the effects of grazing, cutting and N application on the net proton loading from each of the main processes were calculated, using a simple model.On mown swards, simulated excess cation uptake by the sward released 4.5–9.3 kmol_c H⁺ ha^–1 yr^–1. The total proton loading on mown grassland decreased from about 8.0 to 5.3 kmol_c ha^–1 yr^–1 when fertilizer N input as CAN-27 increased from 0 to about 400 kg ha^–1 yr^–1. Contributions from atmospheric deposition ranged from 2.2 kmol_c ha^–1 yr^–1 when herbage yield exceeded 10 Mg ha^–1 yr^–1 to 3.0 kmol_c ha^–1 yr^–1 when herbage production was only 5.5 Mg ha^–1 yr^–1.On grazed swards, transformation of organically bound N from urine and dung to nitrate (NO ₃ ^- ) and the subsequent leaching of excess NO ₃ ^- was the main source of protons. Application of 400 kg N ha^–1 yr^–1 to grazed swards increased the proton loading from transformed N from 3.9 to 16.9 kmol_c ha^–1 yr^–1. The total proton loading on grazed swards exceeded that of mown swards when the input of fertilizer N exceeded 150 kg ha^–1 yr^–1.Underestimation of the amount of N immobilized in the soil biomass and lost by denitrification may have resulted in a slight overestimation of the amount of N lost by leaching and thereby also the simulated total proton loading.     

Twenty-five years of phosphate and potassium fertilization of a crop rotation

Effects of rate and placement of phosphate and potassium fertilizers was studied using a 4-year rotation of corn (Zea mays L.), soybeans (Glycine max L.), wheat (Triticum vulgare L.) and hay (later changed to corn). Yields increased with increased P until 22 kg P ha^–1 yr^–1 was applied. Yields increased with increased K applications to 140 kg K ha^–1 yr^–1. Broadcast P applications gave high yields than row applications. Crop response to P was affected more by soil P level than by application to the specific crop. Residual effect from K fertilizer applications did not last as long as the residual effect from P application. Soil tests for available P were closely correlated with rate of P application over the 25-year period. Soil tests for P were higher where P was banded where P was broadcast indicating less tie-up of P by the soil where less mixing occurred.Journal Paper No. 7910, Purdue University Agricultural Experiment Station.     

Pruning management effects on soil carbon and nitrogen in contour-hedgerow cropping with Leucaena leucocephala (Lam.) De Wit on sloping land in Haiti

Application of hedgerow prunings to the soil in alley cropping ispracticed to sustain crop yield but information is lacking on effects ofhedgerow management on soil C and N dynamics under continuous cropping.Cumulative effects of 3.5 years of leucaena [Leucaenaleucocephala (Lam.) De Wit] hedgerow management on soil organic CandN and potential C and N mineralization were determined in an alley croppingexperiment in Haiti. Treatments were combinations of pruning uses and pruningregimes in a 3 × 3 factorial with a no-tree control (rock walls) in arandomized complete block design with 3 replicates. A hedgerow + fertilizertreatment in an adjacent trial was included for comparison. Soil samplescollected at 0–5, 5–10 and 10–20 cm depths weresealed in mason jars and incubated at 25 °C for 30 days.Organic C and N and inorganic N were measured before the incubation. InorganicNand respired CO₂-C were measured after the incubation. After 3.5years, surface soil samples with prunings applied as mulch or incorporated atplanting had, respectively, 20 and 16% higher organic C, 34 and 18% higherorganic N concentrations, higher potential C and N mineralization and higherrelative N mineralization than with prunings removed. Soil C and N dynamicsweresimilar between pruning application methods. The two-cut regime with a longerregrowth period after cutting (0–40 DAP) had highest organic C in the0–20 cm soil layer whereas two-cut with a shorter regrowthperiod (0–30 DAP) had highest C turnover. Within soil layers, pruningapplication had higher organic C and N and potential C and N mineralizationthanthe no-tree control and alley plots with prunings removed in the 0–5cm layer whereas the latter treatments had similar C and Ndynamicsat all depths. Addition of N-P-K fertilizer in presence of fresh prunings didnot increase soil organic C and N but enhanced N dynamics in the surface soil.     

