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The Mission of Soil Science in a Changing World

The soil is a vital, complex, and labile medium. To manage it effectively and sustainably, we must strive to understand its attributes, functions, and environmental interactions. Toward this holistic end, we need to overcome traditional disciplinary and institutional barriers so as to promote interdisciplinary cooperation among teams of scientists with different but mutually complementary specialities. Herein, we provide an historical and cultural review of the evolving relationship between humanity and the soil.

A Historical Summary of Alabama's Old Rotation (circa 1896): The World's Oldest, Continuous Cotton Experiment.

After more than 110 yr, the Old Rotation experiment on the campus of Auburn University in Alabama continues to document the long-term effects of crop rotation and winter legume cover crops on sustainable cotton (Gossypium hirsutum L.) production in the southeastern United States. Long-term yields indicate that winter legumes are as effective as fertilizer N in producing maximum cotton yields and increasing soil organic carbon (SOC). Higher SOC resulted in higher crop yields. However, rotating cotton with corn (Zea mays L.) in a 2-yr rotation or with corn, winter wheat (Triticum aestivum L.), and soybean [Glycine max. (L.) Merr.] in a 3-yr rotation produced little long-term cotton yield advantage beyond that associated with SOC. Cotton yields without winter legumes nor fertilizer N are only slightly higher than they were 110 yr ago. Nonirrigated corn grain yields in rotation with cotton are typically low for central Alabama and appear limited by N. Yields of all crops on the Old Rotation increased with increasing rates of P and K through the 1950s. Since adoption of in-row subsoiling, high-residue, conservation tillage, and genetically modified cultivars in 1997, all crops have produced their highest, nonirrigated, recorded yields since the experiment began: 1910 kg cotton lint ha-1 in 2006, 14.8 Mg corn grain ha-1 in 1999, 6.34 Mg wheat ha-1 in 2001, and 4.50 Mg soybean ha-1 in 2004.

Decadal Changes in Potassium, Calcium, and Magnesium in a Deciduous Forest Soil

Decadal changes in soil exchangeable K+, Ca2+, and Mg2+ concentrations and contents from 1972 to 2004 in eight intensively monitored plots on Walker Branch Watershed were compared with estimates of increments or decrements in vegetation and detritus. The results from these eight plots compared favorably with those from a more extensive set from 24 soil sampling plots sampled in 1972 and 2004. Increases in exchangeable K+ were noted between 1972 and 1982, but few changes were noted between 1982 and 2004 despite significant increments in vegetation and detritus and significant potential losses by leaching. Total K contents of soils in the 0- to 60-cm sampling depth were very large and a slight amount of weathering could have replenished the K+ lost from exchanges sites. With one notable exception, exchangeable Ca2+ and Mg2+ concentrations and contents decreased continuously during the sampling period. Decreases in exchangeable Ca2+ could be attributed mostly to increments in biomass and detritus, whereas decreases in exchangeable Mg2+ could not and were attributed to leaching. The major exception to these patterns was in the case of exchangeable Ca2+, where significant increases were noted in one plot and attributed to Ca release from the decomposition of Ca-rich coarse woody debris from oak (Quercus spp.) mortality. With minor exceptions, soils and changes in soils among the eight intensively sampled core plots were similar to those in a more extensive set of plots distributed across the watershed. This study shows that averaging among plots can mask significant and important spatial patterns in soil change that must be taken into account in assessing long-term trends.

Yield Response of Potato to NPKS Fertilizers in old Brahmuputra Floodplain Soil

The experiment was conducted at Multilocation Testing Site (MLT) Kishoregonj sadar in an irrigated medium high land under Old Brahmaputra Floodplain AZE 9 during Rabi seasons of 2003-2004 and 2005-2006. The objectives were to evaluate the response of potato to NPKS fertilizers and to find out the optimum dose of nutrients for maximum tuber yield of potato. Fourteen treatments were tested formulating from 4 levels each of N, P, K, and S. Significantly higher yield of tuber was obtained from T3 (N120, P30, K90 and S20 kg/ha). Regression analysis showed that optimum rate of N, P, K and S was 121, 33, 104 and 18 kg/ha, respectively for the maximum tuber yield. The optimum economic dose of N, P, K and S were appeared as 120, 30, 90 and 20 kg/ha, respectively. Considering yield, economics, regression analysis and nutrient status of soil at the rate of N120, P30, K90 and S20 kg/ha was found suitable for potato production under AEZ 9.

Effect of Long-Term Application of Chemical Fertilizers on Microbial Biomass and Functional Diversity of a Black Soil

An experiment with seven N, P, K-fertilizer treatments, i.e., control (no fertilizer), NP, NK, PK, NPK, NP2K, and NPK2 where P2 and K2 indicate double amounts of P and K fertilizers respectively, was conducted to examine the effect of long-term continuous application of chemical fertilizers on microbial biomass and functional diversity of a black soil (Udoll in the USDA Soil Taxonomy) in Northeast China. The soil microbial biomass C ranged between 94 and 145 mg kg-1, with the NK treatment showing a lower biomass; the functional diversity of soil microbial community ranged from 4.13 to 4.25, with an increasing tendency from control to double-fertilizer treatments, and to triple-fertilizer treatments. The soil microbial biomass, and the microbial functional diversity and evenness did not show any significant differences among the different fertilizer treatments including control, suggesting that the long-term application of chemical fertilization would not result in significant changes in the microbial characteristics of the black soil.

