Understanding relationships between sensor-based measurements Indicator measurements used to assess soil quality must and soil properties related to soil quality may help in developing sitebe responsive to management practices to observe changes specific management. The primary objective of this research was to that might either improve or impair the soil (Karlen examine whether sensor-based apparent soil electrical conductivity (EC a) could be used to predict soil properties for claypan soil. Soil et al., 1997; Wander and Bollero, 1999). Soil quality samples were obtained at three depths intervals (0-to 7.5-, 7.5-to indicators could be described into inherent soil proper-15-, and 15-to 30-cm depths) at 65 locations within a 4-ha area of an ties, those that change slowly over time (e.g., soil texture agricultural field located in north central Missouri in 2002. Samples and hydraulic characteristics), and dynamic soil properwere analyzed for numerous physical, chemical, and microbiological ties such as those that management can influence (e.g., properties that serve as soil quality indicators. The EC a measurements pH, soil water use from the tillage, and plant nutrient were also collected at the coring locations with an electromagnetic levels). A list of basic soil properties that meet many induction-based sensor. A combine equipped with a commercial yieldof the requirements for screening soil quality was develsensing, GPS based recording system was used to map corn (Zea oped by Doran and Parkin (1994). A framework for evalmays L.) and soybean [Glycine max (L.) Merr.] yields from 1993 to uating site-specific changes in soil quality was also devel-2002. At the deepest sampling depth, soil bulk density (D b), clay, silt, cation exchange capacity (CEC), and Bray-1 P were the most oped by Karlen and Stott (1994), where high-quality significantly correlated (r Ͼ 0.55) with EC a. Soil properties were soil was defined as one that accommodates water entry, regressed against EC a , and R 2 values were often improved using a retains and supplies water to plants, resists degradation, quadratic term of EC a , especially at the 0-to 7.5-cm depth. Selected and supports plant growth. regression models were validated with an independent soil sample An evaluation of how various management practices data set (n ϭ 20). Soil properties were similar between measured and affect soil quality in claypan soils is important because predicted. Some soil properties (e.g., clay and CEC) and EC a that these soils are highly sensitive to soil degradation from were positively correlated to yield in years with average or greater processes such as runoff and erosion (Nikiforoff and than average cumulative July to August precipitation (Ͼ15 cm) were Drosdoff, 1943; Kitchen et al., 1998). The central claynegatively correlated to yield for years with less than average precipipan soil region occupies about 4 million ha in Missouri tation (Ͻ15 cm). Our results suggest that sensor-based EC a can be a quick and economical way of estimating some claypan s...

Spatial variability in soil properties has long been observed within uniformly managed fields. Understanding the spatial characteristics of soil properties would be helpful in understanding soil-landscape relationships and in the development of site-specific management. The primary objective of this research was to quantify the spatial characteristics of claypan soil properties for a 4-ha agricultural field located in north-central Missouri. Soil samples were collected in 2002 at three depths (0-7.5, 7.5-15, and 15-30 cm) on a 30-m grid. Samples were analyzed for physical, chemical, and microbiological properties. Handheld and mobile apparent soil-profile electrical conductivity (EC a ) values were also obtained. Spatial dependence was not identified for many properties. Yet, at a separation distance of |40 m, clay and silt content, cation exchange capacity, and Bray-1 P were spatially autocorrelated for the 15-to 30-cm depth. Soil EC a showed a similar spatial autocorrelation. Spatial variations in most soil properties were better estimated by cross-semivariance analysis with EC a as a secondary variable than by simple semivariance analysis. Clay content was lowest and mostly homogeneous at the 0-to 7.5-cm depth (mean 5 170 g kg 21 , SD 5 2.0), and highest and most variable at the 15-to 30-cm depth (mean 5 410 g kg 21 , SD 5 15.8). Thus, the spatial characteristics of soil texture and related soil properties varied greatly by depth and landscape position, probably the result of an uneven distribution of topsoil caused by tillage-accelerated water erosion. We conclude that characterizing the variation in the depth of the claypan horizon is a helpful step in describing other properties for these soils.

