Effect of organic and inorganic phosphorus sources on maize yields in an acid soil in western Kenya

Maize production in western Kenya is commonly limited by P deficiencies and aluminum phytotoxicity. Due to high costs of imported fertilizers and lime, focus is now shifting to solutions that utilize local resources. We tested the effect of three inorganic P sources i.e., triple superphosphate (TSP), Minjingu phosphate rock (MPR) and Busumbu phosphate rock (BPR), each applied in combination with two organic materials (OMs) i.e., farmyard manure (FYM) and Tithonia diversifolia green manure (tithonia), or with urea on soil chemical properties related to soil acidity, P availability and maize yields for three consecutive seasons in western Kenya. The OMs and inorganic P sources were applied to provide 20 and 40 kg P ha⁻¹ respectively in their combination. Where urea was used, the inorganic P sources were applied at 60 kg P ha⁻¹. Maize did not respond to application of TSP, MPR or BPR with urea in the first two seasons. However, after three seasons, maize significantly responded to application of MPR with urea. FYM was more effective than tithonia in increasing the labile inorganic P pools but it gave lower maize yields than tithonia which was more effective in reducing the exchangeable Al. It appears that the ability of an OM to lower the exchangeable Al is more important in increasing maize yields than its ability to increase P availability. The effectiveness of the inorganic P sources in increasing maize yields followed the order of their effectiveness in increasing available P, i.e., TSP > MPR > BPR, once Al phytotoxicity was reduced by application of tithonia but the difference between TSP and MPR was not significant. The extra maize yield obtained by the additional 40 kg P ha⁻¹ from the inorganic P sources was, however, in most cases not substantial enough to justify their use. Economic considerations may therefore favour the use of tithonia or FYM when applied alone at 20 kg P ha⁻¹ than when combined with any of the inorganic P sources used in this study at a total P rate of 60 kg ha⁻¹.     

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.     

Recent trends in phosphate balance nationally and by region in Japan

A reduction in chemical phosphate (P) fertilizer application to farmland from 137.6 kg P ha⁻¹ in 1985 to 99.0 kg P ha⁻¹ in 2005 and in manure application from 42.4 kg P ha⁻¹ in 1985 to 32.8 kg P ha⁻¹ in 2005 did not reduce crop P uptake, which averaged 27 kg P ha⁻¹ over the period. Phosphate balance on farmland declined from 153.0 kg P ha⁻¹ in 1985 to 105.4 kg P ha⁻¹ in 2005 while livestock excreta disposal increased from 12.7 kg P ha⁻¹ in 1985 to 23.7 kg P ha⁻¹ in 2005. As a result, residual P associated with agriculture declined from 165.8 kg P ha⁻¹ in 1985 to 129.1 kg P ha⁻¹ in 2005. Phosphate utilization efficiency increased from 15.7% in 1985 to 20.1% in 2005. Median, minimum and maximum values of P flows by region showed similar trends. Phosphate input and withdrawal through crop production by region were not related to regional nitrogen (N) input and withdrawal through crop production. Although non-utilized P associated with agriculture has declined nationally and regionally, it is still higher than that in foreign countries, because of high chemical P fertilizer inputs and low crop yield withdrawal. Because soil P fertility was often sufficiently high previous large P surpluses, reducing P applications did not affect crop yields. Crop P uptake was less than half that of crop N yield. These results indicate that P inputs, especially by chemical fertilizer, for crop production could be reduced, thereby reducing negative environmental effects such as eutrophication of soil and water and conserving limited P resources.     

Combining Tithonia diversifolia and minjingu phosphate rock for improvement of P availability and maize grain yields on a chromic acrisol in Morogoro,Tanzania

