Long-term Soil Fertility Experiments Research Articles

Where does all the phosphorus go? Mass balance modelling of phosphorus in the Swedish long-term soil fertility experiments

To gain insights into phosphorus (P) dynamics in soils and the ability to predict soil responses to varying fertilizer inputs, mass balance models prove to be valuable tools. In this study, a new dynamic mass balance model, PBalD8, was used to describe the change in extracted P in the A horizon of soils subjected to diverse fertilizer treatments over a period of 50 to 60 years in five soil fertility experiments. The model employed a Freundlich equation to describe soil-solution partitioning of P and assumed that acid-lactate-extractable P represented a labile pool of P in instant equilibrium with soil solution P. Additionally, oxalate-extractable inorganic P was presumed to comprise the sum of the labile and stable pools of P, with mass flux to and from the latter described by Fick’s first law. The model was evaluated using results from extractions and P K-edge XANES spectroscopy. Notably, organic P, as revealed by P K-edge XANES, did not substantially contribute to long-term changes in soil P content and was therefore excluded from consideration. In general, the model offered reasonable fits to the extracted P concentrations. However, for the P-depleted treatments, a prerequisite was that the P removal through harvest was lower compared to measurements. Conversely, in three of the soils, the modelled fertilizer inputs needed to be reduced to 70 % to 85 % of the known additions. These discrepancies may be attributed to the involvement of deeper soil horizons, including deep crop uptake and mixing with lower soil layers, although other factors such as lateral dispersion and inaccuracies in estimating applied fertilizers cannot be discounted. These results underscore the necessity of gaining a more comprehensive understanding of how deeper soil horizons influence P mass balances in agricultural soils. In one of the soils, Fjärdingslöv, P K-edge XANES results demonstrated the formation of calcium phosphate over time in the highest fertilization treatment, consistent with the model. Additionally, in two soils, Kungsängen and the P-depleted Vreta Kloster soil, the model predicted a significant contribution from mineral weathering. However, the PBalD8 model also projected higher P leaching rates than those observed, suggesting that the model may not fully capture this P output term.

Rapeseed Yield in a Maize – Rapeseed Cropping Pattern over a Long-Term Nutrient Management Experiment

A long-term soil fertility experiment in maize (Zea mays) – rapeseed (Brassica campestris var. toria) cropping system was initiated in Nepal Agricultural Research Council (NARC), Directorate of Agricultural Research (DoAR), Lumbini Province, Banke, Khajura (the then Regional Agricultural Research Station) since 1994. The field experiment was designed in the randomized complete block including nutrient as treatment at nine rates (0–0–0 nitrogen – phosphorus – potash (N–P2O5–K2O) kg/ha, 60–0–0 N–P2O5–K2O kg/ha, 60–40–0 N–P2O5–K2O kg/ha, 60–40–20 N–P2O5–K2O kg/ha, 30–20–10 N–P2O5–K2O kg/ha, 30–20–10 N–P2O5–K2O kg/ha + 30 cm stover from previous maize, 60–40–20 N–P2O5–K2O kg/ha + 30 cm stover from previous maize, farmyard manure 10 t/ha and 30–20–10 N–P2O5–K2O kg/ha + farmyard manure 6 t/ha) and was replicated three times. Rapeseed crop yield attributes including days to flowering, plant height, siliqua per plant, 1000 grains weight, seed yield and straw yield and soil fertility parameters including soil pH, soil organic matter content, soil total nitrogen content, soil available phosphorus content and soil available potash content were monitored from 1994 to 2018 growing seasons. There was a significant effect (p < 0.01) of nutrient treatments in the days to flowering, plant height, siliqua per plant, 1000 grains weight, seed yield and straw yield. The highest mean seed yield (445 kg/ha) was obtained from the nutrient application at the rate of 30–20–10 N–P2O5–K2O kg/ha + farmyard manure 6 t/ha during 1994 – 2018. Yield trend analysis revealed nutrient treatment with farmyard manure both FYM 10 t/ha and 30–20–10 N–P2O5–K2O kg/ha + FYM 6 t/ha had significant positive (p < 0.001, R2 > 0.30) trend of rapeseed seed yield with the maximum 1000 kg/ha rapeseed yield in 2018. Soil analysis results after rapeseed harvest in 2018 showed two nutrient treatments including farmyard manure had significant high soil organic matter (SOM > 1%), soil available phosphorus content (P2O5 > 55 kg/ha) and soil available potash content (K2O > 550 kg/ha). In the long-term, integrated nutrient management applying 30–20–10 N–P2O5–K2O kg/ha + FYM 6 t/ha was the optimal nutrient management option for rapeseed production in maize – rapeseed cropping system at Khajura and similar agro-ecological conditions.

