Phosphorus leaching from clay soils can be counteracted by structure liming

Two field experiments with drained plots on clay soils (60 and 25 % clay) demonstrated a significant reduction in leaching of total phosphorus after application of structure lime. Aggregate stability, was significantly improved. Phosphorus leaching in particulate form was significantly reduced following structure liming at the site with a very high clay content. Sites representing low (50 mg kg-1) and high (140 mg kg-1) levels of phosphorus extractable with acid ammonium lactate in topsoil displayed differing effects on leaching of dissolved reactive phosphorus. This form of phosphorus was only significantly reduced compared with the control at one site with high topsoil phosphorus status and relatively high (17-18%) degree of phosphorus saturation in the subsoil. Laboratory experiments with simulated rain events applied to topsoil lysimeters from the same site also demonstrated a significant reduction in leaching of dissolved reactive phosphorus. These findings indicate that structure liming is an appropriate leaching mitigation measure on soils with both a high clay content and high soil phosphorus status

Mitigation of phosphorus leaching losses via subsurface drains from a cracking marine clay soil

In Scandinavia, subsurface transport via tile drains contributes significantly to phosphorus (P) and nitrogen (N) leaching from arable land, which adds to the eutrophication of surface waters. Using flow-proportional water sampling, various options for mitigating subsurface P leaching losses (and N leaching) were examined in 28 experimental plots on a flat, tile-drained site with 60% marine clay. Two crop rotations and unfertilised fallow were monitored for a total of six years. In addition to topsoil management practices (different forms of tillage, structural liming and mineral P fertilisation), local spatial variations in subsurface transport were determined within the experimental area. Mean total P (TotP) leaching losses after conventional autumn ploughing and inverting the soil to a depth of 23 cm were 0.79 kg ha-1 year-1, with 87% occurring as particulate P (PP), and the corresponding mean total N leaching losses were 27 kg ha-1 year-1, with 91% occurring as nitrate. The coefficient of variation in TotP leaching both in spring before the experiment started (64%) and during the six-year experiment (60%) was higher than the coefficient of variation in P-soil status (20%), or drainage (25%), illustrating the importance of local-scale subsurface transport in this cracking clay. However, TotP and PP leaching losses were significantly (pr>FF <0.001) lower from unfertilised fallow than from other treatments and was not significantly lower after shallow autumn tillage than after conventionally ploughing, whereas PP losses tended to be higher. Infiltration measurements with tension infiltrometers revealed a high variation in saturated hydraulic conductivity within plots. In view of the generally high PP losses, efforts to combat eutrophication of the nearby Baltic Sea should concentrate on soil structure improvements, while extensive tillage and totally omitting P fertilisation of cracking soils with low soil P status appears to be inefficient mitigation options

Structure liming enhances aggregate stability and gives varying crop responses on clayey soils

It has been suggested that liming can improve soil structure and thereby decrease losses of particles and associated nutrients. In this study, two types of structure lime, slaked lime (Ca(OH)(2)) and a mixed product of calcium carbonate (CaCO3) and slaked lime (Ca(OH)(2)), were applied at three different rates in field trials on clayey soils (23%-40% clay). A combination of primary tillage and structure liming was also studied, in a split-plot trial on a clayey soil (25% clay). Aggregate (2-5mm) stability, measured as reduction in turbidity (which is strongly correlated with losses of particulate phosphorus), was significantly increased with the highest application rates of both structure lime products. Aggregate size distribution was also improved with structure lime, creating a finer tilth in the seedbed. Yield response to structure lime was not consistent, with both negative and positive responses over the four-year study period. Positive yield responses can possibly be attributed to the finer tilth preventing evaporation in two dry growing seasons. Negative yield responses were probably an effect of impaired phosphorus availability associated with limited precipitation in May-July in 2011 and 2013. Two years after liming, soil pH levels were significantly elevated in plots with the highest application rate of structure lime, whereas no significant increases were found three years after liming. However, a lingering effect of liming was still detectable, as manganese concentration in barley grain was significantly lower in plots with the highest application rates of both structure lime products in the fourth study year. These results indicate that structure liming can be used as a measure to mitigate phosphorus losses from clayey soils, thereby preventing eutrophication of nearby waters. However, the yield response was varying and unpredictable and thus further investigations are needed to determine the circumstances in which field liming can act efficiently not only to prevent phosphorus losses, but also to ensure consistent yield increases

