Long-term Crop Rotation Effects Research Articles

Long-term effects of crop rotation and nitrogen fertilization on phosphorus cycling and balances in loess-derived Mollisols

Developing meaningful agroecosystem soil P inventories necessitates moving beyond single measures of readily extractable inorganic P (Pi) limited to surface depths. We drew on a long-term (36 year) experimental field trial in the US Maize Belt (northwestern Illinois) to evaluate how crop rotation [maize-maize (Zea mays L.) vs maize-soybean (Glycine max L. Merr.)] and N fertilization (0 vs 269 kg N ha−1) impact P dynamics throughout the soil profile by using sequential fractionation and phosphatase activity assays, contextualized by soil P stocks and agronomic P balances. Distribution of P fractions by depth (0–15, 15–30, 30–60, 60–90 cm) indicate that management effects were limited to the surface soil layers (0–30 cm). Soil P fractions differed more by depth than by experimental treatments. Long-term N fertilization significantly decreased pH concurrently with labile organic P (Po) and phosphodiesterase activity. Soil labile inorganic P (Pi) was two-fold lower under N fertilization compared to zero N fertilization, reflecting greater yield and thus P export via grain harvest. Under N fertilization, integration of soybean elevated soil phosphodiesterase activity and decreased water-extractable Po. Higher stocks of soil Po than labile Pi at surface depths (0–30 cm) corroborated a hypothesized appreciable pool size of soil Po relative to the labile Pi pool to which most agronomic assessments are limited. Large negative agronomic balances over the 36-year period (−426 to −945 kg P ha−1) are suggestive of legacy P from pre-experiment manure application and high native P stocks, with net P export equivalent to 11–35% of soil P stocks at 0–90 cm depth at the initiation of the experiment. These results contribute to a better understanding how N fertilization and rotation practices influence soil P cycling and stocks, thereby informing P budgets for comprehensive agroecosystem P management.

The Effect of Monoculture, Crop Rotation Combinations, and Continuous Bare Fallow on Soil CO2 Emissions, Earthworms, and Productivity of Winter Rye after a 50-Year Period.

One of the main goals of the 21st century’s developing society is to produce the necessary amount of food while protecting the environment. Globally, particularly in Lithuania and other northern regions with similar climatic and soil conditions, there is a lack of data on the long-term effects of crop rotation under the current conditions of intensive farming and climate change. It has long been recognized that monocultures cause soil degradation compared to crop rotation. Research hypothesis: the long-term implementation of crop rotation makes a positive influence on the soil environment. The aim of our investigation was to compare the effects of a 50-year-long application of different crop rotations and monocultures on soil CO2 emissions, earthworms, and productivity of winter rye. Long-term stationary field experiments were established in 1966 at Vytautas Magnus University Experimental Station (54°53′ N, 23°50′ E). The study was conducted using intensive field rotation with row crops, green manure crop rotations, three-course rotation, and rye monoculture. Pre-crop had the largest impact on soil CO2 emissions, and more intensive soil CO2 emissions occurred at the beginning of winter rye growing season. Rye appeared not to be demanding in terms of pre-crops. However, its productivity decreased when grown in monoculture, and the optimal mineral fertilization remained lower than with crop rotation, but productivity remained stable.

Long-term effects of crop rotation, tillage, and fertilizer nitrogen on soil health indicators and crop productivity in a temperate climate