A 2-year field experiment was conducted to evaluate the effects of Tithonia diversifolia green manure combined with either Minjingu phosphate rock (MPR) or triple super phosphate (TSP) on soil chemical properties that influence P availability, P pools and maize grain yields, on a Chromic Acrisol in Morogoro, Tanzania. Leafy biomass of tithonia was applied before maize planting for two consecutive growing seasons. Treatments compared were the control, MPR and TSP each at 80 kg P ha⁻¹; tithonia alone at 2.5, 5.0, and 7.5 Mg ha⁻¹ dry matter and tithonia combined with MPR or TSP at 40 kg P ha⁻¹. Tithonia led to significant increases in soil pH, exchangeable Ca, labile (resin and NaHCO₃-Pi), and moderately labile inorganic P (NaOH-Pi). It reduced exchangeable Al and P sorption. Application of MPR alone had liming effects and resulted in increase in labile P. Combining tithonia with MPR had similar but more intense effects. Triple superphosphate alone led to acidification and this was reversed when TSP was co-applied with tithonia. Increasing the application rates of tithonia either alone or in combination with TSP or MPR led to more pronounced liming effects but the differences between 2.5 and 5.0 Mg tithonia ha⁻¹ were not significant due to moisture stress that was experienced during the season. The P and Ca concentrations of the maize plants at tasselling increased with the application of tithonia alone or combined with MPR or TSP, and were significantly correlated with maize grain yields (r = 0.75 and 0.64 for MPR and TSP, respectively). Tithonia added consecutively for 2 years increased total maize grain yields by 70% compared to that in the control. The relative agronomic effectiveness (RAE) of MPR increased from 46% in the first year of application to > 142% in the second year, indicating that the initially slow dissolution of MPR improved by combined application of tithonia and MPR, attributed to reduction of P sorption. It is concluded that tithonia can enhance P availability from the Chromic Acrisol through modification of soil properties associated with P transformation and availability. In cases where tithonia is found within the farmers’ fields its combined application with MPR can increase maize yields at a much-reduced cost associated with tithonia procurement.     

Agronomic and environmental impacts of phosphorus fertilization of low input bahiagrass systems in Florida

Phosphorus management in low input bahiagrass (Paspalum notatum Flugge) systems represents a major challenge of agronomic and environmental importance. Concerns over agricultural P transport to surface waters have prompted several revisions in the P fertilizer recommendations for bahiagrass in Florida. This study evaluated the effects of revised P fertilizer recommendations on forage dry matter yield (DMY) and nutritive value and the potential impacts on water quality in bahiagrass pastures growing on a Spodosol. Treatments consisted of the factorial combination of three N rates (0, 56, and 112 kg N ha⁻¹) and four P rates (0, 5, 10, and 20 kg P ha⁻¹), replicated three times and applied annually in May of 2007 and 2008. Forage was harvested at 28-d intervals and DMY, tissue P and crude protein concentration, and P uptake were measured. To monitor P leaching potential, suction cup lysimeters were installed at 15-, 30-, 60-, 90-, and 150-cm depths. In 2007, bahiagrass DMY was not affected by P; however, in 2008 there was a linear increase in DMY from 6.9 to 8.2 Mg ha⁻¹ as P rate increased. In both years, tissue P increased linearly from 2.1 to 2.5 g kg⁻¹ as P rates increased from 0 to 20 kg P ha⁻¹. Similarly, P uptake increased from 14 kg P ha⁻¹ for the control to 19 kg P ha⁻¹ for the treatment receiving 20 kg P ha⁻¹. During the 2-year study, P fertilization had no impact on soil Mehlich-1, water-extractable P, and leachate P concentrations. Leachate P concentrations at the 15- and 30-cm depths varied seasonally (from 0.05 to 0.85 mg P l⁻¹), with greater spikes occurring during periods of high water table conditions. Current P fertilization recommendation can increase bahiagrass DMY with no adverse impacts on water quality.     

Yield and yield components of cowpea (<Emphasis Type="Italic">Vigna unguiculata</Emphasis> (L.) Walp.) as influenced by Sokoto phosphate rock and placement methods in the semi-arid zone of Nigeria

