Chunyu Song

Soil Organic Carbon Dynamics in Black Soils of China Under Different Agricultural Management Systems

Cultivation can reduce soil organic carbon (SOC) content and lead to soil deterioration, but some agricultural management systems may increase SOC content and soil productivity. This research examined the SOC dynamics during a 50-year cultivation and how long-term agricultural management practices influenced SOC content in a typical black soil (Mollisol) region of P.R. China. The experiments selected four areas with different cultivation periods: uncultivated, five years, fourteen years, and fifty years. In addition, four long-term agricultural managements were initiated in 1992: conventional wheat–soybean rotation, wheat–sweet clover rotation, wheat–soybean rotation with addition of pig manure, and wheat–soybean rotation with addition of wheat straw. The SOC content declined rapidly at early years of cultivation and gradually afterwards. Wheat–soybean rotation with addition of wheat straw or pig manure resulted in a substantial increase in SOC content in 9 years. Thus, proper soil management can improve soil quality and health by increasing SOM content, and mitigate the greenhouse effect by sequestrating carbon dioxide from the atmosphere as indicated by the significant increase of organic carbon content in soil.

Impact of soil temperature and moisture on Mehlich-3 and Morgan soil test phosphorus.

Guidance for timing of sampling is seldom included in soil sampling protocols for agronomic phosphorus (P) fertilizer recommendations or P runoff risk assessment. Our objectives were to determine the influence of soil temperature and moisture content on (i) Mehlich-3 and Morgan soil test P (STP) levels and (ii) the accuracy of Mehlich-3 to Morgan STP conversion models used for nutrient management planning in New York. An incubation study with three silt loam, excessive P soils, three temperatures (5°C, 10°C, and 20°C), and three moisture contents (50%, 70%, and 90% of field capacity) showed that an increase in soil temperature from 10°C to 20°C decreased Morgan STP and showed inconsistent and small changes for Mehlich-3 STP. Both tests showed higher STP levels with soil moisture increase. The increase from 10°C to 20°C resulted in a decrease in the ratio of measured to predicted Morgan STP, reflecting a reduction in measured Morgan STP and an increase in predicted Morgan STP, mostly driven by an increase in Mehlich-3 calcium (Ca). The increase in moisture impacted the ratio of measured to predicted Morgan STP for one soil only (a pasture with native Ca content). Repeated sampling of 20 corn (Zea mays L.) fields in May, June, July, October, November, and the following April showed a large seasonal variability in STP results, with the most accurate predictions of Morgan STP from Mehlich-3 data upon sampling in October after corn harvest. We conclude that for the most accurate prediction of STP status, samples should be taken directly after corn harvest, especially when conversion equations that include pH and Mehlich-3 P, Ca, and aluminum are used.

Effect of soil temperature and moisture on soil test P with different extractants

Song, C., Zhang, X., Liu, X. and Chen, Y. 2012. Effect of soil temperature and moisture on soil test P with different extractants. Can. J. Soil Sci. 92: 537-542. Temperature and moisture are important factors affecting adsorption, transformation and the availability of soil phosphorus (P) to plants. The different temperatures and moisture contents at which soil is sampled might affect the results of soil test P (STP). In order to evaluate the effect of the temperature and moisture, as well as the fertilization level, on the results of soil test P, an incubation study involving three soil temperatures (5, 10, and 20°C), and three soil moisture contents (50, 70, 90% of field water-holding capacity) was conducted with Chinese Mollisols collected from four fertilization treatments in a long-term experiment in northeast China. Four soil P test methods, Mehlich 3, Morgan, Olsen and Bray 1 were used to determine STP after a 42-d incubation. The effect of temperature and moisture on STP varied among soil P tests. Averaged across the four fertilization treatments, the temperature had significant impact on STP, while the responses varied among soil P test methods. Mehlich 3, Morgan and Bray 1 STP decreased and Olsen STP increased with increase in temperature. Effect of soil moisture was only significant for Mehlich 3 P and Olsen P. Soil temperature had greater impact on STP than soil moisture content. The responses of the Olsen method to temperature differed from the other three methods tested. The interaction between soil temperature and soil moisture on soil test P was only significant for Mehlich 3 P. Fertilization level does not affect the STP in as a clear pattern as the temperature and moisture varied for all four methods. Consistent soil sampling conditions, especially the soil temperature, appear to be the first step to achieve a reliable STP for any soil P test.