Although diversifying crop rotations with perennials and cover crops and implementing no-tillage practices has been promoted as an effective strategy for increasing soil carbon and nitrogen storage in the long-term, uncertainty still remains, particularly regarding the association between crop productivity and soil health. Therefore, using two long-term experiments, we investigated the effects of crop rotation, tillage system, and nitrogen fertilizer application (at Ridgetown only) on surface soil (0−15 cm depth) parameters (soil organic carbon (SOC), total nitrogen (TN), commercial soil health tests (evolved CO2 and NH3 indicating microbial activity)), and crop yield in 2016. We used 5-yr average crop yield variability to test for the relationship of SOC and TN with crop yield stability. Results indicated that diversification of corn and soybean rotations and their monocultures with cover crops, perennials, and small grain cereals enhanced soil health indicators (by 32% at Ridgetown (21 yr) and 49% at Elora (36 yr)) and crop productivity (16% at Ridgetown and 29% at Elora). At Ridgetown, corn yield was 10.4% greater with including red clover to the corn-soybean-winter wheat than monoculture corn. Similarly, corn yield was enhanced by 25% when alfalfa was added to monoculture corn at Elora. Nitrogen fertilizer application did not increase surface SOC storage at Ridgetown. No-tillage system had greater evolved NH3-N (by 7.2%) and evolved CO2-C (by 27.9%) than conventional tillage at Elora only. Consistent with management effects on crop yield, at both sites, evolved NH3-N and CO2-C were greatest from rotations with winter wheat, red clover, and alfalfa. Additionally, a strong positive relationship of SOC and TN with soil health tests confirms the suitability of the commercial tests to detect management effects on soil health indicators in the long-term. At both sites, SOC positively correlated with crop yield indicating a direct association between soil carbon status and agroecosystem resiliency. We conclude that diversifying crop rotations increases soil microbial activity, surface SOC sequestration, and crop productivity in the long-term; thus, is a critical component for developing sustainable agroecosystems.

Effect of rice-rice-rape rotation on physicochemical property and bacterial community of rhizosphere soil

Through collecting rhizosphere soil sample from a 30-year long-term fixed location test site that use “rice-rice-rape” crop rotation (RRR) and “rice-rice-fallow” continuous cropping systems (RRF), this paper investigated effects of long-term crop rotation on physicochemical property and bacterial community of rhizosphere soil. Results showed that total nitrogen (TN), total phosphorus (TP) and available potassium (AK) contents in rhizosphere soil under long-term RRR were decreased by 28.09%, 15.69% and 6.25% respectively. Alkali-hydrolyzable nitrogen (AN) and available phosphorus (AP) contents were 10.59% and 13.25% higher than those of soil in RRF respectively. Three soil samples collected during different periods also showed that RRR resulted in a lower rhizosphere soil pH than RRF. Clone library analysis revealed that significant difference in rhizosphere soil bacterial community was observed between RRR and RRF continuous cropping. Abundance of α-Proteobacteria, β-Proteobacteria and γ-Proteobacteria were higher in rhizosphere soil of RRR compared to RRF. pH of rhizosphere soil was significantly correlated with Acidobacteria level, while total organic carbon (TOC) content was significantly correlated with Proteobacteria level. Long-term RRR enhanced conversion of N and P in rhizosphere soil, increased bio-availability to crop, and promoted diversity of soil bacterial community. Bacterial diversity in RRR could be ecological significance in maintaining soil fertility and functionality.

Long-term crop rotation effects on winter and spring cereals productivity

A long-term field experiment was carried out at the Experimental Station of the VDU Agriculture Academy (formerly Aleksandras Stulginskis University), Institute of Agroecosystems crop rotation collection (equipped in 1967), during 2015–2017. The soil of the Experimental site is moderately fine textured Calc(ar)i-Endohypogleyic Luvisol. The research was carried out on winter rye (Secale cereale L.) ‘Matador’, winter wheat (Triticum aestivum L.) ‘Skagen’ and 71 spring barley (Hordeum vulgare L.) ‘Orphelija’, which were sown in 8 different crop rotations after different preceding crops and rye monoculture. The aim of the experiment was to investigate the effect of long-term crop rotation combinations on testing crops yield and productivity indicators. In many cases, rye productivity indicators were lower during 50-year monocropping. The best productivity indicators were obtained by growing rye in them in grass and fallow crop sequences, and for winter wheat in fallow with vetch–oat mixture for fodder and after manure application. In rye these indicators were more dependent on the precipitation amount and the amount of the sum of temperature during the period of generative organ formation. Among these indicators and the number of productive stems, a statistically strong and medium strength correlation interaction was identified: r = 0.83, P ≤ 0.01; r = 0.90, P ≤ 0.05; r = 0.58, P ≤ 0.05; r = 0.85, P ≤ 0.01; and winter weat r = 0.87, P ≤ 0.01; r = 0.89, P ≤ 0.01. The highest winter wheat productivity was established in crop rotation after perennial grasses and leguminous crops. Crop yield in monoculture decreases, but the optimal amount of mineral fertilizers saves lower but stable yields. Spring barley is less dependent on preceding crop, so it can be grown after winter cereals. However, they are more productive when sown after row crops and in crop rotations where one of the rotation members is fertilized with organic fertilizers.