Phosphate rock with proper management could be a sustainable source of phosphorus for increased cowpea production on the Entisols of Sokoto Semi-arid zone. Therefore, field experiments were conducted in 2004 and 2005 rainy seasons to determine the influence of Sokoto phosphate rock (SPR) and placement methods on the yield of cowpea varieties. Treatments consisted of factorial combination of two varieties (Ba’adare and IAR48), three levels of SPR (25, 50 and 75 kg SPR ha⁻¹) along with a control (0 kg SPR ha⁻¹) and three placement methods (plough sole, broadcast and side-band) laid out in a randomized complete block design replicated 3 times. Results of phosphate rock and placement methods are presented in this paper. The study indicated significant (P < 0.01) response to applied SPR compared to control (1074 kg grain ha⁻¹) in most parameters studied. Application of 25 kg SPR ha⁻¹ significantly (P < 0.05) influenced higher pod yield and number of pods plant⁻¹ only in 2004 trial. But, shelling percentage, grain yield, stover yield, 1000-grain weight, harvest index (HI) and number of seeds pods⁻¹ were not influenced by SPR levels. Significantly (P < 0.05) higher pod yield in 2004, grain yield, 1000-grain weight and number of pods per plant in 2004 and 2005, HI, shelling percentage and number of seeds pod⁻¹ in 2005, were observed in plough-sole than broadcast and band-side methods of fertilizer placement. Therefore, from this study, it was concluded that SPR could be directly used as a source of P to sustain cowpea production (1527 kg grain ha⁻¹ with 25 kg SPR compared to 1074 kg ha⁻¹with 0 kg SPR). Application of 25 kg SPR ha⁻¹ (3.74 kg P ha⁻¹) using plough-sole method of fertilizer placement was most efficient under Sokoto semi-arid condition.     

Grain legume rotation benefits to maize in the northern Guinea savanna of Nigeria: fixed-nitrogen versus other rotation effects

The yield increases often recorded in maize following grain legumes have been attributed to fixed-N and ‘other rotation’ effects, but these effects have rarely been separated. Field trials were conducted between 2003 and 2005 to measure these effects on maize following grain legumes in the northern Guinea savanna of Nigeria. Maize was grown on plots previously cultivated to two genotypes each of soybean (TGx 1448-2E and SAMSOY-2) and cowpea (IT 96D-724 and SAMPEA-7), maize, and natural fallow. The plots were split into four N fertilizer rates (0, 30, 60 and 90 kg N ha⁻¹) in a split plot design. The total effect was calculated as the yield of maize following a legume minus the yield following maize, both without added N and the rotation effect was calculated as the difference between rotations at the highest N fertilizer rate. The legume genotypes fixed between 14 and 51 kg N ha⁻¹ of their total N and had an estimated net N balance ranging from −29.8 to 9.5 kg N ha⁻¹. Positive N balance was obtained only when the nitrogen harvest index was greater than the proportion of N derived from atmosphere. The results also indicated that the magnitude of the fixed-N and other rotation effects varied widely and were influenced by the contributions of the grain legumes to the soil N-balance. In general, fixed-N effects ranged from 124 to 279 kg ha⁻¹ while rotation effects ranged between 193 and 513 kg ha⁻¹. On average, maize following legumes had higher grain yield of 1.2 and 1.3-fold compared with maize after fallow or maize after maize, respectively.     

Interactive effects of selected nutrient resources and tied-ridging on plant growth performance in a semi-arid smallholder farming environment in central Zimbabwe

Crop production in sub-Saharan Africa is constrained by numerous factors including frequent droughts and periods of moisture stress, low soil fertility, and restricted access to mineral fertilisers. A 2 year (2005/6 and 2006/7) field study was conducted in Shurugwi district, central Zimbabwe, to determine the effects of different nutrient resources and two tillage practices on the grain yield of maize (Zea mays L.) and soybean (Glycine max (L.) Merr). Six nutrient resource treatments (control, pit-stored manure, leaf litter, anthill soil, mineral fertiliser, mineral fertiliser plus pit-stored manure) were combined with two tillage practices (conventional tillage and post-emergence tied ridging). Basal fertilisation was done with 0 kg ha⁻¹ as control, 240 kg ha⁻¹ PKS fertiliser, 18 t ha⁻¹ manure, 10 t ha⁻¹ manure plus 240 kg ha⁻¹ PKS fertiliser, 35 t ha⁻¹ leaf litter, 52 t ha⁻¹ anthill soil. About 60 kg N/ha was applied to fertiliser only and fertiliser plus manure treatments as top dressing in the form of ammonium nitrate (34.5%N). A split-plot design was used with nutrient resource as the main plot and tillage practice as the subplot, and five farmers’ fields were used as replicates. Grain yield was determined at physiological maturity (140 and 126 days after planting for maize and soybean, respectively) and adjusted to 12.5% moisture content for maize and 11% for soybean. In the first season (2005/06), addition of different nutrient resources under conventional tillage increased (P < 0.05) maize grain yield by 102–450%, with leaf litter and manure plus fertiliser treatments, giving the lowest (551 kg ha⁻¹⁾ and highest (3,032 kg ha⁻¹) increments, respectively, compared to the control. For each treatment, tied-ridging further increased maize grain yield. For example, for leaf litter, tied-ridging further increased grain yield by 96% indicating the importance of integrating nutrient and water management practices in semi-arid areas where moisture stress is frequent. Despite the low rainfall and extended dry spells in the second season, addition of the different nutrient resources still increased yield which was further increased by tied-ridging in most treatments. Besides providing grain, soybean had higher residual effects on the following maize crop compared to Crotalaria gramiana, a green manure. It was concluded that the highest benefits of tied-ridging, in terms of grain yield, were realised when cattle manure was combined with mineral fertiliser, both of which are available to resource-endowed households. Besides marginally increasing yield, leaf litter and anthill which represent resources that can be accessed by very poor households, have a positive effect of the soil chemical environment.     

