Effects of Broad-Leaf Crop Frequency in Various Rotations on Nitrate Nitrogen and Extractable Phosphorus in a Black Chernozem Soil

In the Canadian prairies, current recommendations allow growing of canola or pea once every 4 years on a particular field to effectively mange diseases, insects, and weeds, but producers are interested in increasing frequency of these crops to optimize economic returns. A 4-year (from 1999 and 2002) field experiment, with treatments consisting of rotations of monoculture canola and pea to rotations that contained these crops every 2, 3, and 4 years with wheat and flax, was conducted on a Black Chernozem (Udic Boroll) silty clay at Melfort, Saskatchewan, to determine the impact of frequency of broad-leaf crops canola and pea in various crop rotations on accumulation and distribution of nitrate nitrogen (N) and extractable phosphorus (P) in the soil profile after 4 years. Two cultivars of canola, an herbicide-tolerant blackleg- resistant variety (hybrid) and a conventional (not herbicide tolerant) open-pollinated, blackleg-susceptible variety (OP), were included. Mean effects of crop rotation or rotation length on soil nitrate N were not significant, though the amount of soil nitrate N in different soil layers tended to be greatest with monocultures and least in the 4-year rotation with flax. Effects of crop phase (i.e., individual crops that make up the rotation)?×?crop rotation interactions on soil nitrate N were significant for all layers in the soil profile. The amounts of nitrate N in soil after canola, especially hybrid canola, were lowest in most crop rotations, suggesting the importance of canola in minimizing downward movement of nitrate N in the soil profile. Soil extractable P in the 0- to 15-cm layer was least with monocultures and greatest in the 4-year rotation with flax. There was a significant effect of crop phase on soil extractable P, but soil P levels varied with crop phase in different rotations. In conclusion, residual nitrate N in soil can be reduced by extending crop rotations and using high-yielding disease-resistant canola cultivars, most likely by improving crop yields.     

Soil residual nitrogen under various crop rotations and cultural practices

Crop rotation and cultural practice may influence soil residual N available for environmental loss due to crop N uptake and N immobilization. We evaluated the effects of stacked vs . alternate‐year crop rotations and cultural practices on soil residual N (NH₄‐N and NO₃‐N contents) at the 0–125 cm depth, annualized crop N uptake, and N balance from 2005 to 2011 in the northern Great Plains, USA. Stacked rotations were durum (Triticum turgidum L.)–durum–canola (Brassica napus L.)–pea (Pisum sativum L.) (DDCP) and durum–durum–flax (Linum usitatissimum L.)–pea (DDFP). Alternate‐year rotations were durum–canola–durum–pea (DCDP) and durum–flax–durum–pea (DFDP). Both of these are legume‐based rotations because they contain legume (pea) in the crop rotation. A continuous durum (CD) was also included for comparison. Cultural practices were traditional (conventional tillage, recommended seeding rate, broadcast N fertilization, and reduced stubble height) and improved (no‐tillage, increased seeding rate, banded N fertilization, and increased stubble height) systems. The amount of N fertilizer applied to each crop in the rotation was adjusted to soil NO₃‐N content to a depth of 60 cm observed in the autumn of the previous year. Compared with other crop rotations, annualized crop biomass N was greater with DCDP and DDCP in 2007 and 2009, but was greater with DDFP than DCDP in 2011. Annualized grain N was greater with DCDP than CD, DFDP, and DDFP and greater in the improved than the traditional practice in 2010 and 2011. Soil NH₄‐N content was greater with CD than other crop rotations in the traditional practice at 0–5 cm, but was greater with DDCP than CD and DDFP in the improved practice at 50–88 cm. Soil NO₃‐N content was greater with CD than other crop rotations at 5–10 cm, but was greater with CD and DFDP than DCDP and DDCP at 10–20, 88–125, and 0–125 cm. Nitrate‐N content at 88–125 and 0–125 cm was also greater in the traditional than the improved practice. Nitrogen balance based on the difference between N inputs and outputs was greater with crop rotations than CD. Increased N fertilization rate increased soil residual N with CD, but legume N fixation increased N balance with crop rotations. Legume‐based crop rotations (all rotations except CD) reduced N input and soil residual N available for environmental loss, especially in the improved practice, by increasing crop N uptake and N immobilization compared with non‐legume monocrop.     