Soil fertility and phosphorus fractions in a calcareous chernozem after a long-term field experiment

In the present study, the long-term effects of crop rotation and fertiliser (manure, harvest residues and mineral fertilisers) use on the presence of phosphorus and its fractions at different soil depths was monitored and analysed in relation to the long-term use of particular maize growing systems. The 270 analysed soil samples were obtained as a part of a long-term two-factorial trial with four replications initiated in 1965. The plan of divided plots (split-plot design with randomised variants) was adopted and the following factors were analysed: (1) Fertilising systems: single-crop system (control, NPK, NPK + maize remains, NPK + manure) and two-crop rotation – maize / barley (NPK + manure) and (2) Soil layers at different depths: 0–20 cm, 20–40 cm, and 40–60 cm. The highest value of readily available phosphorus was found in all studied soil layers in the two-crop rotation treatment with organic and mineral fertilisers. On the other hand, the treatments involving manure application resulted in the highest content of total and organic phosphorus, whereby a 27–70% increase was observed, depending of the variant. The greatest presence of Ca-P fraction was obtained in treatments based on organic matter use, ranging from 364.4 to 482.8 mg kg−1. Nonetheless, in the treatments involving application of organic matter, fraction related to this group had a significantly lower contribution to the total inorganic phosphorus, ranging from 56% to 86%, depending on the variant. Correlations obtained via principal component analysis (PCA) showed clear demarcation among treatments and control samples based on the use of manure and mineral fertilisers.

Long-term effects of crop rotation, manure and mineral fertilisation on carbon sequestration and soil fertility

Abstract Carbon sequestration, recently advocated to mitigate climate change, needs a thorough knowledge of the dynamics of soil organic carbon (SOC), whose study requires long-term experiments. A field trial started in 1967 is still in progress in the Southeast Po valley (Italy). It compares a 9-year rotation (corn–wheat–corn–wheat–corn–wheat–alfalfa–alfalfa–alfalfa), two 2-year successions (corn–wheat and sugarbeet–wheat), continuous corn and continuous wheat. During the first 18 years (up to 1984) wheat crops were always followed by catch crops of silage corn. Within each rotation, three rates of cattle manure have been factorially combined with three mineral NP rates. In 1984 the highest manure application was stopped. Wheat straw and corn stalks have always been removed from the field. Since 1972 up to now every year we have determined the organic C and total N contents in soil samples collected from 0.40-m depth. During the first 18 years (in the presence of the catch crop) SOC exponentially declined, probably as a consequence of the intensification of tillage depth and crop succession with respect to the previous conventional agriculture. The intensification regarded ploughing, which became deeper, the number of cropped species that in most treatments was reduced, and mineral N application, which, on average, increased. The drop was faster in the sugarbeet–wheat succession than in the 9-yr rotation and continuous wheat. After 1985, without the catch crop, SOC linearly increased, faster in the 9-yr rotation and continuous wheat than in sugarbeet–wheat. The results can be ascribed to the amount and C/N ratio of debris remaining in the field after each crop, even after having taken away wheat straw and corn stalks. The debris consisted of sugarbeet tops, with a low C/N ratio, and of roots and basal culms of the two cereal crops with higher C/N ratio. Mineral fertilizers significantly increased SOC, probably for the greater amount of cereal roots and sugarbeet tops in more fertilized plots. The influence of manure was less intense, but its benefits lasted longer than 18 years after its interruption. Soil N content was more related to accumulated organic matter than to mineral N fertilisation. In conclusion the highest C sequestration was obtained with manure addition, with the highest rate of mineral fertilizers, and in the rotation containing the alfalfa ley. The effects of these factors were not additive.