Effects of Low Potassium Stress on Mineral Nutrient Absorption and Phytohormone Contents of Rice Seedling

Two low potassium tolerant rice (Oryza sativa L.) genotypes, N18 and N19, and their recipient, N27 (control) were used to investigate the effects of low potassium stress on mineral nutrient absorption and phytohormone contents of leaves of rice at the seedling stage using a solution cultivation experiment. The results show that potassium uptake efficiency, potassium utilization efficiency and potassium translocation rate of the 3 genotypes were decreased under the low potassium stress. The decreased values of N18 and N19 are less than those of N27. Furthermore,under low potassium stress, absorption abilities and translocation abilities of Na, P, Mg, Fe and Ca of N18 and N19are stronger than those of N27. Under low potassium stress, IAA, GA1 and ZR contents of leaves for all genotypes are decreased, and as well as the ratios of IAA/ABA, ZR/ABA and GA1/ABA.The reduced amounts of IAA, GA1 and ZR of N18 and N19 are less than those of N27. While ABA contents are increased, the increased amounts of N18and N19 are less than that of N27. These results indicate that the characteristics of rice resistance to low potassium stress are related to their abilities to absorb mineral nutrients and the contents of phytohormones.

Spatial Variability of Soil Available N, P and K and Influencing Factors

Studies on the spatial variability characteristic of soil available nutrient contents in county scale could provide a guidance for improving agricultural planning. Geostatistics combined with GIS were used for the analysis of the spatial variability characteristics of soil available nitrogen (AN), available phosphorus (AP) and available potassium (AK) and their influencing factors in Shuangliu county in Sichuan province. The results indicated: 1) AN and AK contents were strongly and spatially dependent, the range of spatial dependence was 77840 m and 75482 m. Structural factors were the main factors which affected the spatial variability of AN and AK contents. AP content had moderate spatial dependence, the range of spatial dependence was 25590 m, and the spatial variability was caused by structural factors and random factors. 2) AN content was decreased from north to south, AP contents was decreased from northeast to southwest and southeast to northwest, whereas AK contents was decreased from southeast to northwest. 3) AN content was significantly different among different soil types or geography; AP content was significantly different among different soil parent materials whereas significantly different among different geomorphologic conditions; AK content was significantly different among different soil parent materials. The fertilizer application rate at the regions with high soil available N，P and K contents were obviously higher than regions with low soil available nutrient contents.

Establishing Phosphorus and Potassium Fertilization Recommendation Index Based on the "3414" Field Experiments

Recently, numerous field experiments are conducted in national soil testing and fertilization recommendation project, however, how to use these experimental data to establish fertilization recommendation index is urgently needed. Taking the winter wheat "3414" experiments in Shandong Province as an example, the process of establishing fertilization recommendation index was investigated and discussed. Soil Olsen-P and NH4OAc-K were classified as low (<75% relative yield), medium (75%-90% relative yield), high (90%-95% relative yield) and very high (>95% relative yield) based on the relative yields. Fertilizer recommended rates were simulated by the models of three-factor or one-factor for each "3414" field experiment. The results indicate that phosphorus fertilizer rates (P2O5) are 100-130, 80-100, 60-80, and 0 kg/ha when soil fertility are classified as low, medium, high and very high (Olsen-P<10, 10-30, 30-50 and >50 mg/kg), respectively, while potassium fertilizer rates (K2O) are 120-150,100-120, 60-80, and 0 kg/ha (NH4OAc-K <50, 50-100, 100-140 and >140mg/kg). Therefore, establishing fertilization recommendation index based on "3414" field experimental data is practicable.

Absorption and Distribution of Nitrogen, Phosphorus and Potassium in Onion

The growing characteristics of onion planted in autumn and its absorption and distribution rule on nitrogen, phosphorus and potassium were studied. The results showed that dry matter accumulation in onion at the seedling stage was very slow and absorption speed of the nitrogen, phosphorus and potassium was very low, which only accounted for about 4% of the whole nutrient. At plant vigorous growth stage, the uptake rates of N, P2O5, K2O were 22.03, 8.60 and 15.65 mg/(plant·d), accounted for 92.74%, 91.01%, 71.79% of nutrient uptake during the whole growing stages. At the bulb expanding stage, the uptake rate of N and P2O5 decreased rapidly, but the rate of K2O was still kept at 7.23 mg/(plant·d). The proportion of onion absorption to N, P2O5 and K2O was 1:0.40:0.92 taking the whole growing stages into consideration. The absorption rate of phosphorus and potassium increased with onion growing, and reached 1:0.92:9.04 at the bulb expanding stage. Nitrogen, phosphorus and potassium were mainly distributed in leaf at the seedling stage, in bulb and leaf at the plant vigorous growth stage and in bulb at the bulb expanding stage, with distribution rate being 75.88%, 87.7% and 71.81%, respectively. The demands for N, P2O5 and K2O were about 2.93, 1.16 and 2.69 kg for every 1000 kg bulb product, respectively.

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March 2009

English