Correction to: Soil microbial biomass phosphorus can serve as an index to reflect soil phosphorus fertility

The effect and relative contributions of C and P inputs on soil microbial biomass P (MBP) accumulation were studied in three long-term soil fertility experiments with various soil and climate characteristics at Qiyang, Yangling, and Wulumuqi. The maximum of soil MBP in all three sites was 47.8 mg P kg-1. The MBP accumulated per unit in soil (mg P kg-1 soil) was correlated with a 4.91 mg kg-1 increase in Olsen P. For each unit increase in P surplus (kg P ha-1), manure C (kg C ha-1), and stubble C (kg C ha-1), MBP accumulation increased by 330, 3.7, and 13 units (μg P kg-1 soil), respectively. The soil MBP was positively correlated with crop yield and P uptake, making the soil MBP a useful soil P fertility index. The critical levels of the soil MBP pool were 140 kg ha-1, 57–62 kg ha-1, and 33–35 kg ha-1 in acidic red soil, loessial soil, and grey desert soil, respectively. This is the first report to establish a quantitative index of soil fertility based on the soil MBP pool. Our findings demonstrate that C input is a good driver of soil MBP accumulation. Integration of the soil MBP as an index of soil P fertility into agricultural P management is useful to help manage mineral P fertilizers as part of sustainable agricultural practices.

Soil microbial biomass phosphorus can serve as an index to reflect soil phosphorus fertility

The effect and relative contributions of C and P inputs on soil microbial biomass P (MBP) accumulation were studied in three long-term soil fertility experiments with various soil and climate characteristics at Qiyang, Yangling, and Wulumuqi. The maximum of soil MBP in all three sites was 47.8 mg P kg-1. The MBP accumulated per unit in soil (mg P kg-1 soil) was correlated with a 4.91 mg kg-1 increase in Olsen P. For each unit increase in P surplus (kg P ha-1), manure C (kg C ha-1), and stubble C (kg C ha-1), MBP accumulation increased by 330, 3.7, and 13 units (μg P kg-1 soil), respectively. The soil MBP was positively correlated with crop yield and P uptake, making the soil MBP a useful soil P fertility index. The critical levels of the soil MBP pool were 140 kg ha-1, 57–62 kg ha-1, and 33–35 kg ha-1 in acidic red soil, loessial soil, and grey desert soil, respectively. This is the first report to establish a quantitative index of soil fertility based on the soil MBP pool. Our findings demonstrate that C input is a good driver of soil MBP accumulation. Integration of the soil MBP as an index of soil P fertility into agricultural P management is useful to help manage mineral P fertilizers as part of sustainable agricultural practices.