Maize grain and silage yield and yield stability in a long-term cropping system experiment in Northern Italy

This study assesses maize yield and yield stability over a 26-year period in several cropping systems that are part of a long-term crop rotation and agronomic input experiment established in 1985 in Lodi, Lowland of Lombardy, Po Valley, Northern Italy. This experiment compares five fodder crop rotations, specifically: (i) an annually repeated double crop (R1) of autumn-sown Italian ryegrass+spring-sown maize, both used for silage; (ii) a three-year rotation (R3): grain maize (first year) – autumn-sown barley (Hordeum vulgare L.)+spring-sown maize, both for silage (second year) – Italian ryegrass+maize, both for silage (third year); (iii) a six-year rotation (R6): Italian ryegrass+silage maize, both for silage (years 1, 2 and 3 of rotation) – a mixed meadow of white clover (Trifolium repens L.) and tall fescue (Festuca arundinacea Schreb) for hay making (years 4, 5 and 6 of rotation); (iv) a continuous grain maize (CM); and (v) a permanent meadow, established at the beginning of the experiment. All phases of the rotations were carried out every year. Each crop rotation received two levels of agronomic inputs consisting in synthetic and manure fertilization and herbicide rate, corresponding to high (A) and low (B). Treatment A represented a snapshot of agronomic inputs (synthetic fertilizers N–P–K, manure and herbicide amounts) normally applied by the farmers in the region in 1985, when the experiment was undertaken, while treatment B consisted in a 30% reduction of synthetic and manure fertilizers and a 25% reduction of herbicide rate compared to treatment A. The primary objective of this study was to evaluate the long-term effects of crop rotations and the reduction of inputs on maize yield and yield variability. The following conclusions can be drawn: firstly, over 26 years, the yield of grain maize in rotation increased steadily whilst the yield of continuous maize decreased slightly; secondly, a 30% reduction of agronomic inputs decreased the average yield less than proportionally for both grain and silage maize; thirdly, within a given crop rotation, grain and silage maize yields are more stable with higher inputs; and finally, yield stability of grain and silage maize increases with longer rotations. Therefore, management options oriented at increasing cropping system biodiversity have important implications on reducing the temporal variability on maize yield.

Long-term effects of crop rotations and fertilization on soil C and N in a thin Black Chernozem in southeastern Saskatchewan

Lemke, R. L., VandenBygaart, A. J., Campbell, C. A., Lafond, G. P., McConkey, B. G. and Grant, B. 2012. Long-term effects of crop rotations and fertilization on soil C and N in a thin Black Chernozem in southeastern Saskatchewan. Can. J. Soil Sci. 92: 449–461. Carbon sequestration in soil is important due to its influence on soil fertility and its impact on the greenhouse gas (GHG) phenomenon. Carbon sequestration is influenced by agronomic factors, but to what extent is still being studied. Long-term agronomic studies provide one of the best means of making such assessments. In this paper we discuss and quantify the effect of cropping frequency, fertilization, legume green manure (LGM) and hay crops in rotations, and tillage on soil organic carbon (SOC) changes in a thin Black Chernozemic fine-textured soil in southeastern Saskatchewan. This was based on a 50-yr (1958–2007) crop rotation experiment which was initiated on land that had previously been in fallow-wheat (Triticum aestivum L.) (F-W), or F-W-W receiving minimum fertilizer for the previous 50 yr. We sampled soil in 1987, 1996 (6 yr after changing from conventional tillage to no-tillage management and increasing N rates markedly) and again in 2007. The SOC (0–15 cm depth) in unfertilized F-W and F-W-W appears not to have changed from the assumed starting level, even after 20 yr of no-till, but SOC in unfertilized continuous wheat (Cont W) increased slightly [not significant (P>0.05)] in 30 yr, but increased more after 20 yr of no-till (but still not significant). No-till plus proper fertilization for 20 yr increased the SOC of F-W, F-W-W and Cont W in direct proportion to cropping frequency. The SOC in the LGM-W-W (unfertilized) system was higher than unfertilized F-W-W in 1987, but 20 yr of no-tillage had no effect, likely because grain yields and C inputs were depressed by inadequate available P. Soil organic carbon in the two aggrading systems [Cont W (N+P) and F-W-W-hay(H)-H-H (unfertilized)] increased significantly (P<0.05) in the first 30 yr; however, a further 20 yr of no-tillage (and increased N in the case of the Cont W) did not increase SOC suggesting that the SOC had reached a steady-state for this soil and management system. The Campbell model effectively simulated SOC changes except for Cont W(N+P), which it overestimated because the model is ineffective in simulating SOC in very fertile systems. After 50 yr, efficiency of conversion of residue C inputs to SOC was negligible for unfertilized F-W and F-W-W, was 3 to 4% for fertilized fallow-containing systems, was about 6 or 7% for Cont W, and about 11% for the unfertilized F-W-W-H-H-H systems.