Impact of organic residue management on nitrogen use efficiency in an annual rice cropping sequence of lowland Central Thailand

Field experiments were conducted in Central Thailand under a rice–fallow–rice cropping sequence during consecutive dry and wet seasons of 1998 to determine the impact of residue management on fertilizer nitrogen (N) use. Treatments consisted of a combination of broadcast urea (70 kg N ha^–1) with rice straw (C/N 67) and rice hull ash (C/N 76), which were incorporated into the puddled soil 1 week before transplanting at a rate of 5 Mg ha^–1. Nitrogen-15 balance data showed that the dry season rice recovered 10 to 20% of fertilizer N at maturity. Of the applied N, 27 to 36% remained in the soil. Loss of N (unaccounted for) from the soil–plant system ranged from 47 to 54% of applied N. The availability of the residue fertilizer N to a subsequent rice crop was only less than 3% of the initial applied N. During both season fallows NO₃-N remained the dominant form of mineral-N (NO₃+NH₄) in the aerobic soil. In the dry season grain yield response to N application was significant (P=0.05). Organic material sources did not significantly change grain yield and N accumulation in rice. In terms of grain yields and N uptake at maturity, there was no significant residual effect of fertilizer N on the subsequent rice crop. The combined use of organic residues with urea did not improve N use efficiency, reduced N losses nor produced higher yields compared to urea alone. These results suggested that mechanisms such as N loss through gaseous N emissions may account for the low fertilizer N use efficiency from this rice cropping system. Splitting fertilizer N application should be considered on the fertilizer N use from the organic residue amendment.     

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.     

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.     

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.     

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.     

Carbon sequestration in soil aggregates under different crop rotations and nitrogen fertilization in an inceptisol in southeastern Norway

Effects of crop rotation and fertilization (nitrogen and manure) on concentrations of soil organic carbon (SOC) and total soil nitrogen (TSN) in bulk soil and in soil aggregates were investigated in a long-term field experiment established in 1953 at Ås, Norway. The effect of these management practices on SOC sequestration was estimated. The experiment had three six-course rotations: (I) continuous spring grain, (II) spring grain for 3 years followed by root crops for 3 years, and (III) spring grain for 2 years followed by meadow for 4 years. Three fertilizer treatments compared were: (A) 30–40 kg N ha^–1; (B) 80–120 kg N ha^–1; and (C) a combination of B and 60 Mg farmyard manure (FYM) ha^–1. All plots received a basal rate of PK fertilizer. Soil samples from these treatments were collected in autumn 2001 and analyzed for aggregate size, SOC and TSN concentrations. There were significant increases in 0.6–2 mm and < 0.6 mm aggregate size fractions, and reduction in the 6–20 mm and the > 20 mm sizes for rotation III only. There were also significant differences among rotations with regard to water stable aggregation. The order of increase in stability was II < I < III. Fertilizer treatment had no effect on aggregation or aggregate size distribution, but there was a slight tendency of increased stability with the application of FYM. Aggregate stability increased with increasing concentration of SOC (r2 = 0.53). The SOC and TSN concentrations in bulk soil were significantly higher in rotation III than in rotations II and I. Application of FYM increased SOC and TSN concentrations significantly in the 0–10 cm soil depth, but there were few significant differences between fertility treatments A and B. There was a trend of increase in concentration of SOC and TSN with decreasing aggregate size, but significant differences in these parameters in different aggregate size fractions were found only in few cases. The SOC and TSN concentrations were higher in >0.25 mm than in < 0.25 mm aggregates. The SOC sequestration rate was 77–167 kg SOC ha^–1 yr^–1 by increasing the N rate and 40–162 kg SOC ha^–1 yr^–1 by applying FYM. The SOC sequestration rate by judicious use of inorganic fertilizer was the greatest in the grain–meadow rotation, while that by application of FYM was the greatest in the all grain rotation.     