Soil properties currently limiting crop yields in Swedish agriculture – An analysis of 90 yield survey districts and 10 long-term field experiments

• Among manageable soil properties, soil pH and extractable soil P had the largest impact on Swedish crop yields. • Current recommendations on soil pH and soil P require upward adjustment. • Surprisingly, increasing soil organic matter (SOM) reduced yields, most probably due to lower pH in soils richer in SOM. This study evaluated yield statistics and data from a comprehensive national soil inventory representing 90 yield survey districts and from the Swedish long-term soil fertility experiments. The aim was to identify the most yield-limiting soil properties and best agronomic practices in order to further improve yield. Principal Component Analysis, multi-variate analysis, step-wise regression, and tree partitioning analysis identified the same variables affecting yields in the national and experimental datasets. Crop yields were significantly affected by soil pH, soil organic matter (SOM), plant-available soil phosphorus (P-AL) and mean annual temperature. Contents of plant-available potassium and magnesium in soil had no significant impact on yield, except in potatoes. Soil pH was found to have the greatest potential to affect crop yields, even at values >6.5 (pH (H2O) ). Soil organic matter ranging from 3 to 6% in Swedish arable soils had an indirect negative effect on crop yields by lowering soil pH values with higher SOM content. To fully exploit the known benefits of SOM, liming requires more attention. One important finding was that current Swedish agricultural recommendations require updating. High-yielding crops demand more plant-available soil P and a range of 60−100 mg P-AL kg −1 soil is needed for sufficient P supply. A new target value of pH 7 for all crops except potatoes is recommended.

Weed Dynamics and Yield of Wheat in Long Term Soil Fertility Experiment under Rice-Rice-Wheat Cropping System

Weed dynamics and yield and yield parameters of wheat was studied in long-term soil fertility experiment under rice-rice-wheat system during winter season of 2018-19. The experiment was laid out in randomized complete block design with nine treatments replicated three times. Treatments were applied as: T1- no nutrients added, T2- N added; T3- N and P added; T4- N and K added; T5- N2:P2O5:K2O added at recommended rate for all crops. Similarly, T6- only N added in rice and N2:P2O5:K2O in wheat at recommended rate; T7- half N; T8- half NP of recommended rate for both crops; and T9- farmyard manure @10 t ha-1 for all crops in rotation. The results revealed that the use of Farm Yard Manure @ 10 t ha-1 gave significantly higher yield of 2393 kg ha-1 followed by recommended chemical fertilizer dose of 100:40:30 N:P2O5:K20 kg ha-1 of 2383 kg ha-1. Considerably, lower grain yield was obtained from treatments that did not receive phosphorus. Similarly, application of FYM @10 t ha-1 followed by recommended fertilizer dose recorded higher weed density and dry weed weight with compared to any of N,P2O5 and K2O or all nutrient omitted treatments.

Assessing the ability of soil tests to estimate labile phosphorus in agricultural soils: Evidence from isotopic exchange

Efficient phosphorus (P) fertilization strategies are essential for intensive crop production with minimal negative environmental impacts. A key factor in sustainable P use is assessment of the plant available soil P pool using soil P tests. This study determined isotopically exchangeable P after six days of reaction with 33PO4 (P-E (6 d)) to determine how accurately two commonly used P tests, Olsen and AL (acid ammonium acetate lactate) can quantify the amount of labile P. Soil samples were taken from both highly P-amended and unamended plots at six sites within the Swedish long-term soil fertility experiments. According to P K-edge XANES spectroscopy, the P speciation was dominated by Al-bound P and organic P, with additional contributions from Fe-bound P and Ca phosphates in most soils. The results showed that the AL test overestimated P-E (6 d) by a factor of 1.70 on average. In contrast, the Olsen test underestimated P-E (6 d), with the mean ratios of P-Olsen to P-E (6 d) being 0.52 for high-P and 0.19 for low-P soils. The 33P/31P ratio in the Olsen extract of a 33PO4 spiked soil was closer to that of a 0.005 mol L−1 CaCl2 soil extract than the corresponding ratio in the AL extract, suggesting that AL extraction solubilized more non-labile P. In conclusion, the AL and Olsen methods are not suitable for direct quantification of the isotopically exchangeable soil P pool after 6 days of equilibration. However, based on the results, Olsen may be superior to AL for classification of soil P status, due to its even performance for calcareous and non-calcareous soils and lower extraction of non-labile P.

