Landscape position moderates how ant nests affect hydrology and soil chemistry across a Chihuahuan Desert watershed

Ants moderate the supply of critical resources such as water and nutrients in desert environments by changing the physical arrangement of soils during nest construction. We measured water infiltration and soil physical and chemical properties on and off the nests of two ant species (Pogonomyrmex rugosus, Aphaenogaster cockerelli) across five sites at differing landscape positions within a Chihuahuan Desert watershed. Our aim was to test whether the effects of these long-lived ant nests on water infiltration and soil chemistry varied between ant species or across sites within a watershed. Water flow was generally slowest at the site with the highest silt and clay contents, and fastest at the site with sandy soils. Flow was generally greater through ant nest soils than adjacent non-nest soils, and we attribute this to increases in macropores in the nests. However, the effects of both ant nests and species varied among sites. Despite wide variation in soil chemical properties across all sites, ant nests had a consistent effect on soil chemical properties, with higher levels of carbon, nitrogen, sulphur, phosphorus and electrical conductivity on nests compared with non-nest soils. Our results demonstrate that while we can generalise about the effects of ant nests on water flow and nutrient levels, differences in soil type, nest density and ant species across sites are likely to moderate these effects.     

甘肃省主要农业区土壤对磷的吸附与解吸特性

实测的等温吸附曲线与常用的Freundlich、Langmuir及Temkin的吸附模式均很吻合,全部相关系数均达极显着水平。由吸附曲线得到的土壤对磷的吸附特性值(k·x_m)差异较大,东部地区较西部高,覆盖黑垆土>黄绵土>黑麻土>灌漠土。影响土壤吸磷的因素主要是土壤有机质含量和阳离子代换量(CEC),有机质含量越高,土壤对磷的吸附结合能越小,而吸磷量增加;土壤吸附磷的解吸曲线不同层次与土壤吸附磷的结合方式不同有关。水溶性磷加入土壤后,首先形成二钙磷,其次是Al-P,再次是八钙磷,并逐渐形成更难溶的磷酸盐形式。     

Tillage and drainage impact on soil quality: II. Tensile strength of aggregates, moisture retention and water infiltration

Tillage-induced changes in soil quality are important to understanding soil strength and water retention and transmission properties. Thus, this study was conducted to assess the effects of two tillage systems under un-drained and drained conditions on tensile strength (TS) of 5–8 mm aggregates, soil water characteristics (SWC), plant available water (PAW), and the water infiltration rate (i). Soil properties were determined mainly in the surface (0–10 cm) layer on a Crosby (fine, mixed, mesic, Aeric Ochraqualf) silt loam soil at the Waterman Farm of the Ohio State University, Columbus, OH on a 14-year-old field study. Effect of two tillage treatments comprising no-tillage (NT) and conventional tillage (CT) were studied for two levels of drainage: un-drained (UD) and tile drained (D). The TS for 0–10 cm depth was significantly (P ≤ 0.01) affected by tillage and drainage treatments, and was higher in CT than NT by 61% in UD and by 48% in D soil. In comparison, TS increased by 13% in NT and 4% in CT in D compared with the UD treatments. Soil organic carbon (SOC) in 0–10 cm depth of NT–UD treatment was 23% higher than CT–UD treatment and 38% more than NT–D treatments. Tillage and drainage impact on SWC was non-significant at 0 kPa suction, but significant (P ≤ 0.1) at −3, −6, −10, −30, −100 and −300 kPa suctions indicating that water was retained more in NT–UD than CT–UD soil. The PAW was significantly influenced by drainage (P ≤ 0.01) but not by tillage treatments. Yet, there existed a general trend of about 8% more PAW in NT–UD than CT–UD treatments. In contrast, PAW was 48% more in soil from NT–UD than NT–D treatments. PAW increased with increase in the SOC concentration (R² = 0.89; P ≤ 0.01). There were also differences in soil water sorptivity (S), and equilibrium infiltration rate (i_c) in NT–UD compared with CT–UD treatments. A positive and significant correlation (r = 0.57, P ≤ 0.05) occurred between i_c and SOC concentration. The value of S was more in NT–UD by 70% than CT–UD, and 46% in NT–D than CT–D. Similarly, the i_c was more in NT than CT by 119% in UD compared with 82% in D soil. The value of A in NT was higher than that in CT by 39% and 12% in UD and D treatments, respectively. The mean cumulative infiltration (I) in 3 h was 71.4 cm in NT versus 44.0 cm in CT in UD compared with 62.1 cm in NT and 48.4 cm in CT for the D treatment. The I was positively and significantly correlated with SOC concentration (r = 0.32, n = 12, P ≤ 0.1) indicating improvement of I with increase in SOC concentration. Results of this study suggest that conversion from CT to NT management system may reduce the risk of surface runoff, increase soil aggregation, and improve soil hydrological properties.     

