Stabilised carbon in subsoil horizons is located in spatially distinct parts of the soil profile

Soil organic matter (SOM) stabilisation in subsoil horizons received much attention in recent years, due to the presence of compounds with very long residence times. The reasons for enhanced organic carbon stabilisation in subsoil horizons are poorly understood. In this study, we characterised SOM in adjacent soil compartments with different pedological functioning. We sampled SOM in visually identifiable zones in form of tongues and the adjacent soil matrix from deep soil horizons (60-140 cm depth) of 3 profiles under agricultural land. The samples were analysed for elemental and isotopic composition, radiocarbon age, chemical composition and lignin signature. The objective of the study was to examine if the tongues are characterised by contrasting carbon amounts and composition with regards to the soil matrix.Our results indicate that tongues have two times higher carbon content and are depleted in ¹⁵N with regards to the adjacent soil matrix. SOM in the tongues is characterised by up to modern radiocarbon ages, whereas SOM in the adjacent soil matrix is several thousand years old. Twenty percent more HF soluble carbon in the soil matrix suggest that more mineral bound, highly mobile SOM is present compared to tongues. Differences in chemical composition concern the lignin component, which seems to be preserved in the soil matrix. These data may be explained by different functioning in the two parts of the soil profile. In tongues, fresh carbon input by preferential flow and/or roots may lead to higher SOM turnover compared to the soil matrix. This heterogeneous distribution of stabilised SOM must be taken into account, when studying carbon sequestration in deep soil horizons.     

Risk assessment of subsoil compaction for arable soils in Northwest Germany at farm scale

The physically defined concept “precompression stress (Pc)” is presented at farm scale, including two operation methods in order to define precaution and critical values for the legislation and executive level according to the German Soil Protection Law. The first step is the prevention of subsoil compaction in general by the definition of the mechanical strength of soils, which is defined by the Pc. This Pc value is used as the precaution value, to ensure site-adjusted land use. The second step is to predict the change of soil functions after exceeding the Pc and furthermore to assess if critical values (test and action values) caused by subsoil compaction are reached or already exceeded. Criteria for the definition of critical values by subsoil compaction concerning crop production are discussed in order to also establish such values in the European Soil Framework Directive. The “Pc” concept, which includes predicted and regionalized “Pc”-maps, was verified on a research farm in the weichselian moraine landscape in Northern Germany for areas resistant or susceptible to soil deformation at the given water content throughout the year. Furthermore, the stress-dependent changes of the air capacity after exceeding the Pc was predicted by pedotransfer functions and linked with the farm soil map. As an additional proof for the validity of the Pc concept, a field experiment on a Stagnic Luvisol was also conducted in order to measure the stress distribution up to 60 cm depth using the Stress State Transducer (SST) system at two different wheel loads (3.3 and 6.5 Mg) using a tractor-pulled mono-wheeler. According to the effective soil strength, the wheel load should not exceed 3.3 Mg at field capacity to avoid subsoil compaction.     

Seedbed compaction produced by traffic on four tillage regimes in the rolling Pampas of Argentina

The main function of primary tillage is to increase the soil's structural macro-porosity, but during secondary tillage operations over these freshly tilled soils, traffic causes significant soil compaction. In terms of soil conservation however, there is evidence that direct sowing is a more sustainable system, even though there is still insufficient information about the rheology of a non-tilled soil under traffic. The objective of this study was to compare the traffic intensity and soil compaction caused by four different tillage regimes currently used by Argentinean farmers (1 direct sowing with a tractor and planter weighing 127 kN and 3 conventional tillage systems with equipment weighing 55.2 kN). The work was performed in the east of the Rolling Pampa region, Buenos Aires State, Argentina at 34°25′S, 59°15′W. Variables measured were: (1) cone index in the 0–450 mm depth profile; (2) bulk density; (3) total soil porosity; and (4) rut depth. (a) Results indicated that in the depth range 0–150 mm with all tillage treatments, bulk density and cone index values generated by tractor traffic were greater than the 1.3 Mg m⁻³ and 1400 kPa respectively. Similarly in deeper layers these parameters were greater than 1.45 Mg m⁻³ and 2000 kPa respectively. Measurements revealed that traffic reduced topsoil porosity under direct sowing by an average of 7% and under conventional tillage by 7.6–14.8% confirming that both systems cause both topsoil and subsoil compaction.     