Effects of fertilization on nutrient budget and nitrogen use efficiency of farmland soil under different precipitations in Northeastern China

Based on a consecutive 16-year field trial and meteorological data, the effects of fertilization on the nutrient budget and nitrogen use efficiency in farmland soil under different precipitation years were studied. With no fertilization treatment, the grain yield of maize was 3,520 kg ha⁻¹ (mean yield over 13 years). But the maximum yield increased to 7,470 kg ha⁻¹ when treated with mineral N, P and K fertilizers and recycled manure. The nutrient uptake also increased by twofold to threefold in NPKM treated field compared with that in the control treatment. The highest yields were obtained in years with normal precipitation, despite the different fertilization schemes. The lowest yields were obtained in drought or waterlogging years, which were 44.7–58.5% of the yields in years with normal precipitation. It also appeared that the deficits of N, P and K were greater in the years with proper precipitation than those in arid or flood years, because more production was removed from the field. Soil total N decreased significantly when treated with mineral fertilizer or recycled manure alone. The maximum deficit of soil total N was observed in control treatment (557 kg ha⁻¹) from 1990 to 2005. The N treatment resulted in a significant negative balance of P, due to the high yield of the crop in response to applied N. The application of NP or N to soils resulted in a greater negative K balance than that of the control. The greatest negative balance of total P and available P were obtained under the control and N treatment, and the highest deficit of soil total K and exchangeable K were obtained under NP treatment. We found that the rate of 150 kg N ha⁻¹ year⁻¹ was inadequate for maintaining soil N balance, and amendment of soil with organic source could not stop the loss of soil P and K. The applying rates of 150 kg N ha⁻¹ year⁻¹, 25 kg P ha⁻¹ year⁻¹, and 60 kg K ha⁻¹ year⁻¹ combined with 2–3 t ha⁻¹ organic manure were recommended to maintain soil fertility level. The nitrogen use efficiency (NUE) was greatly improved in the years with proper precipitation and balanced fertilization. Higher NUE and grain yields were achieved under NPK and NPKM treatments in years with normal precipitation. The results clearly demonstrated that both organic and mineral fertilizers were needed to increase crop production, improve NUE and maintain soil fertility level.     

Crop production,soil carbon and nutrient balances as affected by fertilisation in a Mollisol agroecosystem

A 19-year field experiment on a Mollisol agroecosystem was carried out to study the productivity of a wheat-maize-soybean rotation and the changes in soil carbon and nutrient status in response to different fertiliser applications in Northeast China. The experiment consisted of seven fertiliser treatments: (1) unfertilised control, (2) annual application of P and K fertilisers, (3) N and K fertilisers, (4) N and P fertilisers, (5) N, P and K fertilisers, (6) N, K and second level P fertilisers, and (7) N, P and second level K fertilisers. Without fertiliser, the Mollisols could support an average yield of 1.88 t ha⁻¹ for wheat, 3.89 t ha⁻¹ for maize and 2.12 t ha⁻¹ for soybean, compared to yields of 3.20, 9.30 and 2.45 t ha⁻¹ respectively for wheat, maize and soybean if the crop nutrient demands were met. At the potential yield level, the N, P and K removal by wheat are 79 kg N ha⁻¹, 15 kg P ha⁻¹, and 53 kg K ha⁻¹, by maize are 207 kg N ha⁻¹, 47 kg P ha⁻¹, and 180 kg K ha⁻¹, by soybean are 174 kg N ha⁻¹, 18 kg P ha⁻¹, and 55 kg K ha⁻¹. Crop yield, change in soil organic carbon (SOC), and the total and available nutrient status were used to evaluate the fertility of this soil over different time periods. This study showed that a fertiliser strategy that was able to maintain yields in the short term (19 years) would not maintain the long term fertility of these soils. Although organic carbon levels did not rise to the level of virgin soil in any treatment, a combination of N, P and K fertiliser that approximated crop export was required to stabilise SOC and prevent a decline in the total store of soil nutrients.     

