Long‐term effects of fertilization on some soil properties under rainfed soybean‐wheat cropping in the Indian Himalayas

This study aims to examine the effects of long‐term fertilization and cropping on some chemical and microbiological properties of the soil in a 32 y old long‐term fertility experiment at Almora (Himalayan region, India) under rainfed soybean‐wheat rotation. Continuous annual application of recommended doses of chemical fertilizer and 10 Mg ha^–1 FYM on fresh‐weight basis (NPK + FYM) to soybean (Glycine max L.) sustained not only higher productivity of soybean and residual wheat (Triticum aestivum L.) crop, but also resulted in build‐up of total soil organic C (SOC), total soil N, P, and K. Concentration of SOC increased by 40% and 70% in the NPK + FYM–treated plots as compared to NPK (43.1 Mg C ha^–1) and unfertilized control plots (35.5 Mg C ha^–1), respectively. Average annual contribution of C input from soybean was 29% and that from wheat was 24% of the harvestable aboveground biomass yield. Annual gross C input and annual rate of total SOC enrichment from initial soil in the 0–15 cm layer were 4362 and 333 kg C ha^–1, respectively, for the plots under NPK + FYM. It was observed that the soils under the unfertilized control, NK and N + FYM treatments, suffered a net annual loss of 5.1, 5.2, and 15.8 kg P ha^–1, respectively, whereas the soils under NP, NPK, and NPK + FYM had net annual gains of 25.3, 18.8, and 16.4 kg P ha^–1, respectively. There was net negative K balance in all the treatments ranging from 6.9 kg ha^–1 y^–1 in NK to 82.4 kg ha^–1 y^–1 in N + FYM–treated plots. The application of NPK + FYM also recorded the highest levels of soil microbial‐biomass C, soil microbial‐biomass N, populations of viable and culturable soil microbes.     

Impact of mineral and organic fertilization on yield,C content in the soil,as well as on C,N and energy balances in a long-term field experiment

Data from a 49-year-long organic–mineral fertilization field experiment with a potato–maize–maize–wheat–wheat crop rotation were used to analyse the impact of different fertilizer variations on yield ability, soil organic carbon content (SOC), N and C balances, as well as on some characteristic energy balance parameters. Among the treatments, the fertilization variant with 87 kg ha^?1 year^?1 N proved to be economically optimal (94% of the maximum). Approximately 40 years after initiation of the experiment, supposed steady-state SOC content has been reached, with a value of 0.81% in the upper soil layer of the unfertilized control plot. Farmyard manure (FYM) treatments resulted in 10% higher SOC content compared with equivalent NPK fertilizer doses. The best C balances were obtained with exclusive mineral fertilization variants (?3.8 and ?3.7 t ha^?1 year^?1, respectively). N uptake in the unfertilized control plot suggested an airborne N input of 48 kg ha^?1 year^?1. The optimum fertilizer variant (70 t ha^?1 FYM-equivalent NPK) proved favourable with a view to energy. The energy gain by exclusive FYM treatments was lower than with sole NPK fertilization. Best energy intensity values were obtained with lower mineral fertilization and FYM variants. The order of energy conversion according to the different crops was maize, wheat and potato.     

Effect of long‐term fertilization and manuring on potassium release properties in a Typic Ustochrept

A long‐term fertilizer experiment, over 27 years, studied the effect of mineral fertilizers and organic manures on potassium (K) balances and K release properties in maize‐wheat‐cowpea (fodder) cropping system on a Typic Ustochrept. The treatments consisted of control, 100% nitrogen (100% N), 100% nitrogen and phosphorus (100% NP), 50% nitrogen, phosphorus, and potassium (50% NPK), 100% nitrogen, phosphorus, and potassium (100% NPK), 150% nitrogen, phosphorus, and potassium (150% NPK), and 100% NPK+farmyard manure (100% NPK+FYM). Nutrients N, P, and K in 100% NPK treatment were applied at N: 120 kg ha^—1, P: 26 kg ha^—1, and K: 33 kg ha^—1 each to maize and wheat crops and N: 20 kg ha^—1, P: 17 kg ha^—1, and K: 17 kg ha^—1 to cowpea (fodder). In all the fertilizer and manure treatments removal of K in the crop exceeded K additions and the total soil K balance was negative. The neutral 1 N ammonium acetate‐extractable K in the surface soil (0—15 cm) ranged from 0.19 to 0.39 cmol kg^—1 in various treatments after 27 crop cycles. The highest and lowest values were obtained in 100% NPK+FYM and 100% NP treatments, respectively. Non‐exchangeable K was also depleted more in the treatments without K fertilization (control, 100% N, and 100% NP). Parabolic diffusion equation could describe the reaction rates in CaCl₂ solutions. Release rate constants (b) of non‐exchangeable K for different depth of soil profile showed the variations among the treatments indicating that long‐term cropping with different rates of fertilizers and manures influenced the rate of K release from non‐exchangeable fraction of soil. The b values were lowest in 100% NP and highest in 100% NPK+FYM treatment in the surface soil. In the sub‐surface soil layers (15—30 and 30—45 cm) also the higher release rates were obtained in the treatments supplied with K than without K fertilization indicating that the sub‐soils were also stressed for K in these treatments.     