Fertilizer requirement of rice-wheat and maize-wheat rotations on coarse-textured soils amended with farmyard manure

Field experiments with rice-wheat rotation were conducted during five consecutive years on a coarse-textured low organic matter soil. By amending the soil with 12t FYM ha^–1, the yield of wetland rice in the absence of fertilizers was increased by 32 per cent. Application of 80 kg N ha^–1 as urea could increase the grain yield of rice equivalent to 120 kg N ha^–1 on the unamended soil. Although the soil under test was low in Olsen's P, rice did not respond to the application of phosphorus on both amended and unamended soils. For producing equivalent grain yield, fertilizer requirement of maize grown on soils amended with 6 and 12 t FYM ha^–1 could be reduced, respectively to 50 and 25 per cent of the dose recommended for unamended soil (120 kg N + 26.2 kg P + 25 kg K ha^–1). Grain yield of wheat grown after rice on soils amended with FYM was significantly higher than that obtained on unamended soil. In contrast, grain yield of wheat which followed maize did not differ significantly on amended or unamended soils.     

Studies on the substitution of inorganic fertilizers with organic manure and their effect on soil fertility in rice—wheat rotation

Field studies on the substitution of N and P fertilizers with farm yard manure (FYM) and their effect on the fertility status of a loamy sand soil in rice—wheat rotation are reported. The treatments consisted of application of 12 t FYM ha^–1 in combination with graded levels of N and P. Application of fertilizer N, FYM and their different combinations increased the rice yield significantly. There was no significant response to P application. The magnitude of response to the application of 12 t FYM and its combined use with each of 40 kg and 80 kg N ha^–1 was 0.7, 2.2 and 3.9 t ha^–1 respectively. Application of 120 kg N ha^–1 alone increased the yield by 3.9 t ha^–1, and was comparable to rice yield obtained with 80 kg N and 12 t FYM ha^–1. This indicated that 12 t FYM ha^–1 could be substituted for 40 kg N as inorganic fertilizer in rice. In addition FYM gave residual effects equivalent to 30 kg N and 13.1 kg P ha^–1 in the succeeding wheat. The effect of single or combined use of inorganic fertilizers and FYM was significantly reflected in the build up of available N, P, K and organic carbon contents of the soil. The relationship for predicting rice yield and nutrients uptake were also computed and are discussed.     

Initial and residual effects of nitrogen fertilizers on grain yield of a maize/bean intercrop grown on a Humic Nitosol and the fate and efficiency of the applied nitrogen

Initial and residual effects of nitrogen (N) fertilizers on grain yield of a maize/bean intercrop grown on a deep, well-drained Humic Nitosol (66% clay, 3% organic carbon) were evaluated. Enriched (¹⁵N) N fertilizer was used to study the fate of applied N in two seasons: using urea (banded) at 50 kg N ha^–1 in one season, and¹⁵N-enriched urea (banded), calcium ammonium nitrate (CAN, banded), and urea supergranules (USG, point placement) were applied in the other season (different field) at 100 kg N ha^–1. Nitrogen fertilizer significantly (P = 0.05) increased equivalent maize grain yield in each season of application with no significant differences between N sources, i.e., urea, CAN, and USG. Profitmaximizing rates ranged from 75 to 97 kg N ha^–1 and value: cost ratios ranged from 3.0 to 4.8. Urea gave the highest value: cost ratio in each season. Most (lowest measurement 81%) of the applied N was accounted for by analyzing the soil (to 150 cm depth) and plant material. Measurements for urea, CAN, and USG were not significantly different. The high N measurements suggest low losses of applied N fertilizer under the conditions of the study. Maize plant recovery ranged from 35 to 55%; most of this N (51–65%) was in the grain. Bean plant recovery ranged from 8 to 20%. About 34–43% of the applied N fertilizer remained in the soil, and most of it (about 70%) was within the top soil layer (0–30 cm). However, there were no significant equivalent maize grain increases in seasons following N application indicating no beneficial residual effect of the applied fertilizers.     