Managing Legume Cover Crops and their Residues to Enhance Productivity of Degraded Soils in the Humid Tropics: A Case Study in Bukoba District,Tanzania

In degraded soils, establishment of soil-improving legumes can be problematic and requires investment of labour and other resources. We investigated various aspects of managing herbaceous legumes in farmers’ fields in Bukoba District, Tanzania. Biomass and N accumulation by Crotalaria grahamiana was 1.1 Mg ha⁻¹ and 34 kg N ha⁻¹ when established without farmyard manure (FYM) and 3.0 Mg ha⁻¹ and 95 kg N ha⁻¹ when established with 2 Mg FYM ha⁻¹, and incorporation of the biomass gave an increment of 700 kg ha⁻¹ of grain in the subsequent maize crop. Maize grain yield at different application rates of Tephrosia candida residues ranged from 1.4 to 3.3 Mg ha⁻¹ and from 2.0 to 2.8 Mg ha⁻¹ in the high and low rainfall zone, respectively. Application of tephrosia biomass at a rate of 2 Mg ha⁻¹ had no significant effect on maize yield whereas rates of 4, 6 and 8 Mg ha⁻¹ gave comparable yields. Apparent N recovery efficiencies at all rates of tephrosia residues were maximally 27 and 13% for the high and low rainfall zones, respectively. Mulching with Mucuna pruriens suppressed weeds by 49 and 68% and increased maize yield by 57 and 103% compared with the weedy fallow in the respective zones. Incorporated residues had a weaker effect on suppressing weeds and poor labour productivity (2 l and 36 kg grain person-day⁻¹) compared with mulched residues (32 and 52 kg grain person-day⁻¹) in the high and low rainfall zone, respectively. These results indicate that if well managed, legume residues have the potential to increase yields of subsequent maize crops on degraded soils.     

Crop productivity and nutrient use efficiency as affected by long-term fertilisation in North China Plain

Nutrient inputs into crop production systems through fertilisation have come under increased scrutiny in recent years because of reduced nutrient use efficiency and increased environmental impact. Fifteen years of experimental data on dynamics of N, P and K in soil, crop yield and nutrient uptake from nine fertilisation treatments at Zhengzhou, North China Plain, were used to analyse the contribution of different fertilisation treatments to crop yield, nutrient use efficiency and accumulation of nutrients in soil. The results showed that both N and P were limiting factors for crop growth. Without additional N and P fertilisation, only a very low yield level (ca 2 t ha⁻¹ for wheat and 3 t ha⁻¹ for maize) could be maintained. To achieve the potential productivity (i.e. yield level free of water and nutrient stresses) of wheat (6.9 t ha⁻¹) and maize (8.3 t ha⁻¹), wheat would need, on average, 170 kg N ha⁻¹, 32 kg P ha⁻¹ and 130 kg K ha⁻¹, while maize would need 189 kg N ha⁻¹, 34 kg P ha⁻¹ and 212 kg K ha⁻¹. The N and P demands correspond well to the N and P levels supplied in one of the fertilisation treatments (NPK), while K deficiency could occur in the future if no crop residues were returned or no extra K was applied. On average under this NPK treatment, 80% of N and 71% of P could be recovered by the wheat–maize system. Treatments with nutrient inputs higher than the NPK treatment and treatments without combination of N and P have led to accumulation of N and P in the soil profile. The input levels of N and P in the NPK treatment are recommended in fertiliser management, with additional K to avoid future soil K deficiency.     