Long-term yield trend and sustainability of rainfed soybean–wheat system through farmyard manure application in a sandy loam soil of the Indian Himalayas

A long-term (30 years) soybean–wheat experiment was conducted at Hawalbagh, Almora, India to study the effects of organic and inorganic sources of nutrients on grain yield trends of rainfed soybean (Glycine max)–wheat (Triticum aestivum) system and nutrient status (soil C, N, P and K) in a sandy loam soil (Typic Haplaquept). The unfertilized plot supported 0.56 Mg ha⁻¹ of soybean yield and 0.71 Mg ha⁻¹ of wheat yield (average yield of 30 years). Soybean responded to inorganic NPK application and the yield increased significantly to 0.87 Mg ha⁻¹ with NPK. Maximum yields of soybean (2.84 Mg ha⁻¹) and residual wheat (1.88 Mg ha⁻¹) were obtained in the plots under NPK + farmyard manure (FYM) treatment, which were significantly higher than yields observed under other treatments. Soybean yields in the plots under the unfertilized and the inorganic fertilizer treatments decreased with time, whereas yields increased significantly in the plots under N + FYM and NPK + FYM treatments. At the end of 30 years, total soil organic C (SOC) and total N concentrations increased in all the treatments. Soils under NPK + FYM-treated plots contained higher SOC and total N by 89 and 58% in the 0–45 cm soil layer, respectively, over that of the initial status. Hence, the decline in yields might be due to decline in available P and K status of soil. Combined use of NPK and FYM increased SOC, oxidizable SOC, total N, total P, Olsen P, and ammonium acetate exchangeable K by 37.8, 42.0, 20.8, 30.2, 25.0, and 52.7%, respectively, at 0–45 cm soil layer compared to application of NPK through inorganic fertilizers. However, the soil profiles under all the treatments had a net loss of nonexchangeable K, ranging from 172 kg ha⁻¹ under treatment NK to a maximum of 960 kg ha⁻¹ under NPK + FYM after 30 years of cropping. Depletion of available P and K might have contributed to the soybean yield decline in treatments where manure was not applied. The study also showed that although the combined NPK and FYM application sustained long-term productivity of the soybean–wheat system, increased K input is required to maintain soil nonexchangeable K level.     

Wirkung der Phosphatdüngung in einem 40jährigen Dauerversuch auf einer Sandlöß-Braunschwarzerde in Halle

Effect of differential P fertilizer application over a period of 40 years in a long-term field experiment on a Phaeozem near Halle, Germany P fertilizer in three forms was applied at 0 (P₀), 15 (P₁) and 45 (P³) kg ha^?1 P per annum to a relation lucerne — lucerne — potatoes — winter rye — sugar beet — spring barley. The experiment was laid down in 1949 near Halle on Phaeozem soil containing 57 mg total P and 8.5 mg DL-P per 100 g soil (0–20 cm) and with pH 6.0 (0.1 M KCl). Small differences between treatments were first observed only after 20 years. Since then the effects of treatment increased but even after the 7th cycle (1982–1987) the maximum effect was <8 cereal units (CU) per ha. The crops most responsive to P were: lucerne (in the year of sowing), potatoes and sugar beet. Over the period 1977–1988, annual P removal exceeded P input by 23 and 9 kg ha^?1 P for treatments P₀ and P₁ respectively; on treatment P³, P input exceeded removal by 19 kg ha^?1 per annum. DL-P on treatment P₀ in 1979 was 3.5–4.0 mg per 100 g, insufficient to support high yields. A level of 5–6 mg DL-P per 100 g soil, as found in treatment P₁ is required for sustainable high yield. Change in total soil P content corresponded with the P balance (input — withdrawal) only on treatment P³. The lack of correspondence on treatments P₀ and P₁ suggests that crops obtained much of their P requirement from subsoil.     

