Accelerated Degradation and Mineralization of Atrazine in Surface and Subsurface Soil Materials

In surface soils, atrazine is considered to be a moderately persistent herbicide, with half-lives ranging generally from one to two months. In subsoils, however, its degradation is generally slower. This paper reports the degradation of atrazine in soil and subsoil samples taken from six Belgian maize fields. Rapid degradation can take place in some samples taken from surface and in some from subsurface soils. Subsoil samples were found to degrade atrazine either very strongly or not at all. Experiments with [ring-U-¹⁴C] atrazine showed that the micro-organisms responsible for the rapid degradation cleave the triazine ring and extensively mineralize the molecule. © 1997 SCI.     

1ZS-2型振动深松机的研究设计

通过对现有深松机的比较研究，确定了1ZS-2型振动深松机的总体结构；设计了典型零部件并进行了选材和强度校核。该机可通过改变振动元件的转速获得不同的频率，通过改变偏心转子的偏心率来改变振幅。虽然，振动深松不能减少总功耗，但可以大大降低牵引阻力，这对拖拉机充分发挥现有功率是非常有效的。     

振冲碎石桩复合地基在沿海大型原油储备库中的应用

仪征油库15万m3超大型油罐的建造,这在国内尚属首例,油罐采用振冲碎石桩复合地基取得了较为满意的效果。通过介绍该工程地基处理的试桩、试桩检测结果的分析,施工工艺、工程桩检测标准的确定及最后处理效果,为大型油罐地基处理提供了一种效果理想的处理方法。通过对其运用作以介绍,以其对类似工程提供参考。     

Testing the safety-net role of hedgerow tree roots by 15N placement at different soil depths

Trees which root below crops may have a beneficial role in simultaneous agroforestry systems by intercepting and recycling nutrients which leach below the crop rooting zone. They may also compete less strongly for nutrients than trees which root mainly within the same zone as crops. To test these hypotheses we placed highly enriched ¹⁵N-labelled ammonium sulphate at three depths in the soil between mixed hedgerows of the shallow-rooting Gliricidia sepium and the deep rooting Peltophorum dasyrrhachis. A year after the isotope application most of the residual ¹⁵N in the soil remained close to the injection points due to the joint application with a carbon source which promoted ¹⁵N immobilization. Temporal ¹⁵N uptake patterns (two-weekly leaf sub-sampling) as well as total ¹⁵N recovery measurements suggested that Peltophorum obtained more N from the subsoil than Gliricidia. Despite this Gliricidia appeared to compete weakly with the crop for N as it recovered little ¹⁵N from any depth but obtained an estimated 44–58% of its N from atmospheric N₂-fixation. Gliricidia took up an estimated 21 kg N ha^–1 and Peltophorum an estimated 42 kg N ha^–1 from beneath the main crop rooting zone. The results demonstrate that direct placement of ¹⁵N can be used to identify N sourcing by trees and crops in simultaneous agroforestry systems, although the heterogeneity of tree root distributions needs to be taken into account when designing experiments. This revised version was published online in June 2006 with corrections to the Cover Date.     

黄土高原旱作麦田深层土壤水利用与小麦产量及产量稳定性的关系

黄土高原是我国重要旱作农业区,冬小麦是该地区重要的粮食作物之一,如何进一步提高旱作小麦产量并降低由干旱缺水引起的产量波动是该区域未来小麦生产亟待解决的重要问题。由于黄土高原地区冬小麦生育期和降水季节不匹配,土壤水的利用对该区域小麦生产至关重要。基于黄土高原地区以往研究数据,分析表明当前冬小麦产量水平下土壤水利用并不充分;进一步分析表明,1～2 m深层土壤水残留量和产量高度相关,即在冬小麦收获期,当1～2 m深层土壤中有效水残留量为100～130 mm时,冬小麦产量为2 640～4 920 kg·hm^-2,而当残留量减少至30～70 mm时,其产量可显著提高至5 250～6 576 kg·hm^-2;此外,加强深层土壤水利用亦可显著提高高产概率。统计结果表明,在可用水量为666～766 mm(播前0～2 m土层储水量与生育期降水量之和)条件下,收获时如果1～2 m深层土壤水残留量从270～210 mm降低至150～90 mm时,小麦产量高于4 000 kg·hm^-2和5 000 kg·hm^-2的概率可分...     