Arbuscular mycorrhizal fungi and soil aggregation in a no‐tillage system with crop rotation

Crop rotation adoption in no‐tillage systems (NTS) has been recommended to increase the biological activity and soil aggregation, suppress soil and plant pathogens, and increase the productivity aiming at the sustainability of agricultural areas. In this context, this study aimed to assess the effect of crop rotation on the arbuscular mycorrhizal fungi (AMF) community and soil aggregation in a soil cultivated for nine years under NTS. Treatments consisted of combinations of three summer crop sequences and seven winter crops. Summer crop sequences consisted of corn (Zea mays L.) monoculture, soybean (Glycine max L. Merrill) monoculture, and soybean–corn rotation. Winter crops consisted of corn, sorghum (Sorghum bicolor (L.) Moench), sunflower (Helianthus annuus L.), sunn hemp (Crotalaria juncea L.), pigeon pea (Cajanus cajan (L.) Millsp.), oilseed radish (Raphanus sativus L.), and millet (Pennisetum americanum (L.) Leeke). Soil samples were collected at a depth of 0–0.10 m for analyses of soil chemical, physical, and biological attributes. Spore abundance, total glomalin, and soil aggregate stability index were higher in the soil under corn monoculture. The highest values of aggregate mean weight diameter were observed in the soybean–corn rotation (3.78 mm) and corn monoculture (3.70 mm), both differing from soybean monoculture (3.15 mm), while winter crops showed significant differences only between sorghum (3.96 mm) and pigeon pea (3.25 mm). Two processes were identified in the soil under summer crop sequences. The first process was observed in PC1 (spore abundance, total glomalin, easily extractable glomalin, pH, P, and Mg²⁺) and was related to AMF; the second process occurred in PC2 (aggregate mean weight diameter, soil aggregate stability index, K⁺, and organic matter) and was related to soil aggregation. The nine‐year no‐tillage system under the same crop rotation adoption influenced AMF abundance in the soil, especially with corn cultivation in the summer crop sequence, which promoted an increased total external mycelium length and number of spores of AMF. In addition, it favored an increased soil organic matter content, which is directly related to the formation and stability of soil aggregates in these managements.     

Influence of current and previous crops on soil basal and potential denitrification rates

Soil and crop management including crop rotation influences available organic carbon and soil nitrate levels, which may in turn affect denitrification losses from soils. The objective of this paper was to determine how the current and previous crop affect denitrification by comparing the basal denitrification rate (BDR), denitrification rate with added nitrate (DAN), and potential denitrification rate (PDR) (amended with glucose and nitrate) of a clay loam soil under monoculture corn (C), soybean (S), and winter wheat (WW) with or without underseeded red clover (RC) and under each phase of a 2-year crop rotation (C-S) and two 3-year crop rotations (C-S-WW, C-S-WW+RC). The BDRs were greater in the 3-year C-S-WW rotation treatments than in the 2-year C-S rotation and monoculture C, S, and WW treatments. The WW+RC phase of the C-S-WW+RC treatment was found to have a greater BDR and DAN than the corn phase of the rotation. Available organic carbon was found to limit denitrification in the BDR and DAN incubations as evidenced by the 2- to 21-fold increase in denitrification when glucose was added in the PDR assay. Further, the significant relationship between soil respiration and BDR suggests that available carbon was a limiting factor. This study found that both the current crop and previous crops in a rotation affected soil denitrification rates substantially; and that denitrification rate was increased when a mixture of crop residues were added to soil (i.e., from growing crops in rotation) relative to when only a single residue was added (i.e., monoculture cropping).     