Evaluation of White yam (Dioscorea rotundata) genotypes for arbuscular mycorrhizal colonization,leaf nutrient concentrations and tuber yield under NPK fertilizer application

Yield decline in yam may not only be due to soil nutrient depletion but also to the activity of soil microflora. Arbuscular mycorrhizal (AM) symbiosis helps in plant nutrition but may be affected by the application of fertilizer. The effects of nitrogen (N), phosphorus (P), and potassium (K) fertilizer rates on the AM colonization, leaf nutrient concentrations, and tuber yields of eleven genotypes of Dioscorea rotundata were investigated at Ibadan, Nigeria. The soil was ferric luvisol. Eleven genotypes were selected from the previously conducted screening of 75 genotypes of D. rotundata for fertilizer response. Four application rates: 0, 200, 400, and 600 kg ha^?1 of NPK 15-15-15 were applied in a split plot design with four replications. Fertilizer rate was the main plot and variety was the sub plot. Percentage AM colonization was significantly reduced at 600 kg ha^?1 but not at lower rates when compared to zero rate and it was negatively correlated with leaf N, P, and zinc (Zn) concentrations. Leaf N concentrations were significantly increased at 200 kg ha^?1 in five genotypes and at 600 kg ha^?1 in two genotypes compared to zero application. Leaf P and K concentrations were decreased with the application of fertilizer in most of the genotypes. The NPK fertilizer of 15-15-15 at the rate of 200–400 kg ha^?1 gave yield response in eight genotypes of D. rotundata, with minimal or no effect on their AM colonization when compared to zero application. Long term study on the effect of fertilizer application on AM symbiosis in yam is recommended.     

Effects of humus content,farmyard manuring,and mineral‐N fertilization on yields and soil properties in a long‐term trial

Investigations carried out at Field F3 of the Halle long‐term fertilization trials using data from 1974 to 1983 showed that with adequate supply of mineral N‐fertilizer soil organic matter (SOM) had no significant effects of yield. Similarly enhanced SOM did not justify a reduction of mineral N (Stumpe et al., 2000). The studies presented here examine the effects of the SOM differences existing after the termination of those trials in 1986 up until 1997 (then mainly differences of hardly decomposable SOM) in comparison to farmyard manuring with enhanced mineral N application (3‐factor‐experiment). As with total SOM, hardly decomposable SOM did not directly affect yields. The effects of FYM treatment observed at lower mineral‐N levels were compensated for by enhanced mineral‐N supply. The direct effect of FYM (40 t ha^—1) corresponded to a mineral‐N supply of about 60 kg ha^—1 and the residual effect to about 20 kg ha^—1. The differences of the C‐content in the soil at the beginning of the present studies continued throughout the experimental period of 12 years. In addition, significant differentiation has been caused by FYM and N fertilization in comparison to unfertilized treatments. The major finding is that differences in SOM content do not lead to yield differences on physically good soils (chernozem‐like soils) if appropriate compensation by mineral‐N fertilization takes place.     

A lysimeter study of the fate of fertilizer nitrogen in spring barley crops grown on a shallow soil overlying Chalk: denitrification losses and the nitrogen balance

Four successive spring barley crops were grown in monoliths of a shallow soil overlying Chalk, contained in lysimeters. After harvest of the fourth crop, 25% of the nitrogen-15 labelled fertilizer applied 4 years earlier was found remaining in the roots and soil. Of this, 73% was present in the upper 30cm of the profile. From the amounts of fertilizer derived nitrogen that remained at the beginning of each cropping season we estimate that 5–6% of the residual nitrogen-15 turned over each year, representing a net release of 20% of the labelled nitrogen contained in the microbial biomass. Mineralization of the total biomass at the same fractional rate would release 120 kg N ha^?1 a^?1. This estimate is supported by the difference between input and outputs of total nitrogen during the experiment of 76–94 kg N ha^?1 a^?1 in fertilized lysimeters and 129kg N ha^?1 a^?1 in unfertilized control lysimeters. The total recovery of the applied labelled nitrogen was 81–87%. The nitrogen not accounted for was taken to be lost by denitrification of nitrate to dinitrogen, as no nitrous oxide emissions were detected during the experiment. Laboratory studies in aerobic and anaerobic conditions in presence of acetylene confirmed that 10–20% of the applied nitrogen-15 could have been transformed to dinitrogen.     