Soil water relations of a Nigerian typic haplustult amended with fresh and burnt rice-mill wastes

The soils in the Abakaliki agro-ecological region of southeastern Nigeria are plagued with characteristics that impede optimal soil water conditions. Four rates (12.5, 25.0, 37.5 and 50.0 Mg ha⁻¹) of fresh (FW) and burnt (BW) rice-mill wastes were incorporated in a typic haplustult planted with maize (Zea mays L.) to improve the immediate and long-term water conditions of the soil. Results showed that significant changes in bulk density and total porosity occurred at the application rates of 25.0 and 50.0 Mg ha⁻¹ in the FW and BW amendments, respectively. At an application rate of 50.0 Mg ha⁻¹, the permanent wilting point water content (18.0%) in the FW amendment was significantly higher than the BW amendment. Similarly, the FW amendment at the same application rate resulted in the infiltration rates (i) of 2250 and 2181 mm h⁻¹ in the first and second seasons, respectively. These figures are significant improvements relative to the BW amendments and the control. Percent organic carbon (OC), dry aggregate size >0.5 mm and water stable aggregates (WSA) > 0.5 mm accounted for 43% and 77%, respectively of the improved infiltration. Sorptivity and A parameter of Philip's equation increased significantly with increasing rate of the FW amendment. Appropriate moisture conservation techniques are required to accelerate the rate of decomposition of the FW amendment in order to enhance its contribution to soil water retention.     

Effect of straw and plastic film management under contrasting tillage practices on the physical properties of an erodible loess soil

The current cropping system of excessive tillage and stubble removal in the northwestern Loess Plateau of China is clearly unsustainable. A better understanding of tillage and surface cover management on surface soil structure is vital for the development of effective soil conservation practices in the long term. Changes in surface soil structure and hydraulic properties were measured after 4 years of straw and plastic film management under contrasting tillage practices (no tillage vs. conventional tillage) in a silt loam soil (Los Orthic Entisol) which had been under conventional management for hundred of years in the northwestern Loess Plateau, China. Surface soil (0–10 cm) under no tillage with straw cover had the highest water stability of macro-aggregates (>250 μm) and the highest saturated hydraulic conductivity. Compared with straw cover, plastic film cover did not change macro-aggregate stability and the soil had the lowest saturated hydraulic conductivity (K_sat) but the highest % <50 μm soil particles. Significant correlation was found between water stable macro-aggregates and soil organic carbon content, indication the importance of the latter on soil structural development. No tillage on its own (without straw cover) was not sufficient to improve structural stability probably due to lack of organic carbon input. While use of plastic film cover might lead to short term yield increases, results indicated that it did little to improve soil physical fertility. On the other hand, no tillage with straw cover management should lead to long-term improvement of physical quality of this structurally fragile soil.     

Geostatistical analysis of sorptivity for a soil under tilled and no-tilled conditions

The properties of soils, even in short distances differ from point to point. These spatial variabilities may be described by geostatistics. This method determines the spatial structure of a specified variable. In this study, we measured the sorptivity of soil in field under tilled and no-tilled conditions with different sampling distances by using a simple method and performed the geostatistical analysis on the obtained data. The measurements were done on the corners of a regular network having dimensions of 5 m × 5 m in a tilled and no-tilled soil, and 0.5 m × 0.5 m in the same tilled soil. The results revealed that sorptivity had spatial structure in a tilled soil with 0.5 m × 0.5 m grid distances and no spatial structure occured in 5 m × 5 m distances, so it was believed that sorptivity is a structural variable only for short distance. The range of variogram was between 3.09 and 3.42 m for the sorptivity with 0.5 m × 0.5 m grids. The spherical model was the best-fitted theoretical variogram. In addition to the simple method for sorptivity measurement, we measured the sorptivity using double rings, which is known as Talsma method. Statistical tests showed a significant and non-significant difference between the two methods in 5 m × 5 m and 0.5 m × 0.5 m grids, respectively. In the simple method for sorptivity measurement, a ring with 10 cm height, 10 cm diameter, and about 2 cm depth of water was applied, but the rings used in the Talsma method were about three to four times larger. Therefore, it is concluded that for short distances, the sorptivity of simple method is in accordance with that obtained in Talsma method. The kriging method was used to estimate the presumed unknown values of sorptivity in some locations in the 0.5 m × 0.5 m grid distances. Results revealed that kriging method is capable enough to estimate the sorptivity if the variable has a spatial structure.