Chemical fertilizers could be completely replaced by manure to maintain high maize yield and soil organic carbon (SOC) when SOC reaches a threshold in the Northeast China Plain

The combined use of chemical and organic fertilizers is considered a good method to sustain high crop yield and enhance soil organic carbon (SOC), but it is still unclear when and to what extent chemical fertilizers could be replaced by organic fertilizers. We selected a long-term soil fertility experiment in Gongzhuling, Northeast China Plain to examine the temporal dynamics of crop yield and SOC in response to chemical nitrogen, phosphorus, and potassium (NPK) fertilizers and manure, applied both individually and in combination, over the course of three decades (1980–2010). We aimed to test 1) which fertilizer application is the best for increasing both maize yield and SOC in this region, and 2) whether chemical fertilizers can be replaced by manure to maintain high maize yield and enhance SOC, and if so, when this replacement should be implemented. We observed that NPK fertilizers induced a considerable increase in maize yield in the first 12 years after the initiation of the experiment, but manure addition did not. In the following years, the addition of both NPK fertilizers and manure led to an increase in maize yield. SOC increased considerably in treatments with manure but remained the same or even declined with NPK treatments. The increase in maize yield induced by NPK fertilizers alone declined greatly with increasing SOC, whereas the combination of NPK and manure resulted in high maize yield and a remarkable improvement in SOC stock. Based on these results we suggested that NPK fertilizers could be at least partially replaced by manure to sustain high maize yield after SOC stock has reached 41.96 Mg C ha−1 in the Northeast China Plain and highly recommend the combined application of chemical fertilizers and manure (i.e., 60 Mg ha−1).

Wheat Yield Trend and Soil Fertility Status in Long Term Rice-Rice-Wheat Cropping System

A long-term soil fertility experiment under rice-rice-wheat system was performed to evaluate the long term effects of inorganic fertilizer and manure applications on soil properties and grain yield of wheat. The experiment began since 1978 was laid out in randomized complete block design with 9 treatments replicated 3 times. From 1990 onwards, periodic modifications have been made in all the treatments splitting the plots in two equal halves of 4 x 3 m2 leaving one half as original. In the original treatments, recent data revealed that the use of Farm Yard Manure (FYM) @10 t ha-1 gave significantly (P≤0.05) higher yield of 2.3 t ha-1 in wheat, whereas control plot gave the lowest grain yield of 277 kg ha-1. Similarly, in the modified treatments, the use of FYM @10 t ha-1 along with inorganic Nitrogen (N) and Potassium oxide (K2O) @ 50 kg ha-1 produced significantly (P≤0.05) the highest yield of 2.4 t/ha in wheat. The control plot with an indigenous nutrient supply only produced wheat yield of 277 kg ha-1 after 35th year completion of rice-rice-wheat system. A sharp decline in wheat yields was noted in minus N, phosphorus (P), Potassium (K) treatments during recent years. Yields were consistently higher in the N:P2O5:K2O and FYM treatments than in treatments, where one or more nutrients were lacking. The application of P2O5 and K2O caused a partial recovery of yield in P and K deficient plots. There was significant (P≤0.05) effect of use of chemical fertilizers and manure on soil properties. The soil analysis data showed an improvement in soil pH (7.8), soil organic matter (4.1%), total N content (0.16%), available P (503.5 kg P2O5 ha-1) and exchangeable K (137.5 kg K2O ha-1) in FYM applied treatments over all other treatments. The findings showed that the productivity of the wheat can be increased and sustained by improving nutrient through the integrated use of organic and inorganic manures in long term.Journal of Nepal Agricultural Research Council Vol.1 2015 pp.21-28

N2O emissions in a long-term soil fertility experiment under maize–wheat cropping system in Northern India