Fate of residual 15N-labeled fertilizer in dryland farming systems on soils of contrasting fertility

Abstract

Up to 50% of nitrogen (N) fertilizer can remain in soil after crop harvest in dryland farming. Understanding the fate of this residual fertilizer N in soil is important for evaluating its overall use efficiency and environmental effect. Nitrogen-15 (¹⁵N)-labeled urea (165 kg N ha^?1) was applied to winter wheat (Triticum aestivum L.) growing in three different fertilized soils (no fertilizer, No-F; inorganic nitrogen, phosphorus and potassium fertilization, NPK; and manure plus inorganic NPK fertilization, MNPK) from a long-term trial (19 years) on the south of the Loess Plateau, China. The fate of residual fertilizer N in soils over summer fallow and the second winter wheat growing season was examined. The amount of the residual fertilizer N was highest in the No-F soil (116 kg ha^?1), and next was NPK soil (60 kg ha^?1), then the MNPK soil (43 kg ha^?1) after the first winter wheat harvest. The residual fertilizer N in the No-F soil was mainly in mineral form (43% of the residual ¹⁵N), and for the NPK and MNPK soils, it was mainly in organic form. The loss rate of residual ¹⁵N in No-F soil over summer fallow was as high as 48%, and significantly (P < 0.05) higher than that in the NPK soil (22%) and MNPK soil (19%). The residual ¹⁵N use efficiency (RNUE) by the second winter wheat was 13% in the No-F soil, 6% in the NPK soil and 8% in the MNPK soil. These were equivalent to 9.0, 2.0 and 2.2% of applied ¹⁵N. The total ¹⁵N recovery (¹⁵N uptake by crops and residual in 0–100 cm soil layer) in the MNPK and NPK soils (84.5% and 86.6%, respectively) were both significantly higher than that in the No-F soil (59%) after two growing seasons. The ¹⁵N uptake by wheat in two growing seasons was higher in the MNPK soil than in NPK soil. Therefore, we conclude that a high proportion of the residual ¹⁵N was lost during the summer fallow under different land management in dryland farming, and that long-term combined application of manure with inorganic fertilizer could increase the fertilizer N uptake and decrease N loss.     

Long-term effects of fertilization and manuring on productivity and soil biological properties under rice (Oryza sativa)–wheat (Triticum aestivum) sequence in Mollisols

Long-term effects of chemical fertilizers and farmyard manure (FYM) in rice (Oryza sativa)–wheat (Triticum aestivum) cropping system were monitored for two consecutive years after 38 and 39 years on productivity and soil biological properties of Mollisols. The study encompasses varying chemical fertilizer levels of optimum fertilizer rate (120, 26 and 37 kg ha^?1 N, P and K, respectively) for both the crops. The treatments were application of 50% NPK, 100% NPK, 150% NPK, 100% NPK + hand weeding (HW), 100% NPK + Zn, 100% NP, 100% N, 100% NPK + 15 t FYM ha^?1, 100% NPK(-S) and unfertilized control. The rice and wheat yields were highest with 100% NPK + 15 t FYM ha^?1. This treatment also gave maximum and significantly more counts of bacteria, fungi and actinomycetes in soil than all the other treatments after crop harvest. The soil microbial biomass C (410.0 and 407.5 µg g^?1) and N (44.53 and 48.30 µg g^?1) after rice and wheat, respectively, were highest with 100% NPK + 15 t FYM ha^?1, which were significantly higher over all the other treatments. The activities of soil enzymes like dehydrogenase, acid and alkaline phosphatase, arylsulphatase and urease and CO₂ evolution rate with 100% NPK + 15 t FYM ha^?1 were also found significantly higher over the other treatments. Fertilizer treatments with 100% NPK and 150% NPK were comparable and significantly better than application of 50% NPK, 100% N, 100% NP and 100% NPK(-S) in various studied soil biological properties. Integrated use of 100% NPK with FYM sustained the higher yields and soil biological properties under rice–wheat cropping system in Mollisols. Application of Zn and hand weeding with 100% NPK were found better over 100% NPK alone in rice and wheat productivity. Imbalanced use of chemical fertilizers had the harmful effect on soil biological health.     

Effect of P‐solubilizing Azotobacter chroococcum on N,P, K uptake in P‐responsive wheat genotypes grown under greenhouse conditions

Natural and mutant strains of A. chroococcum were isolated from Indian soils. Their ability to dissolve phosphate and their phytohormone production were tested under in vitro conditions. In addition the effect of bacterial inoculation of Azotobacter on N, P, K uptake by three P responsive wheat genotypes (Triticum aestivum L.) under greenhouse conditions at five nutrient levels (Control, 90 kg N ha^—1, 90 kg N + 26 kg P ha^—1, 120 kg N ha^—1 and 120 kg N + 26 kg P ha^—1) was studied. In vitro phosphate solubilization and growth hormone production by mutant strains was more than by the soil isolates. Inoculation of wheat varieties with the soil isolates and mutant strains of A. chroococcum showed greater NPK uptakes as compared with parent soil isolates. Mutant strains M15 and M37 were proved to be the most effective for all three wheat varieties with regard to NPK uptake as well as root biomass production under greenhouse conditions.     