Soil organic carbon fractions after 16-years of applications of fertilizers and organic manure in a Typic Rhodalfs in semi-arid tropics

Agricultural soils can act as a potential sink of the increased carbon dioxide in the atmosphere if managed properly by application of organic manures and balanced fertilizers. However, the rate of carbon (C) sequestration in soils is low in warm climates and thus the short term changes in soil organic carbon (SOC) contents are almost negligible. Therefore, the knowledge about other C fractions that are more sensitive or responsive and indicative of the early changes in SOC can help to determine the effect of the management practices on soil C sequestration. The objective of this study was to determine the soil C sequestration after 16-years of applications of chemical fertilizers and farmyard manure (FYM) to rice (Oryza sativa)—cowpea (Vigna unguiculata) rotation system in a sandy loam soil (Typic Rhodalfs). The treatments were—(1) one control (no fertilizer or FYM); (2) three chemical fertilizer treatments [100 kg N ha⁻¹ (N), 100 kg N ha⁻¹ + 50 kg P₂O₅ ha⁻¹ (NP), 100 kg N ha⁻¹ + 50 kg P₂O₅ ha⁻¹ + 50 kg K₂O ha⁻¹ (NPK)]; (3) one integrated treatment [(50 kg N ha⁻¹ + 25 kg P₂O₅ ha⁻¹ + 25 K₂O ha⁻¹) + (50 kg N ha⁻¹ from FYM)]; and (4) one organic treatment at10 Mg ha⁻¹ FYM. Compared to the control treatment, the increase in SOC was 36, 33, and 19% greater in organic, integrated, and NPK treatments. The 16-years application of fertilizers and/or FYM resulted in much greater changes in water soluble C (WSC), microbial biomass C (MBC), light fraction of C (LFC), and particulate organic matter (POM) than SOC. Of the SOC, the proportion of POM was highest (24–35%), which was followed by LFC (12–14%), MBC (4.6–6.6%), and WSC (0.6–0.8%). The application of fertilizers and/or FYM increased the mean weight diameter of soil aggregates; thus provided physical protection to SOC from decomposition. Our results suggests that the application of fertilizers and/or FYM helps to sequester C in the soil and that the labile fractions of C can be used as indicators to determine the amount of C sequestered as a result of different management practices.     

Extractable Bray-1 phosphorus and crop yields as influenced by addition of phosphatic fertilizers of various solubilities integrated with manure in an acid soil

Soil extractable Bray-1 P (B1P) and response to phosphate (P) of Setaria anceps cv. Kazungula (Setaria grass) were monitored in a field trial bimonthly for 14 months in an acid soil fertilized with triple super phosphate (TSP), Gafsa phosphate rock (GPR) or Christmas Island phosphate rock (CIPR) integrated with or without manure. Extractable B1P from the same soil incubated with the same fertilizers in wet and dry 3-day cycles for 91 days was determined. Field experimental design was randomized complete block (RCB) with three replications. Results indicated that B1P magnitude for field and incubation trial were; TSP > GPR > CIPR, consistent with their solubility. An integration of manure and fertilizers resulted in much higher extractable B1P than sole fertilizers or manure. Over time, P availability decreased at a fast rate for the first 6 months and later was relatively constant. The dry matter yields (DMYs) exhibited quadratic relationships with P rates. Maximum DMYs (6–11 t ha⁻¹) were attained between 100 and 200 kg P ha⁻¹, above which they declined. Average DMYs were not significantly different for TSP, GPR and CIPR (6.1–6.6 t ha⁻¹). Maximum individual DMY were attained at 2–6 months and then declined to a minimum (2–4 t ha⁻¹) after 1 year. Cumulative yields (20–55 t ha⁻¹) also were not significantly different for the three fertilizers. Manure-CIPR integration increased DMY whilst in GPR and TSP/manure combinations DMYs were depressed. The PRs could supplement the expensive TSP without loss of yields but the non-reactive PR should be integrated with manure.     

Influence of organic amendments on growth, yield and quality of wheat and on soil properties during transition to organic production