The agriculture sector is a major contributor towards global N2O (nitrous oxide) emissions. Amongst various factors controlling N2O emissions from cultivated fields, application of fertilizers and manures is the key factor. The effect of 42years of continuous application of inorganic fertilizers and farmyard manure (FYM) on N2O emissions in loamy sand soil was studied via closed chambers and gas chromatography. Daily N2O fluxes from five treatments: 100% NPK (T1), 150% NPK (T2), 100% N (T3), 100% NPK+FYM (T4) and Control (T5), of an onging experiment under maize-wheat cropping system on Typic Ustochrept in Northern India, were measured during maize and wheat crop seasons. The average N2O fluxes in T1, T2, T3, T4 and T5 treatments during maize crop season were 56.2, 60.8, 58.5, 59.2 and 24.6 N2O-Ngha−1day−1, respectively and in the wheat crop season 17.1, 19.7, 17.2, 19.4 and 11.5 N2O-Ngha−1day−1, respectively. Total N2O emissions in long-term fertilizer or manure treatments were approximately 100 and 50% higher than control in the maize and wheat crop seasons, respectively. Various long-term treatments had significant effect on status of various soils C and N forms, which in-turn influenced N2O emissions. Regression analysis revealed that water-input either from rainfall or irrigation controlled nearly 50% of the seasonal variations in N2O fluxes in the control treatment and about 20% variations in fertilizer and manure treatments. This suggested that in addition to irrigation or rainfall, fertilizer application also played an important role in N2O emissions. Although carbon-equivalent emissions were higher from balanced fertilization or FYM application treatments, yield-scaled global warming potentials (GWP) were lower due to higher maize and wheat grain yields in these treatments. Long-term maize-wheat cropping without any nutrient application or imbalanced fertilization resulted in higher yield-scaled GWP. The findings suggested that to achieve food security and curtail N2O emissions, balanced fertilization or integrated nutrient management may be adopted.

Towards an unbiased method for quantifying treatment effects on soil carbon in long-term experiments considering initial within-field variation

Agricultural management effects on soil organic carbon (SOC) can be significant, but are often relatively small compared with the total SOC pool and its field–scale variability. In field experiments, completely uniform initial SOC concentrations across all plots are unlikely. Therefore, measured treatment effects through time are biased by these initial differences. This study questioned how much this bias can represent and whether it can be neglected or must be accounted for. In 1116 investigated pairs of treatments in 10 meta-replicated Swedish long-term soil fertility experiments, the average absolute initial difference in SOC was 1.3g Ckg−1, whereas the average absolute difference after about 50years of contrasting management was 1.5g Ckg−1. Initial differences in SOC were significantly correlated with final differences (R2=0.14) and in 47% of all investigated pairs the absolute initial difference was higher than the absolute final difference. However, simple subtraction of initial differences between pairs from final differences to isolate the treatment effect neglect the fact that the soil with the higher initial SOC content will lose proportionally more C through mineralization during the experimental period higher SOC content caused higher SOC mineralisation during the experimental period. Therefore, a first-order kinetic model was used to predict the decrease in initial SOC differences over time as influenced by climate. We derived a generic empirical equation that can be used to account for this severe but inherent problem with plot experiments. According to the equation, 65 and 69% of the initial differences in SOC between treatment pairs persisted after 50years under the climate conditions in southern and central Sweden, respectively. We conclude that initial differences can be severe and have to be accounted for. The proposed empirical equation can reduce the bias in treatment comparisons for different climatic conditions and contribute to improve the quality of data interpretation from long-term field experiments.