Influence of Soil and Fertilizer Nutrients on Sustainability of Rainfed Finger Millet Yield and Soil Fertility in Semi-arid Alfisols

Productivity of rainfed finger millet in semiarid tropical Alfisols is predominantly constrained by erratic rainfall, limited soil moisture, low soil fertility, and less fertilizer use by the poor farmers. In order to identify the efficient nutrient use treatment for ensuring higher yield, higher sustainability, and improved soil fertility, long term field experiments were conducted during 1984 to 2008 in a permanent site under rainfed semi-arid tropical Alfisol at Bangalore in Southern India. The experiment had two blocks—Farm Yard Manure (FYM) and Maize Residue (MR) with 5 fertilizer treatments, namely: control, FYM at 10 t ha^?1, FYM at 10 t ha^?1 + 50% NPK [nitrogen (N), phosphorus (P), potassium (K)], FYM at 10 t ha^?1 + 100% NPK (50 kg N + 50 kg P + 25 kg K ha^?1) and 100% NPK in FYM block; and control, MR at 5 t ha^?1, MR at 5 t ha^?1 + 50% NPK, MR at 5 t ha^?1 + 100% NPK and 100% NPK in MR block. The treatments differed significantly from each other at p < 0.01 level of probability in influencing finger millet grain yield, soil N, P, and K in different years. Application of FYM at 10 t ha^?1 + 100% NPK gave a significantly higher yield ranging from 1821 to 4552 kg ha^?1 with a mean of 3167 kg ha^?1 and variation of 22.7%, while application of maize residue at 5 t ha^?1 + 100% NPK gave a yield of 593 to 4591 kg ha^?1 with a mean of 2518 kg ha^?1 and variation of 39.3% over years. In FYM block, FYM at 10 t ha^?1 + 100% NPK gave a significantly higher organic carbon (0.45%), available N (204 kg ha^?1), available P (68.6 kg ha^?1), and available K (107 kg ha^?1) over years. In maize residue block, application of MR at 5 t ha^?1 + 100% NPK gave a significantly higher organic carbon (0.39%), available soil N (190 kg ha^?1), available soil P (47.5 kg ha^?1), and available soil K (86 kg ha^?1). The regression model (1) of yield as a function of seasonal rainfall, organic carbon, and soil P and K nutrients gave a predictability in the range of 0.19 under FYM at 10 t ha^?1 to 0.51 under 100% NPK in FYM block compared to 0.30 under 100% NPK to 0.67 under MR at 5 t ha^?1 application in MR block. The regression model (2) of yield as a function of seasonal rainfall, soil N, P, and K nutrients gave a predictability in the range of 0.11 under FYM at 10 t ha^?1 to 0.52 under 100% NPK in FYM block compared to 0.18 under MR at 5 t ha^?1 + 50% NPK to 0.60 under MR at 5 t ha^?1 application in MR block. An assessment of yield sustainability under different crop seasonal rainfall situations indicated that FYM at 10 t ha^?1 + 100% NPK was efficient in FYM block with a maximum Sustainability Yield Index (SYI) of 41.4% in <500 mm, 64.7% in 500–750 mm, 60.2% in 750–1000 mm and 60.4% in 1000–1250 mm rainfall, while MR at 5 t ha^?1 + 100% NPK was efficient with SYI of 29.6% in <500 mm, 50.2% in 500–750 mm, 40.6% in 750–1000 mm, and 39.7% in 1000–1250 mm rainfall in semi-arid Alfisols. Thus, the results obtained from these long term studies incurring huge expenditure provide very good conjunctive nutrient use options with good conformity for different rainfall situations of rainfed semiarid tropical Alfisol soils for ensuring higher finger millet yield, maintaining higher SYI, and maintaining improved soil fertility.     