Changes in pore networks and readily dispersible soil following structure liming of clay soils

Structure liming aims to improve soil structure (i.e., the spatial arrangement of particles and pores) and its stability against external and internal forces. Effects of lime application on soil structure have received considerable interest, but only a few studies have investigated effects on macro- and mesopore networks. We used X-ray computed tomography to image macropore networks (phi >= 0.3 mm) in soil columns and mesopores (phi > 0.01 mm) in soil aggregates from three field sites with (silty) clay soils after the application of structure lime (3.1 t ha(-1) or 5 t ha(-1)- of CaO equivalent). Segmented X-ray images were used to quantify soil porosity and pore size distributions as well as to analyse pore architecture and connectivity metrics. In addition, we investigated the amount of readily dispersible soil particles. Our results demonstrate that structure liming affected both, macropore networks and amounts of readily dispersible soil to different degrees, depending on the field site. Significant changes in macropore networks and amounts of readily dispersible soil after lime application were found for one of the three field sites, while only some indications for similar changes were observed at the other two sites. Overall, structure liming tended to decrease soil macroporosity and shift pore size distribution from larger (epsilon( >100 mm) ) and medium sized macropores (epsilon( 0.3-1.0) (mm)) towards smaller macropores (epsilon( 0.1-0.3) (mm)). Furthermore, liming tended to decrease the critical and average pore diameters, while increasing the surface fractal dimension and specific surface area of macropore network. Structure liming also reduced the amounts of readily dispersible soil particles. We did not find any changes in mesopore network properties within soil aggregates or biopore networks in columns and aggregates. The effects of lime on macropore networks remain elusive, but may be caused by the formation of hydrate phases and carbonates which occupy pore space

Long-term evidence for ecological intensification as a pathway to sustainable agriculture

Ecological intensification (EI) could help return agriculture into a 'safe operating space' for humanity. Using a novel application of meta-analysis to data from 30 long-term experiments from Europe and Africa (comprising 25,565 yield records), we investigated how field-scale EI practices interact with each other, and with N fertilizer and tillage, in their effects on long-term crop yields. Here we confirmed that EI practices (specifically, increasing crop diversity and adding fertility crops and organic matter) have generally positive effects on the yield of staple crops. However, we show that EI practices have a largely substitutive interaction with N fertilizer, so that EI practices substantially increase yield at low N fertilizer doses but have minimal or no effect on yield at high N fertilizer doses. EI practices had comparable effects across different tillage intensities, and reducing tillage did not strongly affect yields.Intensifying food production sustainably is critical given growing demand and agriculture's environmental footprint. This meta-analysis finds that practices such as adding organic matter and increasing crop diversity can partly substitute for nitrogen fertilizer to sustain or increase yields