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.     

Modelling heavy metal and phosphorus balances for farming systems

Accounting for agricultural activities such as P fertilization in regional models of heavy metal accumulation provides suitable sustainable management strategies to reduce nutrient surpluses and metal inputs in agricultural soils. Using the balance model PROTERRA-S, we assessed the phosphorus (P), cadmium (Cd) and zinc (Zn) flux balances in agricultural soils of a rural region in Switzerland for different farm types and crop types. The P requirements of crops on arable farms were mainly supplied by commercial fertilizers and sewage sludge, while on animal husbandry farms P fertilizer demands were met by animal manure alone. Metal accumulation in soil was very different between the balance units. Estimated net Cd fluxes ranged between 1.0 and 2.3 g ha^–1 yr^–1 for arable farm types, 0.6 and 2.0 g ha^–1 yr^–1 for dairy and mixed farm types, and 9.1 and 17.8 g ha^–1 yr^–1 for animal husbandry farm types. Largest net Zn fluxes of 17.9–39.8 kg ha^–1 yr^–1 were estimated for animal husbandry farms, whereas for arable farm types net Zn fluxes of 101–260 g ha^–1 yr^–1 and for dairy and mixed farm types of 349–3360 g ha^–1 yr^–1 were found. The results indicate that P management is a primary factor determining the variation of these net Cd and net Zn fluxes. The latter were highly sensitive to the Zn/P concentration ratio in animal manure, atmospheric deposition and crop concentrations. Variation of net Cd fluxes resulted mainly from uncertainty in crop concentrations, atmospheric deposition, leaching parameters and uncertainty in Cd/P concentration ratio of commercial fertilizers. In addition, element balances were sensitive to empirical assumptions on fertilization strategy of farmers, such as the partitioning of manure between balance units.     

Effects of urea fertigation of apple trees on soil pH,exchangeable cations and extractable manganese in a sandy loam soil in New Zealand

Changes in soil pH, exchangeable aluminium (Al), calcium (Ca), magnesium (Mg), and potassium (K) and extractable manganese (Mn) were investigated after urea fertigation of a sandy loam soil in an apple orchard in New Zealand. Urea at three rates (0, 25, 50 kg N ha^–1 yr^–1 or 0, 16.9, 33.8 g N emitter^–1 yr^–1) was applied in 4 equal fertigations. Soil cores at 4 profile depths (0–10, 10–20, 20–40 and 40–60 cm) directly below and 20 cm from the emitter were sampled approximately 4 weeks after each fertigation and in the following winter. Results obtained showed that the largest changes in soil pH and cations occurred in soils directly below the emitter in the 50 kg N ha^–1 yr^–1 treatment where the soil pH decreased by 1.6 pH units at all soil depths. The lowest pH of 4.3 was observed at a depth of 27 cm. Exchangeable Al and extractable Mn levels increased to 11 meq kg^–1 and 78µg g^–1 respectively. Estimated losses of Ca, Mg and K from the upper soil profile depth (0–10 cm) represented 23, 63 and 27% of their respective total exchangeable levels. At lower profile depths (>20 cm), accumulation of displaced K was evident. Variable, and generally non-significant, chemical changes recorded in soils 20 cm from the emitter were attributed to restricted lateral water movement, and therefore urea movement, down the profile.The present study showed that one season of urea fertigation by trickle emitters, applied to a sandy loam, at half the rate conventionally applied to apple orchards (50 kg N ha^–1 yr^–1) resulted in pH and mineral element imbalances which were potentially and sufficiently severe to inhibit tree growth.