A transition period of at least 2 years is required for annual crops before the produce may be certified as organically grown. The purpose of this study was to evaluate the effects of three organic amendments on the yield and quality of wheat (Triticum aestivum L.) and on soil properties during transition to organic production. The organic amendments were composted farmyard manure (FYMC), vermicompost and lantana (Lantana spp. L.) compost applied to soil at four application rates (60 kg N ha⁻¹, 90 kg N ha⁻¹, 120 kg N ha⁻¹ and 150 kg N ha⁻¹). The grain yield of wheat in all the treatments involving organic amendments was markedly lower (36–65% and 23–54% less in the first and second year of transition, respectively) than with the mineral fertilizer treatment. For the organic treatments applied at equivalent N rates, grain yield was higher for FYMC treatment, closely followed by vermicompost. In the first year of transition, protein content of wheat grain was higher (85.9 g kg⁻¹) for mineral fertilizer treatment, whereas, in the second year, there were no significant differences among the mineral fertilizer treatment and the highest application rate (150 kg N ha⁻¹) of three organic amendments. The grain P and K contents were, however, significantly higher for the treatments involving organic amendments than their mineral fertilizer counterpart in both years. Application of organic amendments, irrespective of source and rate, greatly lowered bulk density (1.14–1.25 Mg m⁻³) and enhanced pH (6.0–6.5) and oxidizable organic carbon (13–18.8 g kg⁻¹) of soil compared with mineral fertilizer treatment after a 2-year transition period. Mineral fertilized plots, however, had higher levels of available N and P than plots with organic amendments. All the treatments involving organic amendments, particularly at higher application rates, enhanced soil microbial activities of dehydrogenase, β-glucosidase, urease and phosphatase compared with the mineral fertilizer and unamended check treatments. We conclude that the application rate of 120 kg N ha⁻¹ and 150 kg N ha⁻¹ of all the three sources of organic amendments improved soil properties. There was, however, a 23–65% reduction in wheat yield during the 2 years of transition to organic production.     

Fertilization effects on yield sustainability and soil properties under irrigated wheat–soybean rotation of an Indian Himalayan upper valley

To date, the sustainability of wheat (Triticum aestivum)–soybean (Glycine max) cropping systems has not been well assessed, especially under Indian Himalayas. Research was conducted in 1995–1996 to 2004 at Hawalbagh, India to study the effects of fertilization on yield sustainability of irrigated wheat–soybean system and on selected soil properties. The mean wheat yield under NPK + FYM (farmyard manure) treated plots was ~27% higher than NPK (2.4 Mg ha⁻¹). The residual effect of NPK + FYM caused ~14% increase in soybean yield over NPK (2.18 Mg ha⁻¹). Sustainable yield index values of wheat and the wheat–soybean system were greater with annual fertilizer N or NPK plots 10 Mg ha⁻¹ FYM than NPK alone. However, benefit:cost ratio of fertilization, agronomic efficiency and partial factor productivity of applied nutrients were higher with NPK + FYM than NPK, if FYM nutrients were not considered. Soils under NPK + FYM contained higher soil organic C (SOC), total soil N, total P and Olsen-P by ~10, 42, 52 and 71%, respectively, in the 0–30 cm soil layers, compared with NPK. Non-exchangeable K decreased with time under all treatments except NPK. Total SOC in the 0–30 cm soil layer increased in all fertilized plots. Application of NPK + FYM also improved selected soil physical properties over NPK. The NPK + FYM application had better soil productivity than NPK but was not as economical as NPK if farmers had to purchase manure.     

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.     

Benefits of integrated soil fertility and water management in semi-arid West Africa: an example study in Burkina Faso

The synergistic effect of soil and water conservation (SWC) measures (stone rows or grass strips) and nutrient inputs (organic or mineral nutrient sources) was studied at Saria station, Burkina Faso. The reduction in runoff was 59% in plots with barriers alone, but reached 67% in plots with barriers + mineral N and 84% in plots with barriers + organic N, as compared with the control plots. Plots with no SWC measure lost huge amounts of soil (3 t ha⁻¹) and nutrients. Annual losses from eroded sediments and runoff reached 84 kg OC ha⁻¹, 16.5 kg N ha⁻¹, 2 kg P ha⁻¹, and 1.5 kg K ha⁻¹ in the control plots. The application of compost led to the reduction of total soil loss by 52% in plots without barriers and 79% in plots with stone rows as compared to the losses in control plots. SWC measures without N input did not significantly increase sorghum yield. Application of compost or manure in combination with SWC measures increased sorghum grain yield by about 142% compared to a 65% increase due to mineral fertilizers. Yields increase did not cover annual costs of single SWC measures while application of single compost or urea was cost effective. The combination of SWC measures with application of compost resulted in financial gains of 145,000 to 180,000 FCFA ha⁻¹ year⁻¹ under adequate rainfall condition. Without nutrient inputs, SWC measures hardly affected sorghum yields, and without SWC, fertilizer inputs also had little effect. However, combining SWC and nutrient management caused an increase in sorghum yield.     