Long-term effects of crop rotations and fertilization on soil C and N in a thin Black Chernozem in southeastern Saskatchewan

Lemke, R. L., VandenBygaart, A. J., Campbell, C. A., Lafond, G. P., McConkey, B. G. and Grant, B. 2012. Long-term effects of crop rotations and fertilization on soil C and N in a thin Black Chernozem in southeastern Saskatchewan. Can. J. Soil Sci. 92: 449-461. Carbon sequestration in soil is important due to its influence on soil fertility and its impact on the greenhouse gas (GHG) phenomenon. Carbon sequestration is influenced by agronomic factors, but to what extent is still being studied. Long-term agronomic studies provide one of the best means of making such assessments. In this paper we discuss and quantify the effect of cropping frequency, fertilization, legume green manure (LGM) and hay crops in rotations, and tillage on soil organic carbon (SOC) changes in a thin Black Chernozemic fine-textured soil in southeastern Saskatchewan. This was based on a 50-yr (1958-2007) crop rotation experiment which was initiated on land that had previously been in fallow-wheat (Triticum aestivum L.) (F-W), or F-W-W...

Influences from Long-Term Crop Rotation, Soil Tillage, and Fertility on the Severity of Rice Grain Smuts.

False smut (Ustilaginoidea virens) and kernel smut (Neovossia horrida) are diseases of rice (Oryza sativa) that reduce both grain yield and quality. Susceptible rice cultivars are in widespread use on production acreage in the United States, and the effects from crop management practices on smut control are poorly understood. We studied the long-term effects of crop rotation, soil tillage, and fertility level on rice smut severity. The highest levels of false smut observed in this study were on cultivars grown in rotation with soybean, on traditionally tilled soils, with high fertilizer treatments. The highest levels of kernel smut were observed in a rice-soybean rotation with winter wheat grown between summer crops. These rotations are commonly used in rice-growing regions of the southern United States. Using combinations of crop rotation, soil tillage, and fertility rate, several alternative crop-management practices were identified that provided effective control of smuts in susceptible rice cultivars. The most effective method for controlling both false smut and kernel smut was in 3-year rotations of rice, soybean, and corn. Regardless of rotation order or tillage and fertility treatments within the rotations, rotating out of rice for 2 years was the most effective approach for smut control.

Long-term effects of crop rotation and fertilizers on weed community in spring barley

Integrated weed management programs require a clear understanding of the mechanisms influencing the establishment, growth, and reproduction of unwanted plants (weeds) in agro-ecosystems. This study evaluates the effect of long-term (95 years after the establishment of the site) crop rotation and chemical fertilizers on the weed community dynamics in spring barley at the Agricultural University of Timiriazev, Agricultural Site in Moscow. The weed community occurring on plots of spring barley (grown in crop rotation or continuous) was examined under nitrogen, potassium, phosphorus, NPK, and a control with no fertilizer treatments. Statistical analyses were conducted using analysis of variance (ANOVA) and principal component analysis (PCA). The results show that a) at the study sites, spring weeds are dominant components on agro-ecosystems; b) weed density, particularly of perennials, has significantly decreased under crop rotation; c) the combination of fertilizers (NPK) also decreased the weed density, d) weed density under separate N, P, and K applications was almost the same as that in the control plots. These results suggest that long-term crop rotation and NPK application can strongly affect and reduce weed density in spring barley.

