Americas and Oceania Group - International Plant Nutrition Institute

Improving the Method and Classification System for Evaluating Soil Available Potassium and Plant Potassium Status for
Rice and Winter Wheat in Nanjing
Project Leader: Huoyan Wang, Chinese Academy of Science Nanjing Institute of Soil, Nanjing, Jiangsu.
E-mail: hywang@issas.ac.cn
Project Cooperator: Xiaoqin Chen
Scarce and imbalanced application of K in China has resulted in a widespread exhaustion of K reserves
in cropland soils during recent decades. The most common soil K fertility index used is soil available K,
measured using the 1 mol/L ammonium acetate (NH 4 OAc) method. However, this method was only suitable
for evaluating K availability in soils of the same type or with similar K buffering capacity, but not in soils
with variable K buffering capacity, or in soils where the non-exchangeable K contribution to plant K uptake
varies. So, establishing a better method to accurately determine plant available K in various soils and the
precise diagnostic indexes of plant K and a stable uniform fertilizer recommendation index are important
for improving K utilization efficiency. The Nanjing Institute of Soil Science, Chinese Academy of Sciences,
conducted in 2011 a rice pot culture experiment with 12 soils differing in K fertility and K buffering capacity.
During the whole growing period, different tissues of rice plants were sampled according to the growing
stages. The tissue K content was measured and compared among different organs and different growth stages.
The relationship between tissue K content and soil K availability indicated by various methods was analyzed
to find which method would best define the plant available K in the soil.
Result showed that the first leaf (counting from top) K content at tillering stage, the third leaf K at
elongation stage, and the K content of the third leaf including the sheath at full heading stage could be used
as diagnostic indices of rice K nutrition. Potassium contents of 3.46, 1.77, and 1.00% in the diagnostic organs
at the three growing stages could be used as the indices of rice K supply status. Both sodium tetraphenyl
boron (NaBPh 4 ) method (0.2 mol/L, 30 min) and cold HNO 3 extraction method (0.5mol/L, 8 h) are good for
evaluating rice soil K availability. Based on the mathematical function obtained via the relationship between
soil available K content and relative yield of rice, taking relative yield of 90% as the critical point, the critical
values for soil available K were 330 and 144 mg/kg for NaBPh 4 and HNO 3 methods, respectively. Nanjing-12
Fertilization Recommendation Technique for Vegetable Greenhouse in Shanghai Suburbs
Project Leader: Yao Zheng, Shanghai Academy of Agricultural Science Resources and Environment Institute, Shanghai,
Shanghai. E-mail: zyao@saas.sh.cn
Project Cooperator: Song Ke, songke115@yahoo.cn
Protected (greenhouse) vegetable land has developed quickly in recent year in Shanghai suburbs to increase
farm productivity. According to 2010 statistics, including 9 districts and Chongming county and Guangming
Food Corporation, Shanghai already has more than 13,501 ha of horticultural facilities (greenhouse).
However, many problems such as secondary salinization, acidification in vegetable greenhouse soil have
become more and more serious. About 30% of the greenhouses soils have suffered stress of secondary
salinization. Soil secondary salinization is the main reason for limiting vegetable production in greenhouse
in Shanghai suburbs. In order to study the influence of soil salinity on vegetable, greenhouse pot experiments
were conducted in 2011 by the Soil and Fertilizer Institute, Shanghai academy of agricultural Sciences.
Hoagland nutrition liquid was used in these experiments as nutrient resource.
Results indicated that excessive fertilization resulted in salinization, which inhibited and harmed the growth
of the vegetables. The damage of soil secondary salinization to vegetable mainly occurs at the seedling stage
with germination rate and/or survival rate of seedling. Under normal circumstances, the threshold limit at
which soil salinity can harm vegetable seedling was found out to be 3.0 g/kg. Vegetable seedlings would be
seriously harmed when the content of soil salinity reached 6.0 g/kg. Shanghai-09
Environmental Factors Affecting Uptake and Utilization of Nitrogen and Phosphorus by Vegetable Crops
Project Leader: Lin Xian-yong Zhejiang University Resource and Environment College Kaixuan Road 268, Hangzhou,
Zhejiang. E-mail: xylin@zju.edu.cn, linxy@hzcnc.com
Project Cooperators: Zhang Yong-song and Zhang Qichun
The intensive vegetable cultivation using high fertilizer input were selected to study the effects of
environmental factors on transformation, uptake, and utilization of N and P in soils. The objective of the
study was to provide a theoretical basis and technical support for improving fertilizer use efficiency. Soil
water contents in the incubation experiments were kept constant in this study. Two greenhouse vegetable soils
were used. The soils had different soil N mineralization microbial communities—difference in community
76 IPNI Interpretive Summaries