Utilization of liquid hog manure to fertilize grasslands in southeast Manitoba: impact of application timing and forage harvest strategy on nutrient utilization and accumulation

Liquid hog manure (LHM) is used to improve productivity of grasslands in western Canada. However, application of manure to meet crop N requirements can result in excessive accumulation of P, especially in grazing systems. A three-year study was carried out to assess the impact of timing of liquid hog manure application and harvest strategy on nutrient utilization and accumulation by grasslands in southeast Manitoba. Liquid hog manure was applied annually at a full rate of 142 ± 20 kg available N ha⁻¹ in spring (Single application) or as two half rate applications of 70 ± 6 kg available N ha⁻¹, one in fall and one in spring (Split application). Two harvest strategies, haying and grazing, were employed to export nutrients from grasslands. Spring-applied manure averaged 8.9% dry matter, 5.7 g total N L⁻¹, 1.5 g total P L⁻¹, and 2.1 g total K L⁻¹ and fall-applied manure from the same source averaged 3.9% dry matter, 4.4 g total N L⁻¹, 0.7 g total P L⁻¹, and 2.2 g total K L⁻¹. Manure application based on grass N requirements resulted in at least two times more P and K applied than recommended for Manitoba grasslands. Nutrient (N, P, and K) export from grasslands was five times higher when grass forage was harvested as hay than through grazing. Average nutrient utilization when forage was harvested as hay was 153 kg N ha⁻¹, 18 kg P ha⁻¹, and 123 kg K ha⁻¹ and was higher in the years with increased precipitation. Grazing was not effective in removing nutrients from grasslands as indicated by lower N, P, and K utilization efficiency (% applied nutrient) in grazed (30% for N, 7% for P, and 18% for K) relative to hayed (75% for N 32% for P, and 103% for K) paddocks. Nutrient accumulation was impacted by a combination of harvest strategy and timing of manure application. Both single and split applications increased soil extractable nutrients, but soil extractable nutrients were higher in grazed relative to hayed paddocks following single manure application. After 3 years of manure application, the amount of Olsen-P (62 kg ha⁻¹) exceeded that required for optimal forage growth. However, soil levels did not exceed the soil Olsen-P regulatory threshold (60 mg kg⁻¹) that restricts manure P applications in Manitoba. An analysis of P balance, for this particular soil, indicated that a surplus of 18.9 kg manure P ha⁻¹ (in excess of forage P exported as hay or weight gain) increased the soil Olsen-P concentration by 1 mg kg⁻¹. Nutrient utilization and accumulation will be impacted by timing of manure application and harvest strategy employed as well as amount of precipitation received during the growing season.     

Nutrient loss pathways from grazed grasslands and the effects of decreasing inputs: experimental results for three soil types

Agriculture is a main contributor of diffuse emissions of N and P to the environment. For N the main loss pathways are NH₃-volatilization, leaching to ground and surface water and N₂(O) emissions. Currently, imposing restraints on farm inputs are used as policy tool to decrease N and P leaching to ground water and to surface water, and the same measure is suggested to combat emissions of N₂O. The response, however, to these measures largely depends on the soil type. In this study nutrient flows of three dairy farms in The Netherlands with comparable intensity on sand, peat and clay soils were monitored for at least 2 years. The first aim was to provide quantitative data on current nutrient loss pathways. The second aim was to explore the responses in partitioning of the nutrient loss pathways when farm inputs were altered. Mean denitrification rates ranged from 103 kg N ha⁻¹ year⁻¹ for the sandy soil to 170 kg N ha⁻¹ year⁻¹ for the peat soil and leaching to surface water was about 73 kg N ha⁻¹ year⁻¹ for the sandy soil, 15 kg N ha⁻¹ year⁻¹ for the clay soil and 38 kg N ha⁻¹ year⁻¹ for the peat soil. For P, leaching to surface water ranged from 2 kg P ha⁻¹ year⁻¹ for the sandy site to 5 kg P ha⁻¹ year⁻¹ for the peat site. The sandy soil was most responsive to changes in N surpluses on leaching to surface water, followed by the peat soil and least responsive was the clay soil. For P, a similar sequence was found. This article demonstrates that similar reductions of N and P inputs result in different responses in N and P loss pathways for different soil types. These differences should be taken into account when evaluating measures to improve environmental performance of (dairy) farms.