Crop management has the potential to either enhance or degrade soil quality, which in turn impacts on crop production and the environment. Few studies have investigated how crop management affects soil quality over different landscape positions. The objective of the present study was to investigate how 12 years of annual cropping system (ACS) and conservation reserve program (CRP) practices impacted soil quality indicators at summit, backslope and footslope landscape positions of a claypan soil in north-central Missouri. Claypan soils are particularly poorly drained because of a restrictive high-clay subsoil layer and are vulnerable to high water erosion. Three replicates of four management systems were established in 1991 in a randomized complete block design, with landscape position as a split-block treatment. The management systems were investigated: (1) annual cropping system 1 (ACS1) was a mulch tillage (typically ≥ 30% of soil covered with residue after tillage operations) corn (Zea mays L.)-soybean (Glycine max (L.) Merr.) rotation system, (2) annual cropping system 2 (ACS2) was a no-till corn-soybean rotation system, (3) annual cropping system 3 (ACS3) was a no-till corn-soybean-wheat (Triticum aestivum L.) rotation system, with a cover crop following wheat, (4) CRP was a continuous cool-season grass and legume system. In 2002, soil cores (at depths of 0-7.5, 7.5-15 and 15-30 cm) were collected by landscape position and analyzed for physical, chemical and biological soil quality properties. No interactions were observed between landscape and crop management. Relative to management effects, soil organic carbon (SOC) significantly increased with 12 years of CRP management, but not with the other management systems. At the 0-7.5-cm soil depth in the CRP system, SOC increased over this period by 33% and soil total nitrogen storage increased by 34%. Soil aggregate stability was approximately 40% higher in the no-till management systems (ACS2 and ACS3) than in the tilled system (ACS1). Soil aggregation under CRP management was more than double that of the three grain-cropping systems. Soil bulk density at the shallow sampling depth was greater in ACS3 than in ACS1 and ACS2. In contrast to studies on other soil types, these results indicate only minor changes to claypan soil quality after 12 years of no-till management. The landscape had minor effects on the soil properties. Of note, SOC was significantly lower in the 7.5-15-cm soil depth at the footslope compared with the other landscape positions. We attribute this to wetter and more humid conditions at this position and extended periods of high microbial activity and SOC mineralization. We conclude that claypan soils degraded by historical cropping practices will benefit most from the adoption of CRP or CRP-like management.

Increasing rice grain yield is critical for feeding rapid increasing of Asian population. However, global warming effect may be negative for sustainable rice production. Therefore it is essential to develop technologies not only for increasing grain yield but also for reducing global warming effect. Biochar, which is carbonized biomass, has a great potential of carbon sequestration and soil quality improvement, which can contribute grain yield increasing. In this study, rice yield responses to biochar application on the rice cropping system were evaluated with field experiments under different water management practices at the research farm of the University of Missouri-Columbia Delta Research Center, Portageville, MO. Biochar (i.e., 4 Mg ha -1 ) was produced using field scale pyrolyzer and incorporated into the field 4 months prior to planting. Rice was grown under three different water management practices. Result showed that no significant yield difference was found in the biochar application plots compared to rice hull and control plots from the 2 years field study at the very fertile soil. However, rainfed management results in severe reduction of yield. Research concludes that the biochar application does not significantly influence on rice yield increasing especially for very fertile soils.

Application of biochar to soils is proposed as a significant, long-term, sink for atmospheric carbon dioxide in terrestrial ecosystems. In addition to reducing emissions and increasing the sequestration of carbon, production of biochar and its application to soils will contribute improve soil quality and crop productivity. Objectives were i) to evaluate biochar productivity from crop residues using a low-cost field scale mobile pyrolyzer and ii) to evaluate characteristics of feedstocks and biochars from locally collected crop residues. Pyrolysis experiments were performed in a reactor operated at 400-500°C for 3-4 hours using biomass samples of post-harvest residues of corn (Zea mays L.), cotton (Gossypium spp.), rice (Oryza sativa L.), sorghum (Sorghum bicolor L.) and wheat (Triticum aestivum L.). Feedstocks differed, but average conversion to biochar was 23%. Carbon content of biomass feedstock and biochar samples were 445 g kg-1 and 597 g kg-1 , respectively. Total carbon content of biochar samples was 34% higher than its feedstock samples. Significant increases were found in P, K, Ca, Mg, and micro-nutrients contents between feedstock and biochar samples. Biochar from corn stems and rice hulls can sequester by 60% and 49% of the initial carbon input into biochar respectively when biochar is incorporated into the soils. Pyrolysis conversion of corn and rice residues sequestered significant amounts of carbon as biochar which has further environmental and production benefits when applied to soils. Field experiment with crop residue biochar will be investigated the stability of biochars to show long-term carbon sequestration and environmental influences to the cropping systems.