Rotation and tillage effects on available soil water for winter wheat in a semi-arid environment

The recent adoption of conservation farming systems in the semi-arid Canadian prairies opens up the possibility of replacing the traditional fallow period with non-cereal crops (oilseeds, legumes). However, information on changes to soil water regimes by inclusion of these crops, especially in combination with zero tillage, is sparse. A study was initiated in 1984 on a sandy clay loam soil at Lethbridge, Alberta, to investigate the performance of winter wheat (Triticum aestivum L.) under conventional, minimum and zero tillage in monoculture and in 2-year rotations with fallow, canola (Brassica campestris L.) or lentils (Lens culinaris Medic.)/flax (Linum usitatissimum L.). Conventional tillage in the Lethbridge region is shallow cultivation (10 cm) with a wide-blade (sweep) cultivator. Continuous cropping greatly depleted soil water reserves, resulting in some crop failures. Averaged over 10 years, available water for establishment of winter wheat in fall was least after canola (45 mm), followed by continuous winter wheat (59 mm), lentils/flax (74 mm) and fallow (137 mm). In this semi-arid region, the effect of rotation on soil water was much greater than that of tillage. Zero tillage had relatively little impact on available water to 1.5 m depth. However, once the experiment had been established for 6–7 years, available water in the 0–15 cm depth under winter wheat in spring was greatest under zero tillage. Precipitation storage efficiency during the fallow year was generally unaffected by tillage system.     

Contributions from carbon and nitrogen in roots to closing the yield gap between conventional and organic cropping systems

This study investigates the effect of different crop rotation systems on carbon (C) and nitrogen (N) in root biomass as well as on soil organic carbon (SOC ). Soils under spring barley and spring barley/pea mixture were sampled both in organic and conventional crop rotations. The amounts of root biomass and SOC in fine (250–253 μ m), medium (425–250 μ m) and coarse (>425 μ m) soil particulate organic matter (POM ) were determined. Grain dry matter (DM ) and the amount of N in harvested grain were also quantified. Organic systems with varying use of manure and catch crops had lower spring barley grain DM yield compared to those in conventional systems, whereas barley/pea showed no differences. The largest benefits were observed for grain N yields and grain DM yields for spring barley, where grain N yield was positively correlated with root N. The inclusion of catch crops in organic rotations resulted in higher root N and SOC (g C/m²) in fine POM in soils under barley/pea. Our results suggest that manure application and inclusion of catch crops improve crop N supply and reduce the yield gap between conventional and organic rotations. The observed positive correlation between root N and grain N imply that management practices aimed at increasing grain N could also increase root N and thus enhance N supply for subsequent crops.     

Effects of tillage method and crop rotation on non-renewable energy use efficiency for a thin Black Chernozem in the Canadian Prairies