Amelioration of dense sodic subsoil using organic amendments increases wheat yield more than using gypsum in a high rainfall zone of southern Australia

Subsoil constraints are major limiting factors in crop production in many soils of southern Australia. A field study examined effects of deep incorporation of organic and inorganic amendments in 30–40 cm on soil properties, plant growth and grain yield of wheat (Triticum aestivum var. Ambrook) on a Sodosol with dense sodic subsoil with or without lucerne history in a high rainfall region (long-term average annual rainfall 576 mm) of Victoria. Amendments were applied at a rate of 10–20 t ha⁻¹. Deep ripping alone and deep ripping with gypsum did not significantly affect grain yields. In comparison, application of organic materials doubled biomass production and increased grain yield by 1.7 times. Organic amendment-treated plots produced 60% more grains per area than the untreated control. The crop extracted over 50 mm extra water from below 40 cm soil in organic amendment-treated plots than the untreated control. Nitrogen uptake was almost doubled (403 kg ha⁻¹) in the organic amendment-treated plots than the untreated control (165 kg ha⁻¹). The improved yield with amendments was related to an increase in plant available water in the hostile subsoil, and prolonged greenness of leaves and supply of nitrogen and other nutrients.     

实施玉米推茬清垄精播技术 实现高产高效与环境友好生产

实现玉米高产高效、环境友好是当前玉米生产技术发展的重要方向。针对玉米耕层障碍、秸秆处理难和群体质量差三大难题,中国农业科学院作物科学研究所研发出了玉米推茬清垄精播技术。该技术在前茬秸秆堆积地块,可对播种带的行内进行推茬清垄、播种带中间深松、深层施肥、小双行错位精量播种等多项作业过程,通过机械一次性完成,构建了玉米以推茬清垄精播为特点的机械化密植轻简栽培技术体系。在我国玉米主产区进行该技术示范推广,证明该技术可改善土壤耕层条件,提高玉米免耕直播的播种质量,并提高作业效率、减少能量消耗及预防秸秆焚烧,实现了玉米增产、降本、控焚烧的良好效果。     

不同磷物料培肥心土对大豆产量和品质的影响

为明确黑土心土培肥不同磷物料效果,通过小区比对试验方法,采用自主研发的土壤深耕犁和心土培肥犁分别对嫩江薄层黑土进行心土培肥试验,比较5种不同磷肥(P_2O_5含量22.5%的磷矿粉、44%的磷酸一铵、28%的磷矿粉、46%的重过磷酸钙、12%的过磷酸钙)心土培肥效果,明确了不同磷物料心土培肥对大豆生育性状、产量及品质的影响。结果表明:不同磷物料对大豆生育及产量影响差异显著,盛花期和结荚期叶绿素含量也有显著差异,综合比较P_2O_5含量44%的磷酸一铵处理增产效果最显著,比对照组增产32.79%,且大豆叶绿素含量、干物质重量比对照提高9.7%和35.5%,蛋白质含量提高3.45%,同时高于其它磷物料培肥处理,因此心土培肥应根据生产实际条件选择相应的培肥物料,更加利于大豆产量的提高。     

不同底土铺植马尼拉草坪效果比较研究

采用稻田土、原土、黄心土、淤沙土4种不同底土铺植马尼拉草坪,通过对不同底土铺植地块的杂草种类和株数、草坪景观效果、抗性、草坪管理等指标的比较,发现用黄心土铺植马尼拉草坪效果较好,有杂草种类和株数少、景观效果好、抗病抗旱性强、管理费用低等优点。