Jordpackningens verkan på grödan under olika väderleksförhållanden

Markpackning har varit ett stort problem allt sedan mekaniseringen och intensifieringen av växtproduktionen. För att karlägga olika jordars och grödors packningskänslighet utförde avdelningen för jordbearbetning vid institutionen för markvetenskap, SLU, omfattande ettåriga markpackningsförsök mellan åren 1969 till 1981. Antalet försök uppgick till över 100 och var fördelade över hela landet. I de flesta försök ingick fyra led (ingen packning, lätt packning, normal packning och stark packning). Packningsskadorna karakteriserades med hjälp av den S.k. packningsgraden (D). Denna definieras som jordens torra skrymdensitet i fält i % av torra skrymdensiteten i samma jord sedan den på laboratoriet packats med en vertikal tryck av 200 kPa. I en nyplöjd mineraljord är D omkring 65 och måste återpackas för att förbättra jord/rot kontakt och kapillär ledningsförmåga för vatten. Är D omkring 100, så är jorden starkt packad. Den optimala packningsgraden för kom, som var försöksgröda i studierna som redovisas här, ligger omkring 87. Vid utförandet av försöken följdes ett likartat schema. Det förekom dock variation i packning s grads optimet från år till år för ett flertal försöksplatser och serier. Den främsta orsaken till de varierande resultaten mellan åren kan ha varit att väderleken under vegetationsperioden varierade. Med denna hypotes analyserade vi skörderesultat från 53 försök med vårsådda grödor genom att använda mark- och väderleksdata. Föreliggande rapport omfattar följande serier: jordpackning i vårsäd (R2-7204, 13 försök), olika jordars packningskänslighet (R2- 7210, 24 försök), Jordpackning - olika koms orter (R2-7211 & 7212, 9 försök), vårsådda grödors packningskänslighet (R2-7213, 3 försök), ettåriga packningsförsök i kom (R2-7214, 4 försök). Från mark- och klimatdata simulerades markens vattenhalt under vegetationsperioden. Data för nederbörd, lufttemperatur, vindhastighet och relativ fuktighet erhölls från närliggande klimatstationer. För simuleringen av markens vattenhalt användes COUPMode1 . Med hjälp av de erhållna simuleringsresultaten och packnings graden bedömdes om det hade inträffat en kritisk situation vad gällde syre- och vatten/näringsbrist och om markens penetrationsmotstånd hade varit för hög. Resultat av statistisk analys visade att de mest betydelsefulla faktorer för inverkan av packningsgraden på skörden var vattenhalt vid packning> såtid> extrem torka under vegetationsperiod> tillfälligt vattenbrist> för hög markfuktighet (syrebrist) under vegetations perioden. Hög vattenhalt vid packningen resulterade i hög packningsgrad men den hade mindre betydelse för skördesänkningen. Tidig sådd i många försök mildrade den negativa inverkan av packningen särskilt under extrem torra växtsäsonger, då nederbörden var så låg att markens vattenhalt minskade kraftigt under hela vegetationsperioden. Annars orsakade långvarig vattenbrist stora skördesänkningar i hårt packade led. Däremot observerades stigande skörd med ökande packning s grad om det hade varit korta perioder med vattenbrist. Det orsakade förskjutning av packningsgradsoptimet. Högst avkastning erhölls för 55 % av de här rapporterade försöksresultaten vid den så kallad packningsgradsoptimum (omkring 87 för kom). Trendanalys indikerade att den siffran kunde ha varit betydligt högre om man vid packningsförsöket hade lyckats skapa packningsgardsoptimet i alla försök

Markfysikaliska studier i långliggande försök med reducerad jordbearbetning

The minimum possible soil tillage is an important part of a sustainable crop production system. Research and practice of reduced tillage was originally started mainly to reduce energy and time consumption related to tillage. However, current research and practice of reduced tillage is also aimed at soil and water conservation as well as reduction of nutrient losses from arable land. Research on reduced tillage in Sweden has been conducted for more than two decades. Reduced tillage comprises different tillage systems, which replace the traditional moldboard ploughing. These also include modem plough shares by which depth of ploughing can be reduced to about 10 cm. This report summarizes investigations of soil physical properties in six long-term experiments with reduced tillage. The experiments were 6 to 24 years old at the time of investigation (in 1997 or 1998). In this study, soil physical properties after minimum tillage and conventional ploughing were compared. Soil physical properties investigated include dry bulk density , soil water content during the vegetation period, infiltration, saturated hydraulic conductivity, water holding capacity, air permeability in the field and laboratory, oxygen content of soil air after continuous or heavy rain, and soil temperature. Soil water content during the vegetation period was measured with TDR (Time Domain Reflectometry). The dry bulk density in the lower part of the top soil was greater in plots with reduced tillage than in plots with conventional ploughing. Many of the investigated soil physical properties were improved by reduced tillage. Variation of soil water content was smaller for reduced tillage than for conventional ploughing. This shows that drainage and water holding capacity often were improved, particularly in the heavy soils. crop yield in heavy clays has been improved by reduced tillage. In some cases, A decrease in yield was observed during the initial periods of reduced tillage, but the difference has been minimized with time, which can be attributed to the improvement of soil structure. This improvement, however, may be less pronounced in light soils. A well planned transition from conventional ploughing to reduced tillage, such as loosening of old plough pan and minimizing of infestation by perennial weeds, can minimize yield losses