Producers in the Canadian Prairies have begun to extend and diversify their cereal-based rotations by including oilseed and pulse crops, and by managing these newer cropping systems with minimum- and zero-tillage practices. This study examined the implications of these land use changes on non-renewable energy requirements (both direct and indirect), energy output, and energy use efficiency for monoculture cereal, cereal–oilseed, and cereal–oilseed–pulse rotations, each managed using conventional (CT), minimum (MT), and zero (ZT) tillage practices on a thin Black Chernozem in Saskatchewan, Canada. The crop rotations included: spring wheat (Triticum aestivum L.)–spring wheat–winter wheat–fallow (Ws–Ws–Ww–F), spring wheat–spring wheat–flax (Linum usitatissimum L.)–winter wheat (Ws–Ws–Fx–Ww), and spring wheat–flax–winter wheat–field pea (Pisum sativum L.) (Ws–Fx–Ww–P). The findings, based on 12 years of data, showed that non-renewable energy use for the complete cropping systems was largely unaffected by tillage method, but that it differed significantly with crop rotations. Energy requirements were lowest for Ws–Ws–Ww–F (average 6389 MJ ha⁻¹), intermediate for Ws–Fx–Ww–P (11% more), and highest for the Ws–Ws–Fx–Ww (28% more). The substitution of pea for spring wheat in the Ws–Fx–Ww–P versus Ws–Ws–Fx–Ww rotation reduced total energy use by 13%, reflecting the minimal requirement for N fertilizer by pulses due to their ability to biologically fix N, and from the lower fertilizer N rate that was applied to spring wheat grown after the legume. The use of MT and ZT practices provided significant energy savings (compared to CT) in on-farm use of fuel and in machine operation and manufacture for some cropping system components (e.g., summerfallow preparation, spring wheat grown on pea stubble, and for pea grown on cereal stubble), but these savings were often offset by higher energy requirements for herbicides and for N fertilizer with conservation tillage management. Gross energy output averaged 32 315 MJ ha⁻¹ for Ws–Ws–Ww–F, 41 287 MJ ha⁻¹ (or 28% more) for Ws–Ws–Fx–Ww, and 42 961 (or 33% more) for Ws–Fx–Ww–P. Tillage method had little overall influence on energy output for the monoculture cereal and cereal–oilseed–pulse rotations, but it was generally lower with CT than with MT or ZT management for the cereal–oilseed rotation. Energy use efficiency, measured as grain produced per unit of energy input and as the ratio of energy output to energy input, was highest for the cereal–oilseed–pulse rotation (373 and 6.1 kg GJ⁻¹, respectively) and lower, but generally similar, for the cereal–oilseed and monoculture cereal rotations (298 and 5.1 kg GJ⁻¹, respectively). The use of conservation tillage management enhanced overall energy use efficiency for the two mixed rotations, but not for the monoculture cereal rotation. We concluded that adopting diversified crop rotations, together with minimum and zero tillage management practices, will enhance non-renewable energy use efficiency of annual grain production in this sub-humid region.     

Comparison of the decomposition and N and P mineralization of canola, pea and wheat residues

Insight into nutrient cycling is gained by understanding the dynamics and quantifying nutrient mineralization from decomposing crop residues. Since wheat (Triticum aestivum L.), canola (Brassica napus L.) and pulse crops such as pea (Pisum sativum L.) are commonly grown in rotation, our objectives were to: (1) compare, using the mesh bag technique, the dry matter (DM) loss and release of N and P of straw and root residues of those crops in the 10-11 months following harvest, and (2) determine the influence of N fertilizer on residue decomposition and nutrient release. The no-tillage study started in autumn 1997 when straw residues were placed on the soil surface and root residues were buried in the soil, and sampled periodically through the 1998 growing season. Wheat was grown in 1998 and received 0 or 60 kg N ha^-1. The study was repeated in 1998/1999. Wheat straw decomposed more slowly than canola or pea straw (losing an average of 12%, 24% and 25%, respectively, of initial DM in 10-11 months), however, the converse was noted for root residues (42%, 26% and 19% of initial DM). Average net N mineralization from wheat, canola and pea straw was essentially 0, 0.7 and 5.6 kg N ha^-1, respectively. Phosphorus released from straw ranged from 0.5 kg ha^-1 for pea to 0.75 kg ha^-1 for canola. Net N and P mineralization from root varied little between crop species: 0.9-1.6 kg N ha^-1 and 0.1-0.3 kg P ha^-1. Nitrogen fertilization increased DM loss, and N and P release from straw residues.     

Nitrate leaching from organic arable crop rotations: effects of location, manure and catch crop

Abstract. Nitrate leaching from crop rotations supporting organic grain production was investigated from 1997 to 2000 in a field experiment at three locations in Denmark on different soil types. Three experimental factors were included in the experiment in a factorial design: (1) proportion of N₂-fixing crops in the rotation (crop rotation), (2) catch crop (with and without), and (3) manure (with and without). Three, four-course rotations were compared, two at each location. The nitrate leaching was measured using ceramic suction cells. Leaching losses from the crop rotation with grass–clover green manure and without catch crops were 104, 54 and 35 kg N ha⁻¹ yr⁻¹ on the coarse sand, the loamy sand, and the sandy loam, respectively. There was no effect of manure application or time of ploughing-in the grass–clover green manure crop on the accumulated nitrate leaching from the entire rotation. Catch crops reduced nitrate leaching significantly, by 30–38%, on the sandy soils. At all locations catch crops reduced the annual averaged nitrate concentration to meet drinking water quality standards in the crop rotation with green manure. On the coarse sand there was a time lag between the onset of drainage and the start of N-uptake by the catch crop.     

