Americas and Oceania Group - International Plant Nutrition Institute

Study on High Efficiency Nutrient Use and Regulation of Soil Nutrient Dynamics for High Yields of Rice
Project Leader: Zheng Sheng-xian, Hunan Academy of Agricultural Science Soil and Fertilizer Institute, Changsha,
Hunan. E-mail: ylliao@ppi.caas.ac.cn
Project Cooperators: Nie Jun and Liao Yulin
Rice crop plays a crucial role in food production of China. Hunan is the largest rice production province in
China with an annual production of 29.1 M t. To study high efficiency nutrient use and regulate soil nutrient
dynamics for increasing rice yields, Hunan Institute of Soil and Fertilizer collected in 2011 a total of 24
samples from eight main double-rice production counties.
Results showed that the amounts of bacterium, fungi, and actinomycetes and the contents of soil microbial
biomass carbon (SMBC) and soil microbial biomass N (SMBN) in both high and medium productive paddy
soils did not differ significantly. Similarly, the observed trends in activities of urease, phosphatase, invertase,
dehydrogenase in both high and medium productive paddy soils showed no significant difference. Double rice
planting areas in Hunan, with a history of applying P fertilizer for the last 50 years at least leading to high soil
P levels, resulted in no significant differences in phosphatase activity in high, medium, and low productive
paddy soils. Correlation analysis showed that soil bacterium and actinomycetes had the best correlation with
soil organic carbon (SOC), total N (TN), total K, and available N (AN). Soil urease and invertase activities
had the best correlation with SOC, SMBC, SMBN, TN, AN. Most of the microbiological and biochemical
indicators did not differ significantly between high and medium productive paddy soils, but differed
significantly from the low productive paddy soil. Therefore, low productive paddy soil should get more
attention in terms of balanced application of organic manures and inorganic fertilizers. High productive paddy
soil in double-rice cropping regions of Hunan showed 48±12 g/kg of organic matter content, 2.7±0.7 g/kg of
TN, 40±14 mg/kg of available P, and 106±23 mg/kg of available K. Textures of high productive paddy soils
were generally loamy and sandy clay loam with weak K retention capacity. Therefore, since the available of
K content was not high in highly productive paddy soils, these soils would benefit from an application of K
fertilizer. Hunan-16
Effect of Rice Straw Return on Paddy Organic Content and Heavy Metal Availability
Project Leader: Zheng Sheng-xian, Hunan Academy of Agricultural Sciences Soil and Fertilizer Institute, Changsha,
Hunan. E-mail: shengxianzheng@foxmail.com
Project Cooperator: Nie Jun, junnie@foxmail.com
A long-term field experiment with early rice-late rice-winter fallow cropping system has been in place in
Wangcheng county since 1981. The treatments include CK (without fertilization), NP, NK, NPK, NK+Pig
manure (PM), NP+rice straw (RS), and NPK+RS.
Thirty-year average annual grain yield showed the following trend among treatments: control < NK <
NP < NK+PM < NP+RS < NPK < NPK+RS treatments. NPK treatment increased grain yield by 56.7 kg/
ha per year over NP treatment. A positive, linear correlation was observed between the soil organic matter
accumulation and the duration of the experiment in the NK treatment, while a negative, linear correlation was
observed in CK and NP treatments. There were significant differences in different treatments for soil organic
carbon (SOC), easily oxidizable organic carbon (EOC), microbial biomass carbon (MBC), light fraction
organic carbon (LFOC), humic acid organic carbon (HA-C) and fulvic acid organic carbon (HF-C) in the
plow layer of reddish paddy soils after 54 growing seasons. SOC, EOC, MBC, LFOC, HA-C and HF-C were
significantly higher in treatments with combined application of organic manures and inorganic fertilizers than
with the application of inorganic fertilizers (NP, NK and NPK) alone. The proportion of active organic C to
SOC was MBC