Evaluating Inorganic Nitrogen and Rye-Crimson Clover Mixture Fertilization of Spring Broccoli and Lettuce by 15Nitrogen Tracing and Mass Balance

ABSTRACT

Broccoli (Brassica oleraceaL. var. italica) and lettuce (Latuca sativaL.) were grown under greenhouse conditions with nitrogen (N) from a cover crop mixture of rye (Secale cerealeL.) and crimson clover (Trifolium incarnatumL.) and ammonium nitrate (NH₄NO₃). Individual cover crop species were produced with non-enriched or enriched (5 atom % NH₄ ¹⁵NO₃) Hoagland Nutrient Solutions resulting in enriched rye [0.799% atom % ¹⁵N, 24:1 carbon (C):N ratio] and enriched clover (0.686% atom % ¹⁵N, 19:1 C:N ratio). Cover crops were applied as an equal mixture of rye and clover at 1884, 3768, and 5652 kg·ha^{? 1} dry weight to supply 26, 52, and 78 kg·ha^{? 1} N. Enriched materials were only applied at the 3768 kg·ha^{? 1} rate, either as enriched rye plus non-enriched clover or non-enriched rye plus enriched clover. Additional treatments consisted of an unfertilized control and three NH₄NO₃ fertilizer rates; 112, 224, and 336 kg·ha^{? 1} N for broccoli and 70, 140, and 210 kg·ha^{? 1} N for lettuce. Combination treatments were the standard cover crop rate (3768 kg·ha^{? 1}) plus the lowest N fertilizer rate for each vegetable. Cover crops did not increase yield of either broccoli or lettuce, and contributed only 17% of the N in broccoli and 15% of the N in lettuce. The majority of cover crop ¹⁵N remained in the soil: 54.8% and 81.3% of rye and clover N, respectively, after broccoli harvest; and 68.1% and 79.2% of rye and clover N, respectively, after lettuce harvest. Broccoli plant tissue recoveries were 8.0% of the rye and 11.0 % of the clover ¹⁵N; while lettuce plant tissue recoveries were 6.3% (rye) and 4.1% (clover). Broccoli yield could not be assessed due to lack of floret development, but dry matter accumulation was maximized at 224 kg·ha^{? 1}N. Lettuce yield and fertilizer N recovery efficiency (by mass balance) was maximized at 140 g·ha^{? 1} N.     

Long‐term application of biowaste compost versus mineral fertilization: Effects on the nutrient and heavy metal contents of soil and plants

In recent years the use of biowaste compost (BC) as a soil amendment is of increasing interest. The aim of the experiment was to investigate the influence of different fertilization systems: biowaste compost, annual average of 32 Mg ha^—1 BC (fresh matter) and mineral fertilizer (83:52:95 kg ha^—1 NPK fertilizer) on the nutrient and heavy metal contents of soil and plants. Soil samples (1997) and harvest products (1996—1998) from a field trial (initiated 1992) were analyzed for K, Mg, P, Cu, Mn, Mo, Zn, Cd, Ni, and Pb. The five‐year fertilization with composted biowaste did not influence the total contents of Cd, Mn, Mo, and Ni in soil. The total soil contents of Zn and Pb were significantly higher in soils of the BC treatment than in the unfertilized control. Both fertilized plots tended to have higher Cu and Zn contents in harvest products than the unfertilized control. The mineral fertilization inhibited the Mo uptake by plants. In 1998 the mineral fertilization led to higher, and the biowaste compost application to lower, Cd contents in potato tubers as compared to the control.     

Fate of fertilizer nitrogen.

Results are presented from a three year lysimeter investigation, employing single (¹⁵NH₄NO₃) and double (¹⁵NH₄¹⁵NO₃) labelled ammonium nitrate to study the uptake of soil and fertilizer nitrogen by cut ryegrass at 250, 500 and 900 kg N ha^?1 a^?1. Average annual recoveries of nitrogen were equivalent to 99,76 and 50% of the nitrogen added at 250, 500 and 900 kg N ha^?1, respectively. At 250 kg N ha^?1 the difference between the overall nitrogen recovery and the fertilizer recovery was almost entirely attributable to pool substitution resulting from mineralization/immobilization turnover (MIT). At 900 kg N ha^?1 both the low overall recovery of nitrogen and the low fertilizer recovery reflected the large excess of available nitrogen over crop requirements. No evidence of ‘priming’ was obtained. Analysis of the results from single and double labelled lysimeters using simultaneous equations indicated that at 250 kg N ha^?1,～70% of the nitrogen in the crop was derived from the ammonium pool. At 500 kg N ha^?1 this dropped to 64%, while at 900 kg N ha^?1 the figure was 59%. There was a suggestion that at the lower application rates, preferential uptake of ammonium was occurring but that as N supply exceeded crop requirements, nitrate was the major N source. Despite the preferential exploitation of the ammonium pool, at 250 and 500 kg N ha^?1 pool substitution resulting from MIT resulted in lower recoveries of fertilizer ammonium compared with fertilizer nitrate.     