Characterization of soil microbial communities under different potato cropping systems by microbial population dynamics, substrate utilization, and fatty acid profiles

The effects of 11 different 2- and 3-yr potato crop rotations on soil microbial communities were characterized over three field seasons using several techniques. Assessments included microbial populations determined by soil dilution plate counts on various general and selective culture media, microbial activity by fluorescein diacetate (FDA) hydrolysis, single carbon source substrate utilization (SU) profiles, and fatty acid methyl ester (FAME) profiles. Potato rotation crops evaluated in research plots at Newport, ME, included barley/clover, canola, green bean, millet, soybean, sweet corn, and a continuous potato control. Soil populations of culturable bacteria and overall microbial activity tended to be highest following barley, canola, and sweet corn rotations, and lowest with continuous potato. Differences among rotations were less apparent during the potato phase of the rotations. Populations of actinomycetes and fluorescent pseudomonads tended to be greater in barley rotations than in most other rotations. SU profiles derived from BIOLOG GN2 plates indicated that certain rotations, including barley, canola, and sweet corn tended to have higher overall microbial activity, and barley and sweet corn rotations averaged higher substrate richness and diversity. Soybean and potato rotations tended to have lower substrate richness and diversity. Principal component analyses of SU data revealed differences among rotation soil communities in their utilization of individual carbon sources and substrate guilds, including carbohydrates, carboxylic acids, amines/amides, and amino acids. Analyses of soil FAME profiles demonstrated distinct differences among all the rotation soils in their relative composition of fatty acids, indicating differences in their microbial community structure. Fatty acids most responsible for differentiation among rotation soils included 16:1 ω5c, 16:1 ω7c, 18:2 ω6c, 18:1 ω9c, 12:0, and 13:0 anteiso, with 16:1 ω5c being the single greatest determinant. Overall, monounsaturated fatty acids, particularly 16:1 ω5c, were most prevalent in sweet corn rotations and polyunsaturates were highest in barley and millet rotations. Straight chain saturated fatty acids comprised the greatest proportion of fatty acids in soils under continuous potato. FAME biomarkers for microorganism groups indicated barley and millet rotations had the highest ratio of fungi to bacteria, and soybean and continuous potato had the lowest ratio. This research has demonstrated that different crop rotations have distinctive effects on soil microbial communities that are detectable using a variety of techniques. Further studies will identify more specific changes associated with particular rotations and relate these changes to potential effects on disease management, crop health, and crop productivity.     

Inclusion of upland crops in rice‐based rotations affects chemical properties of clay soil

In the Mekong Delta, alluvial clay soils have been used intensively over many generations for rice monoculture. Currently, farmers are confronted by problems of declining land productivity. Rotations comprising rice and upland crops can increase soil quality, but appropriate cropping systems for paddy soils have received relatively little attention. We therefore established a multiyear field experiment to evaluate the long‐term effects of cropping systems with different rotations on soil chemical quality. Systems laid out in a randomized complete block design with four replications were as follows: (i) traditional rice monoculture with three rice crops per year (R‐R‐R), (ii) rotation with two rice crops and maize (R‐M‐R), (iii) rotation with two rice crops and mung bean (R‐Mb‐R) and (iv) rotation with one rice crop and two upland crops – mung bean and maize (R‐Mb‐M). We hypothesized that systems with rotations of upland crops and their temporary beds improve chemical quality of paddy rice soil. Soil chemical parameters were determined to better understand and evaluate the sustainability of the cropping systems. Results showed an improvement in soil chemical quality for cropping systems with rotations of rice and mung bean or maize grown on temporary beds (R‐M‐R, R‐Mb‐R and R‐Mb‐M), particularly the content of soil organic carbon and a presumed hydrolysable labile carbon fraction compared with rice monoculture. Less pronounced improvements in EC, CEC and total acidity were also found with inclusion of upland crops. Cropping systems of rice with upland crops improved rice grain and straw yield in subsequent season in contrast with rice monoculture.     