Properties of soils in the Swedish long-term fertility experiments: VII. Changes in topsoil and upper subsoil at Örja and Fors after 50 years of nitrogen fertilization and manure application

We tested the hypothesis whether fertilization has an impact on subsoil development using data from two long-term soil fertility experiments. We chose treatments without nitrogen (N) and high N fertilizer addition in two crop rotations with and without ley and farmyard manure application. The soil properties measured included soil organic matter, microbial composition, aggregate stability, readily dispersible clay and micronutrient content in topsoil (0–30 cm) and upper subsoil (30–40 cm). Studies of two adjacent soil profiles revealed that the upper subsoil of an N-fertilized treatment had more soil organic matter, darker colour, more aggregation, more fine roots and was 10 cm thicker than that of the no-N treatment. This pronounced subsoil development in treatments with higher yields (high N input) was corroborated by carbon mass determinations based on systematic sampling including bulk density. Soil organic matter contents were higher in N-fertilized than unfertilized treatments, either with or without manure. Nitrogen fertilization caused distinct differences in microbial composition at one study site. Phospholipid fatty acid analysis revealed: (1) that mineral N fertilizer promoted nitrifiers; and (2) that bacteria were favoured over fungi in treatments with N supply probably due to nitrogen-rich crop residues. Soil aggregate stability (water dispersion) was correlated to soil organic matter and clay content. We also tested the hypothesis whether trace element contents in the top- and subsoil were affected by N fertilization through removal by large yields. Despite long-term depletion, crop removal of micronutrients was too small to cause significant differences in soil between treatments.

Effect of Nitrogen Fertilizer Rate and Harvest Season on Forage Yield, Quality, and Macronutrient Concentrations in Midland Bermuda Grass

Bermuda grass [Cynodon dactylon (L.) Pers.] is a major forage for grazing and hay production in the southern United States. The objectives of this study were to determine effects of nitrogen (N) fertilization rate (0, 112, 224, 336, and 448 kg ha−1), split spring and summer applications of N at the 224 and 448 kg ha−1 rates, and harvest periods (spring and summer) on forage yield, crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), total digestible nutrients (TDN), and concentrations of phosphorus (P), potassium (K), magnesium (Mg), and calcium (Ca in Midland Bermuda grass. Data were collected from 2002 to 2008 as part of an ongoing, long-term soil fertility experiment in southern Oklahoma. Repeated measures analysis of these long-term data showed that forage yield responses to N rate varied with year and harvest time with up to 2.5-fold yield differences among years. Nitrogen fertilization increased CP, TDN, and macronutrient P and Mg and decreased ADF and NDF. Crude protein was increased by ≥50%, and ADF and NDF dropped by up to 25% with the greatest N rate. In general, split N applications did not affect forage yield but produced low-quality forage compared to single N application in spring. Split application of 448 kg N ha−1 gave forage with CP, TDN, ADF, and NDF similar to the Bermuda grass receiving 336 or 448 kg N ha−1 as a single application. Spring forage had better forage quality than summer harvests. While N fertilization increased forage Mg and P concentrations by more than 50% during both spring and summer, it had no effect or slight increased K and Ca concentrations. In the southern Great Plains, despite the weather-dependent variability in forage yield of Bermuda grass, N application increase forage quality.

Properties of soils from the Swedish long-term fertility experiments: VI. Mapping soil electrical conductivity with different geophysical methods

Swedish long-term soil fertility experiments were used to investigate the effect of texture and fertilization regime on soil electrical conductivity. In one geophysical approach, fields were mapped to characterize the horizontal variability in apparent electrical conductivity down to 1.5 m soil depth using an electromagnetic induction meter (EM38 device). The data obtained were geo-referenced by dGPS. The other approach consisted of measuring the vertical variability in electrical conductivity along transects using a multi-electrode apparatus for electrical resistivity tomography (GeoTom RES/IP device) down to 2 m depth. Geophysical field work was complemented by soil analyses. The results showed that despite 40 years of different fertilization regimes, treatments had no significant effects on the apparent electrical conductivity. Instead, the comparison of sites revealed high and low conductivity soils, with gradual differences explained by soil texture. A significant, linear relationship found between apparent electrical conductivity and soil clay content explained 80% of the variability measured. In terms of soil depth, both low and high electrical conductivity values were measured. Abrupt changes in electrical conductivity within a field revealed the presence of ‘deviating areas’. Higher values corresponded well with layers with a high clay content, while local inclusions of coarse-textured materials caused a high variability in conductivity in some fields. The geophysical methods tested provided useful information on the variability in soil texture at the experimental sites. The use of spatial EC variability as a co-variable in statistical analysis could be a complementary tool in the evaluation of experimental results.