Long-term effects of crop rotations with and without perennial leys on soil carbon stocks and grain yields of winter wheat

A change from cultivated land to grassland generally increases soil organic matter (SOM) content and is a potential option to mitigate greenhouse gas emissions. We investigated the effects of two-year perennial grass and mixed grass/legume leys in a six-year crop rotation on topsoil (0–0.25 m depth) carbon content and on grain yields of winter wheat over a period of 31 years. Different nitrogen fertilisation regimes were included and no manure was added to the experimental plots. We used data from long-term crop rotation experiments at three sites in southern Sweden: Saby (59°49′ N/17°42′ E), Lanna (58°20′ N/13°07′ E) and Stenstugu (57°36′ N/18°26′ E). At Saby, the reduction in topsoil carbon content was smaller in the ley crop rotations than in the crop rotation with only annual crops. There were no statistically significant effects of crop rotation on topsoil carbon at the other two sites. At Lanna, the grain yield increase in winter wheat over time was higher in the mixed legume/grass ley crop rotation than in the other two rotations. Together, these effects of ley on topsoil carbon and winter wheat yield suggest that replacing annual crops with leys in the crop rotation could reduce losses of soil carbon without decreasing total yield of annual crops on a regional scale. We also applied the Introductory Carbon Balance Model (ICBM) to simulate topsoil carbon content at the three sites. Based on the results, measures to improve the model predictability are proposed.

Community structure and functional diversity of indigenous fluorescent Pseudomonas of long-term swine compost applied maize rhizosphere

The community structure and catabolic functional diversity of indigenous rhizosphere fluorescent pseudomonad isolates recovered from un-amended soil (control treated) and following long-term (6 years) swine compost application (compost treated) were studied. Soils collected for the pot experiments were from a Taiwanese experimental farm established in 1995 to study the long-term effects of crop rotation and organic amendment. In the pot experiments, corn seed was cultured; after the elongation stage, 13 and 32 indigenous rhizosphere fluorescent pseudomonad isolates were collected from compost-treated ( n=13) and control-treated ( n=32) soils. All isolates were classified by 16S rDNA restriction fragment length polymorphism (RFLP) and unweighted pair-group method using arithmetic averages analyses. Most (84.4%) of the control-treated soil isolates belonged to genotype A, which corresponded to Pseudomonas putida based on 16S rDNA sequences analysis. However, only 61.5% of compost-treated soil isolates were from genotype A; 30.7% of the isolates belonged to genotype B, whose 16S rDNA profile corresponded to Stenotrophomonas maltophilia. Differing catabolic potentials of the P. putida isolates from control- and compost-treated soils were evident; isolates from control-treated soils utilized organic acids including citric acid, cis-aconitic acid, and formic acid more actively than compost-treated soil isolates. Moreover, the latter isolates more efficiently utilized carbohydrates of i-erythritol and l-rhamnose than P. putida isolates from control-treated soil, consistent with the alteration in the catabolic functions of indigenous rhizosphere P. putida by long-term compost application.

Long-term effects of crop rotation, stubble management and tillage on soil phosphorus dynamics

The effects of various management practices on soil phosphorus (P) dynamics were investigated in a field experiment in New South Wales, Australia, during 24 years of different crop rotation, stubble management, and tillage treatments. Topsoil samples collected at the beginning of the trial and after 6, 12, 18, and 24 years were analysed for resin-extractable P, inorganic and organic P, and total P. According to the calculated P input–output budget, 9–14 of the 20 kg P/ha added as superphosphate annually remained in the system, depending on the treatment. The measured increase in total P in 0–0.20 m did not differ between treatments, showing an accumulation rate of only 9 ± 2 kg P/ha.year. These results suggest a loss of 4 ± 2 kg P/ha.year, presumably into lower soil layers. Resin-extractable P at 0–0.10 m increased by 1.7 kg P/ha.year, irrespective of the treatment. The increase in total P after 24 years was almost completely accounted for by the increase in total extractable inorganic P. Changes in organic P paralleled changes in organic carbon, with a significant loss in treatments with stubble burning (wheat–lupin rotation and continuous wheat), and a significant accumulation in a wheat–subterranean clover rotation with stubble retention and direct drilling. We conclude that on the time scale of this experiment, the dynamics of carbon and organic P are closely linked.