Responses of residual and recommended N,P, K,S nutrients and crops to six annual soil test-based fertilizer rates and seeding systems

Responses of residual and recommended nitrogen (N), phosphorus (P), potassium (K), sulfur (S) nutrient amounts and crops (yield, emergence, and height) to 0, 60, 100, and 140% soil test-based fertilizer rate applications on the same plots for six years under minimum tillage and direct seeding systems were assessed. Higher fertilizer rates increased residual nitrate (NO₃)-N, extractable K, and sulfate (SO₄)-S amounts after a low crop yield year, particularly NO₃-N, without temporal trend. Increase in residual available P level at higher fertilizer rates showed a positive temporal trend. Lower N, P, and S fertilizer rates were recommended to crops after higher residual NO₃-N, available P, and SO₄-S levels. Crops effectively used the residual nutrients. Compared to 0%, the relative seed yields at 60, 100, and 140% rates increased with years of fertilization. There were no clear responses of measured soil and crop parameters to seeding systems. Testing residual nutrients can optimize fertilizer use and crop yields.     

Phosphorus and nitrogen turnover and risk of waterborne phosphorus emissions in crop rotations on a clay soil in southwest Sweden

Abstract. Nutrient losses from arable land are important contributors to eutrophication of surface waters, and phosphorus (P) and nitrogen (N) usually act together to regulate production of Cyanobacteria. Concentrations and losses of both nutrients in drainage water from pipe drains were studied and compared in 15 crop rotations on a clay soil in southwest Sweden. Special emphasis was placed on P and it was possible to evaluate critical components of the crop rotations by flow-proportional water sampling. Total P concentrations in drainage water were generally small (0.04–0.18 mg L⁻¹), but during two wetter years out of six, high P concentrations were measured following certain management practices, including ploughing-in lucerne ( Medicago sativa L.) and fertilizing in advance without incorporation into the soil to meet the needs of several subsequent crops. This resulted in average flow-weighted concentrations of total P between 0.3 and 0.7 mg L⁻¹. In crop rotations containing green manures, green fallow or leguminous leys, there was also a risk for increased P losses after these crops were ploughed in. The losses increased in the order: cash crops < dairy with grass < dairy with lucerne < monoculture with barley < organic farming with cattle slurry < stockless organic farming with green manure. P balances varied between −9 and +8 kg P ha⁻¹ and N balances between +4 and +35 kg N ha⁻¹. The balances were not related to actual leaching losses. Phosphorus losses in drainage from set-aside were 67–82% of those from cash crops grown in ploughed and P-fertilized soil at the same site, indicating a high background P loss from this clay soil.     

Effect of Cropping System on Physical Properties of Clay Soil Under Intensive Rice Cultivation

Cropping systems are thought to alter soil quality in paddy rice fields. This study was conducted to quantify the long‐term effects of continuous crop production under different cropping systems with different crop rotations on physical properties of alluvial clay soil in the Mekong Delta, Vietnam. Soil samples were collected from four treatments: (i) traditional intensive rice monoculture with three rice crops per year (R–R–R); (ii) rotation with two rice crops and maize (R–M–R); (iii) rotation with two rice crops and mung bean (R–Mb–R); and (iv) rotation with one rice and two upland crops, mung bean and maize (R–Mb–M). We hypothesized that cropping systems with rotations of upland crops and their temporary beds improve the physical quality of paddy rice soil; hence, they are better options towards sustainable agriculture. Results show an improvement of soil physical quality for systems with two rice crops and one upland crop (R–M–R and R–Mb–R) and those with one rice crop with two upland crops (R–Mb–M) compared with intensive rice monoculture (R–R–R). This was translated in decreased bulk density and soil strength, increased soil organic carbon and total porosity, and higher aggregate stability index, plant‐available water capacity, and Dexter's S index, especially at depths of 10–20 and 20–30 cm. The systems with different upland crops (maize or mung bean) showed similar high physical quality improvement. To maintain soil quality in future seasons, introducing a cropping system with at least one upland crop in rotation with rice is recommended. Copyright © 2014 John Wiley & Sons, Ltd.     