Soil organic carbon and nitrogen stocks in Nepal long-term soil fertility experiments

Loss of organic C from tilled agricultural soils has generated interest in C-sequestration in soils. The effects of nutrient and organic inputs on soil organic carbon (SOC) and total nitrogen (TN) stocks were studied in three 23–25-year-old long-term conventional tillage fertility experiments (LTFEs) in the Nepal terai. The sites differed in soil texture and were cropped annually to rice (Oryza sativa L.) and wheat (Triticum aestivum L.). Treatments were control (unfertilized), recommended NPK, and farmyard manure (FYM; 4 Mg dry wt./crop) at all sites, plus FYM (4 Mg ha−1 year−1) or chopped wheat straw (8 Mg dry wt. ha−1 year−1) plus N to rice and NPK to wheat at Parwanipur. Small areas of unfertilized grassland created at the same time as the LTFEs were sampled to provide a no-tillage comparison. Soil samples were collected at 15 cm intervals to a depth of 60 cm.

Trace element concentration in wheat grain: results from the Swedish long-term soil fertility experiments and national monitoring program

Concentrations of trace elements in wheat grain sampled between 1967 and 2003 from the Swedish long-term soil fertility experiments were analyzed using ICP-MS. The long-term effect of inorganic and organic fertilization on trace metal concentrations was investigated including the impact of atmospheric deposition and myccorhiza, whereas other factors such as soil conditions, crop cultivar, etc. are not discussed in this paper. Mean values derived from 10 experimental sites were reported. Significantly declining Pb and Cd concentrations in wheat grain could be explained by lower atmospheric deposition. Mean Se contents in all samples were 0.031 mg kg(-1) grain dry weight. No samples had sufficiently high Se concentrations for human (0.05 mg Se kg(-1)) or animal demand (0.1 mg Se kg(-1)). Concentrations of Co in wheat grain were extremely low, 0.002-0.005 mg Co kg(-1) grain dry weight, and far below the minimum levels required by animals, which applied to all fertilizer treatments. A doubling of Mo concentrations in grain since 1975 resulted in Cu/Mo ratios often below one, which may cause molybdenosis in ruminants. The increase in Mo concentrations in crops correlated with the decline in sulfur deposition. Concentrations of Cu and Fe declined in NPK-fertilized wheat as compared to unfertilized or manure-treated wheat. Very low concentrations of Se and Co and low concentrations of Fe and Cu require attention to counteract risks for deficiencies. The main characteristic of the study is that there are few significant changes over time between different fertilizer treatments, but throughout there are low concentrations of most trace elements in all treatments. In general, good agreement between concentrations in wheat from the long-term fertility experiments and the national monitoring program indicate that values are representative.

Dynamics of Soil Microbial Biomass Carbon, Mineral Nitrogen and Nitrogen Mineralization in Long-Term Field Experiment, Northern China

ABSTRACT A long-term field soil fertility and crop yield experiment was carried out at China Agricultural University's Qu-Zhou experiment station in Hebei Province, Northern China. The station is in a continental temperate monsoon tone, and the climate in the region is warm, sub-humid, and consists of summer rainfall and dry-cold winters. The soil at study site is an improved silt fluvo-aquic soil. Three different farming systems were established in 1993: traditional compost (TC), chemical fertilizer (CF), and a control (CK). Soil samples were collected in October 2004 before the fertilizer application, during the crop growing stage (November 2004; March, April, May 2005) and at harvest (June 2005). The soil microbial biomass carbon (MBC), mineral nitrogen concentration, and nitrogen mineralization rate were evaluated. The results showed that soil MBC, mineral nitrogen concentration, and nitrogen mineralization rate were higher in TC and CF than in CK. The microbial biomass C in TC were significantly higher compared with CF and CK; although only slightly higher in CF compared with CK. Mineral nitrogen (NH4-N and NO3-N) concentration on 14 October 2004 and 25 May and 10 June 2005 among treatments followed the order: CK < CF < TC. Nevertheless, the order in November 2004 and March, April, and 10 May 2005 among treatments followed: CK < TC < CF. NH4-N concentration was always lower than NO3-N concentration. Significant differences in the nitrogen mineralization rate were observed between treatments and incubation dates. Nitrogen mineralization rate among treatments followed the order: CK < CF < TC. Nitrogen mineralization rate was positively correlated with microbial biomass carbon and wheat yield. Microbial biomass carbon was a good indicator for changes of soil fertility and quality.