Effects of leguminous plant residues and NPK fertilizer application on the performance of yam (Dioscorea rotundata ‘c.v.’ ewuru) in south-western Nigeria

The effects of cultivating and incorporating residues of previous tropical kudzu (Pueraria phaseoloides) and soybean (Glycine max) with application of NPK fertilizer on yam performance were evaluated at the teaching and research farm, LAUTECH, Nigeria. There were nine treatments: incorporation of legume residues (5 t DM ha^?1), application of recommended fertilizer rate for yam (90–50–75 kg NPK ha^?1) in the zone or 50% of recommended rate (45–25–37.5 kg NPK ha^?1), alone and in combination with residues and a control without residues or fertilizer in a randomized complete block design. Cultivation of previous legumes reduced soil nematode population (>200%) compared with no legumes. For both years, application of Pueraria residues improved tuber yield by an average of 15.8% compared with control. Fertilizer application enhanced arbuscular mycorrhizal (AM) colonization of yam roots but AM colonization was lower (～50%) in plots where Pueraria residues were incorporated compared with other plots. Combined application of plant residues with fertilizer improved soil organic carbon, total N, exchangeable Ca and Mg compared with application of NPK fertilizer. From these results, it is concluded that half of the recommended NPK rate may be adequate and incorporation of residues with reduced NPK fertilizer application may be a sustainable soil fertility management option for continuous yam production.     

Mechanisms of soil N dynamics following long-term application of organic fertilizers to subtropical rain-fed purple soil in China

In this study, a ¹⁵N tracing incubation experiment and an in situ monitoring study were combined to investigate the effects of different N fertilizer regimes on the mechanisms of soil N dynamics from a long-term repeated N application experiment. The field study was initiated in 2003 under a wheat-maize rotation system in the subtropical rain-fed purple soil region of China. The experiment included six fertilization treatments applied on an equivalent N basis (280 kg N ha⁻¹), except for the residue only treatment which received 112 kg N ha⁻¹: (1) UC, unfertilized control; (2) NPK, mineral fertilizer NPK; (3) OM, pig manure; (4) OM-NPK, pig manure (40% of applied N) with mineral NPK (60% of applied N); (5) RSD, crop straw; (6) RSD-NPK, crop straw (40% of applied N) with mineral NPK (60% of applied N). The results showed that long-term repeated applications of mineral or organic N fertilizer significantly stimulated soil gross N mineralization rates, which was associated with enhanced soil C and N contents following the application of N fertilizer. The crop N offtake and yield were positively correlated with gross mineralization. Gross autotrophic nitrification rates were enhanced by approximately 2.5-fold in the NPK, OM, OM-NPK, and RSD-NPK treatments, and to a lesser extent by RSD application, compared to the UC. A significant positive relationship between gross nitrification rates and cumulative N loss via interflow and runoff indicated that the mechanisms responsible for increasing N loss following long-term applications of N fertilizer were governed by the nitrification dynamics. Organic fertilizers stimulated gross ammonium (NH₄⁺) immobilization rates and caused a strong competition with nitrifiers for NH₄⁺, thus preventing a build-up of nitrate (NO₃⁻). Overall, in this study, we found that partial or complete substitution of NPK fertilizers with organic fertilizers can reduce N losses and maintain high crop production, except for the treatment involving application of RSD alone. Therefore, based on the N transformation dynamics observed in this study, organic fertilizers in combination with mineral fertilizer applications (i.e. OM, OM-NPK, and RSD-NPK treatments) are recommended for crop production in the subtropical rain-fed purple soils in China.     

Effects of NPK fertilizer combinations on yield and nitrogen balance in sorghum or pigeonpea on a vertisol in the semi-arid tropics

A long-term experiment was carried out on a Vertisol from 1986 to 1992 to examine the combined effects of NPK fertilizers on yield using sorghum (Sorghum bicolor L. Moench cv. CSH 5) and short-duration pigeonpea (Cajanus cajan L. Millsp. cv. ICPL 87). The fertilizer treatments were as follows: 0 (no fertilization), N (150 kg N ha^-1 ), P (65.5 kg P₂O₅ ha^-1), K (124.5 kg K₂O ha^-1), and all possible combinations (NP, NK, PK, and NPK). In this study we continued this experiment during the period 1993 to 1994 and analyzed the crop yield response to fertilizers and the N balance. The amount of N derived from the atmosphere and fertilizer was estimated by the ¹⁵N natural abundance method and ^l5N isotope dilution method, respectively. A combined application of Nand P fertilizers gave the highest grain yield for the two crops under the 8th and 9th continuous croppings, unlike the application of K fertilizer. The values of total N for the two crops were significantly higher in the NP and NPK plots. These crops took up N mainly from soil. There was a significant positive relationship between the uptake of N_dff and N_dfs by each crop. Pigeonpea or sorghum took up more N from the soil in the N fertilizer plots than in the plots without N, suggesting that soil N fertility was enhanced and the amount of N supplied from soil increased in the plots with consecutive application of N fertilizer for 7 y. Even pigeonpea, which fixes atmospheric N inherently, needed N fertilizer to achieve high grain yield, suggesting that N fixation by the nodules was not always sufficient to meet the N requirements of the crop under these conditions. Although fertilizer N exerted a beneficial effect on plant growth and yield in the two crops, the values of fertilizer N recovery (FNR) by the two crops were considerably low. Therefore, it is suggested that the development of N fertilizer management which could maximize FNR of each crop should be promoted.     