Different crop rotation systems as drivers of change in soil bacterial community structure and yield of rice, <Emphasis Type="Italic">Oryza sativa</Emphasis>

Intensive cropping, especially of rice, is considered to contribute to negative effects not only on soil chemical and biological properties but also on long-term grain yield. Appropriate crop rotation is often practiced as an alternative strategy to overcome the negative side effects of intensive cropping. Although soil microbial diversity and community structure have been shown to respond differently to altered agricultural management practices, little is known about possible links between crop rotation and grain yield on bacterial communities in rice paddy soil. In this study, we investigated the impact of specific rotational crops and compared it with intensive rice cultivation. The main crop rice (Oryza sativa) was rotated with maize (Zea mays) and mungbean (Phaseolus aureus) in different combinations in a system cultivating three crops per year. Soil bacterial communities were studied in two different cropping periods using pyrosequencing of the variable V4 region of the 16S rRNA. Our results showed that rotation with alternative crops increased rice yield by 24–46% depending on rotation structure and that bacterial community structure was altered in the presence of mungbean and/or maize compared to that in rice monoculture. In the crop rotation systems, composition, abundance, and diversity of soil bacterial communities were significantly different and higher than those in rice monoculture. Our results show that effects of crop rotation relate to changes in soil bacterial community structure suggesting that appropriate crop rotations provide a feasible practice to maintain the equilibrium in soil microbial environment for sustainable rice cultivation.     

The effectiveness of cover crops during eight years of a UK sandland rotation

Abstract. Growing cover crops during the winter before spring-planted crops is often suggested as an effective method to decrease nitrate leaching. A four-course crop rotation (potatoes-cereal-sugarbeet-cereal) was followed through two rotations on a sandy soil in the English Midlands. Three management systems were imposed on the rotation to test their effects on nitrate loss. The effects of cover crops on nitrate leaching and crop yields were compared with the more conventional practice of over-winter bare fallow before potatoes and sugarbeet.
Cover crop N uptake was variable between years, averaging 25 kg ha⁻¹, which is typical of their performance on sandy soils in the UK. The cover crops usually decreased nitrate leaching but their effectiveness depended on good establishment before the start of drainage. Over 7 years, cover crops decreased the average N concentration in the drainage from 24 to 11 mg l⁻¹. Potato yield and tuber N offtake increased after cover crops. Ware tuber yield increased by an average of c . 8%; this was unlikely to be due to additional N mineralization from the cover crop because the potatoes received 220–250 kg fertilizer N ha⁻¹, and non-N effects are therefore implicated. Sugar yield was not increased following a cover crop.
After 8 years of nitrate-retentive practices, there were no measurable differences in soil organic matter. However, plots that had received only half of the N fertilizer each year contained, on average, 0.14% less organic matter at the end of the experiment.     

Nitrate leaching from an organic dairy crop rotation: the effects of manure type, nitrogen input and improved crop rotation

Abstract. Four management systems combining high and low livestock densities (0.7 and 1.4 livestock units ha⁻¹) and different types of organic manure (slurry and straw based FYM) were applied to an organic dairy crop rotation (undersown barley – grass–clover – grass–clover – barley/pea – oats – fodder beet) between 1998 and 2001. The effects of the management systems on crop yields and nitrate leaching were measured. In all four years, nitrate leaching, as determined using ceramic suction cups, was higher in the three crops following ploughing of grass–clover than under the barley or grass–clover. Overall, no significant differences in nitrate leaching were observed between the management systems. However, the replacement of the winter wheat crop used in the earlier experimental period (1994–97) by spring oats with catch crops in both the preceding and succeeding winters reduced nitrate leaching compared with the earlier rotation. Increasing the livestock density, which increased manure application by c. 60 kg total N ha⁻¹, increased crop yields by 7 and 9% on average for FYM and slurry, respectively. Yields were 3–5% lower where FYM was used instead of slurry. The experiment confirmed the overriding importance of grassland N management, particularly the cultivation of the ley, in organic dairy crop rotations.     