中国东南部红壤施用石灰和石膏后底土酸性的减缓

Application of lime or gypsum is a common agricultural practice to ameliorate soils with low pH which prohibits crop production. Its integrated effect on soil properties in a red soil derived from Quaternary red clay in Southeast China is discussed in this paper. Application of gypsum in the topsoil without leaching raised soil pH and promoted the production of soil NH₄, but lime addition had a contrary effect. Generally, application of lime and/or gypsum has little effect on soil electrical properties. Gypsum had a little effect on soil exchange complex and its effect went down to 30 cm in depth. The effect of lime reached only to 5 cm below its application layer. With leaching, Ca transferred from top soil to subsoil and decreased exchangeable Al in subsoil. Gypsum application led to a sharp decrease in soil exchangeable Mg but had no effect on K.     

Sorghum growth,root responses,and soil‐solution aluminum and manganese on pH‐stratified sandy soil§

A stratified subsurface layer of acidic soil can develop in minimally disturbed soil such as no‐till receiving injection of N fertilizer (e.g., anhydrous ammonia). The objective of this study was to evaluate the effectiveness of subsurface band treatments in alleviating soluble Al³⁺ and Mn²⁺ toxicities on sorghum growth. Soil columns 40 cm in length were packed with soil (Valentine fine sand mixed mesic Typic Ustipsamment and Thurman loamy sand mixed Mesic Udorhentic Haplustoll) with treatments applied at the 10–18 cm depth to mimic soil pH stratification. The treatments at this depth were: (1) entire layer at soil pH of 3.7; (2) band of soil 6 cm wide at pH of 5.8 with the rest of the soil at pH 3.7; (3) band of soil 6 cm wide at pH of 6.3 with the rest of the soil at pH 3.7; and (4) entire layer at soil pH of 5.8. The soil above and below the 10–18 cm depth was at pH 5.8. Sorghum (Sorghum bicolor L. Moench) was grown in the soil columns under a controlled environment for 6 weeks. High concentration of Al in soil solution was found in soil at soil pH 3.7 which was overcome by either banding to pH 5.8, 6.3, or having the soil layer at pH 5.8. Treatment with pH of 5.8 throughout the soil 10–18 cm depth produced significantly greater top growth, although all other pH or liming strategies performed better than the soil pH 3.7 treatment. The banded treatments at pH 5.8 and 6.3 allowed roots to grow below the 10–18 cm layer of soil, but root growth was still significantly less than in the soil where the entire soil treatment layer was at pH 5.8. The increase in biomass yield with soil pH of 5.8 in the entire treatment layer was higher compared to band treatment at pH 5.8; however, the lime requirement would be 3.4 times more with liming the entire layer compared to banding a portion of the soil to pH 5.8 and would thus be translated into a higher liming cost.     

The phosphorus status of German cropland—An inventory of top‐ and subsoils

Background : In search for more sustainable crop production, the subsoil has recently come into focus as considerable reservoir of nutrients and water. Aims : Dimensions of subsoil phosphorus (P) reserves are yet largely unknown but crucial for identifying regions suitable to include subsoil into sustainable management strategies. Methods : We analyzed stocks of total and plant‐available (calcium acetate lactate‐extractable) P in 96 representative soil profiles of German arable land down to 1 m depth. Results : We found that the German arable soils stored, on average, 8 t ha^?1 of total P, of which nearly 500 kg ha^?1 were readily plant‐available. Notably, one third of plant‐available P was located below the plow layer and one fifth even at depths below 0.5 m. The depth gradients of plant‐available P stocks were affected more by major reference soil group than by texture. Generally, Chernozem but also Anthrosol, Gleysol and Fluvisol exhibited the largest P stocks in German cropland. The contribution of plant‐available P to total P stocks was larger in sandy and extremely acidic (pH < 4.5) soils compared with more fine‐grained and slightly acidic to alkaline soils, possibly because fertilization compensated for overall lower total P stocks at these sites. Generally, the more P was stored in topsoils, the more P was stored also in subsoils. Conclusions : A hypothetical crop utilization of 10% from plant‐available P stocks and 0.1% from total P stocks from shallow subsoil could compensate for P fertilization by ca. 8 kg ha^?1, but the rate of plant‐available P replenishment in subsoil likely remains the crucial factor for the role of subsoil P stocks in crop nutrition. Generally, the large P reserves found in subsoil could act as an ‘insurance' system for crops.