Long-term effects of crop rotation and different fertilization systems on soil fertility and productivity

The effects of crop rotation and fertilization systems on yield and soil fertility parameters have been investigated in a long-term field trial established in southeast Norway in 1953. The results indicate the small differences between crop rotations and different fertilization systems in yield and soil fertility parameters; the decreasing trend in soil organic carbon (SOC) (from 3.8 to 3.7%) and increasing trend of N with time (from 0.32 to 0.36%) and, as a result, the decreasing trend in C/N ratio (from 12 to 10).

Long-term Effects of Crop Rotation and Different Fertilization Systems on Soil Fertility and Productivity

Long-term Effects of Crop Rotation and Different Fertilization Systems on Soil Fertility and Productivity

Long-term crop rotations affect soybean yield, seed weight, and soil chemical properties

Crop rotation is an important management practice in the production of soybean ( Glycine max (L.) Merr.). For the eastern Great Plains, more information is needed to determine whether current crop rotations are sustainable for soybean production over a long-term period. A field study was conducted in southeastern Kansas from 1979 to 1998 on a Parsons silt loam soil (fine, mixed, thermic, Mollic Albaqualf) to evaluate long-term effects of crop rotation on soybean yield, seed weight, and soil chemical properties. Treatments consisted of three 2-years rotations and one monoculture system: (1) W– S/ S=( winter wheat (Triticum aestivum L.)– soybean doublecrop )/ full- season soybean ; (2) W– Fal/ S=( winter wheat – summer fallow )/ full- season soybean ; (3) GS/ S= grain sorghum (Sorghum bicolor ( L.) Moench)/ soybean ; (4) S/S=continuous soybean. Full-season soybean yields were compared across all treatments in even-numbered years. On average, crop rotation increased soybean yields 16% compared to monoculture soybean. Full-season soybean yields averaged 1.91 Mg ha −1 following wheat–double-cropped soybean, 2.09 Mg ha −1 following wheat–summer fallow, 1.99 Mg ha −1 following grain sorghum, and 1.68 Mg ha −1 following soybean. Soybean seed weights were also significantly greater in most years when grown in rotation compared to monoculture soybean. Crop rotation increased total soil C and total soil N concentrations by 25% in the upper soil profile compared to monoculture soybean. Differences in soil values among crop rotations were directly proportional to the total quantity of above-ground crop residues produced. On average, W–S/S, W–Fal/S, and GS/S rotations produced more than 8 Mg ha −1 of above-ground crop residues for each 2-years cropping cycle compared with only 3 Mg ha −1 for S/S. In the short-term, benefit of crop rotation was increased soybean yield, which would likely increase soybean profitability. In the long-term, rotations with high residue-producing crops, such as wheat and grain sorghum, significantly increase total soil C and N concentrations over time, which may further improve soil productivity.

Long-Term Crop Rotation Effects on Organic Carbon, Nitrogen, and Phosphorus in Haplustoll Soil Fractions

Soil organic matter (SOM) or carbon (SOC) consists of a number of fractions (which can be separated by granulometric wet sieving) having different properties among them. Information on fraction nutrient distribution and long-term crop rotations is lacking for semiarid environments. The objective of this research was to study the agronomic effects on soil OC, N, and P fractions. The humified OC was the largest and least variable fraction of the SOC. Soil under continuous mixed pasture had higher OC contents than under annually tilled treatments. Similarly, soil total nitrogen under the cropped treatments decreased from 1.7 g N kg-¹ in noncultivated soils (reference plots) to 1.0, 0.7 an 0.7 g N kg-¹ under mixed pasture, pasture-crop, and wheat-crop respectively, in the fine soil fraction. The reference plots also showed significantly lower levels of organic phosphorus (P o ) in comparison to the other treatment (from 67.1 w g P o g-¹ to greater than 100 w g P o g-¹ in the fine fraction of the treatments and years). The noncultivated soil showed larger values of P o and inorganic P in the large-size granulometric fraction (0.1-2 mm) than in the soil fine fraction (0-01 mm). However, the rotation treatments had greater concentrations of P in the fine fraction. The P o from the coarse fraction appears to be the most labile and sensitive fraction to tillage and environmental conditions, and may be closely related to P availability.