洱海流域北部农田养分平衡及残留特性研究

为减少农田氮磷流失,改善洱海水质、遏制富营养化发展,以洱海流域北部8个乡（镇）为研究区域,采用现场调查与分析测试相结合的方法研究了洱海流域北部10种典型轮作模式的施肥量、作物养分吸收量、农田养分盈余量以及土壤养分残留状况,对不同轮作模式农田养分平衡及残留特性进行了分析评价。结果表明,水稻-大蒜轮作模式下有机肥和氮肥的投入量显著高于其他模式,水稻-蔬菜作物轮作模式的磷肥投入量显著高于其他模式;不同轮作模式间土壤养分残留差异性以硝态氮最为突出：水稻-大蒜轮作条件下土壤硝态氮残留量达43.4mg.kg-1,明显高于其他轮作模式;10种轮作模式均处于养分盈余状态,以水稻-大蒜轮作模式养分盈余量最大,为1258.8kgN.hm-2和1472.7kgP2O5.hm-2;养分盈余量差异主要凸现在小春季作物上;土壤中易流失的硝态氮、铵态氮和速效磷与氮磷肥的投入量和养分盈余均呈显著相关。表明水稻-大蒜和水稻-蔬菜轮作是洱海流域农田环境污染风险较高的种植模式,需要重点防控。     

Crop production impacts on soil phosphorus removal and soil test levels

An 8-year field study documented the impact of tillage, crop rotations, and crop residue management on agronomic and soil parameters at Brookings, South Dakota. The greatest annual proportion of above-ground biomass phosphorus (P) removed was from the grain (78–87% of total) although crop residue removed some P as well. Greater above-ground total biomass P (grain P + crop residue P) was removed from corn than from soybean and spring wheat crops mainly due to the greater corn grain biomass harvested. Cumulative above-ground biomass P removal was greatest for the corn-soybean rotation (214 kg P ha^?1), while it was lowest for the soybean-wheat rotation (157 kg P ha^?1). Tillage treatments within crop rotation or residue management treatments did not influence annual or cumulative P removal rates. Olsen extractable soil orthophosphate-P levels declined consistently through time from a mean of 40 µg g^?1 (2004) to 26 µg g^?1 (2011). Biomass P removal was calculated to be 15.7 ha^?1 yr^?1 to decrease Olsen extractable soil orthophosphate-P levels by 1 µg g^?1 yr^?1 over 8 years of the study.     

Residual effect and nitrate leaching in grass‐arable rotations: effect of grassland proportion,sward type and fertilizer history

A key point in designing grass‐arable rotations is to find the right balance between the number of cultivations and the length of the grass phase. In a field experiment, we investigated the effect of cropping history (grazed unfertilized grass–clover and fertilized [300 kg N per hectare] ryegrass, proportion of grassland and previous fertilizer use) on crop growth and nitrate leaching for 2 years following grassland cultivation. In the final year, the effect of perennial ryegrass as a catch crop was investigated. The nitrogen fertilizer replacement value (NFRV) of grassland cultivation was higher at 132 kg N per hectare in the rotation with 75% grassland compared with on average 111 kg N per hectare in rotations with 25 and 38% grassland and the NFRV of ryegrass in the rotation was higher than that of grass–clover. Nitrate leaching following cultivation was not affected by the proportion of grassland in the crop rotation or sward type. However, there was a considerable effect of having a ryegrass catch crop following the final barley crop as nitrate leaching was reduced from 60 to 9 kg N per hectare. When summarizing results from the crop rotations over a longer period (1997–2005), management strategy adopted in both the grassland and arable phases appeared to be the primary instrument in avoiding nutrient losses from mixed crop rotations, irrespective of grass proportion. In the arable phase, the huge potential of catch crops has been demonstrated, but it is also important to realize that all parts of the grass‐arable crop rotations must be considered potentially leaky.