Modeling Soil Organic Matter Dynamics Under Intensive Cropping Systems on the Huang-Huai-Hai Plain of China

ABSTRACT A modified CQESTR model, a simple yet useful model frequently used for estimating carbon sequestration in agricultural soils, was developed and applied to evaluate the effects of intensive cropping on soil organic matter (SOM) dynamics and mineralization as well as to estimate carbon dioxide emission from agricultural soils at seven sites on the Huang-Huai-Hai Plain of China. The model was modified using site-specific parameters from short- and mid-term buried organic material experiments at four stages of biomass decomposition. The predicted SOM results were validated using independent data from seven long-term (10- to 20-year) soil fertility experiments in this region. Regression analysis on 1151 pairs of predicted and measured SOM data had an r2 of 0.91 (P ≤ 0.01). Therefore, the modified model was able to predict the mineralization of crop residues, organic amendments, and native SOM. Linear regression also showed that SOM mineralization rate (MR) in the plow layer increased by 0.22% when annual crop yield increased by 1 t ha−1 (P ≤ 0.01), suggesting an improvement in SOM quality. Apparently, not only did the annual soil respiration efflux merely reflect the intensity of soil organism and plant metabolism, but also the SOM MR in the plow layer. These results suggested that the modified model was simple yet valuable in predicting SOM trends at a single agricultural field and could be a powerful tool for estimating C-storage potential and reconstructing C storage on the Huang-Huai-Hai Plain of China.

Indirect Estimates of Soil Electrical Conductivity for Improved Prediction of Wheat Grain Yield

A system of midseason prediction of winter wheat grain yield based on sensed plant growth properties has been established. However, little research has been conducted to determine the relationship of grain yield, sensed plant data, and soil electrical conductivity (EC). This study was carried out to determine if soil EC could be useful in better predicting wheat grain yield. During 2001 and 2002, measurements of soil EC, normalized difference vegetative index (NDVI), and grain yield were taken on five long-term soil fertility experiments across Oklahoma. Results indicated that soil EC was not better than mid-season NDVI readings at predicting grain yield at any location or year. A combination of soil EC and NDVI was also less correlated with grain yield than NDVI alone. This study showed that pseudostatic soil EC measurements did not improve upon the in-season prediction of winter wheat grain yields that could be successfully accomplished by using NDVI alone.

Indirect Estimates of Soil Electrical Conductivity for Improved Prediction of Wheat Grain Yield

A system of midseason prediction of winter wheat grain yield based on sensed plant growth properties has been established. However, little research has been conducted to determine the relationship of grain yield, sensed plant data, and soil electrical conductivity (EC). This study was carried out to determine if soil EC could be useful in better predicting wheat grain yield. During 2001 and 2002, measurements of soil EC, normalized difference vegetative index (NDVI), and grain yield were taken on five long-term soil fertility experiments across Oklahoma. Results indicated that soil EC was not better than mid-season NDVI readings at predicting grain yield at any location or year. A combination of soil EC and NDVI was also less correlated with grain yield than NDVI alone. This study showed that pseudostatic soil EC measurements did not improve upon the in-season prediction of winter wheat grain yields that could be successfully accomplished by using NDVI alone.