Cover crop nitrogen availability to conventional and no‐till corn: Soil mineral nitrogen,corn nitrogen status,and corn yield

Abstract

Understanding seasonal soil nitrogen (N) availability patterns is necessary to assess corn (Zea mays L.) N needs following winter cover cropping. Therefore, a field study was initiated to track N availability for corn in conventional and no‐till systems and to determine the accuracy of several methods for assessing and predicting N availability for corn grown in cover crop systems. The experimental design was a systematic split‐split plot with fallow, hairy vetch (Vicia villosa Roth), rye (Secale cereale L.), wheat (Triticum aestivum L.), rye+hairy vetch, and wheat+hairy vetch established as main plots and managed for conventional till and no‐till corn (split plots) to provide a range of soil N availability. The split‐split plot treatment was sidedressed with fertilizer N to give five N rates ranging from 0–300 kg N ha^‐1 in 75 kg N ha^‐1 increments. Soil and corn were sampled throughout the growing season in the 0 kg N ha^‐1 check plots and corn grain yields were determined in all plots. Plant‐available N was greater following cover crops that contained hairy vetch, but tillage had no consistent affect on N availability. Corn grain yields were higher following hairy vetch with or without supplemental fertilizer N and averaged 11.6 Mg ha^‐1 and 9.9 Mg ha^‐1 following cover crops with and without hairy vetch, respectively. All cover crop by tillage treatment combinations responded to fertilizer N rate both years, but the presence of hairy vetch seldom reduced predicted fertilizer N need. Instead, hairy vetch in monoculture or biculture seemed to add to corn yield potential by an average of about 1.7 Mg ha^‐1 (averaged over fertilizer N rates). Cover crop N contributions to corn varied considerably, likely due to cover crop N content and C:N ratio, residue management, climate, soil type, and the method used to assess and assign an N credit. The pre‐sidedress soil nitrate test (PSNT) accurately predicted fertilizer N responsive and N nonresponsive cover crop‐corn systems, but inorganic soil N concentrations within the PSNT critical inorganic soil N concentration range were not detected in this study.     

Assessment of cowpea and groundnut contributions to soil fertility and succeeding sorghum yields in the Guinean savannah zone of Burkina Faso (West Africa)

Atmospheric biological nitrogen fixation (BNF) by cowpea (Vigna unguiculata) and groundnut (Arachis hypogea) was evaluated using a 2-year (2000–2001) experiment with different fertilizer treatments. The ¹⁵N isotopic dilution method with a nonfixing cowpea as test reference crop was used. The effects of the two legumes on soil N availability and succeeding sorghum (Sorghum bicolor) yields were measured. Groundnut was found to fix 8 to 23 kg N ha-1 and the percentage of N derived from the atmosphere varied from 27 to 34%. Cowpea fixed 50 to 115 kg N ha⁻¹ and the percentage of N derived from the atmosphere varied from 52 to 56%. Compared to mineral NPK fertilizer alone, legumes fixed more N from the atmosphere when dolomite or manure was associated with mineral fertilizers. Compared to soluble phosphate, phosphate rock increased BNF by cowpea. Significant correlation (p<0.05, R ²=0.94) was observed between total N yields of legumes and total N derived from the atmosphere. Compared to monocropping of sorghum, the soils of cowpea–sorghum and groundnut–sorghum rotations increased soil mineral N from 15 and 22 kg N ha⁻¹, respectively. Cowpea–sorghum and groundnut–sorghum rotations doubled N uptake and increased succeeding sorghum yields by 290 and 310%, respectively. Results suggested that, despite their ability to fix atmospheric nitrogen, N containing fertilizers (NPK) are recommended for the two legumes. The applications of NPK associated with dolomite or cattle manure or NK fertilizer associated with phosphate rock were the better recommendations that improved BNF, legumes, and succeeding sorghum yields.