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A gronomy J our n al • Volume 10 0 , I s sue 3 • 2 0 0 8 517 ABSTRACT Th e improved soil N min -based N management is a promising approach to precision N management, which determines the optimum side-dress N rates based on N target values and measured soil nitrate N content in the root soil layer at diff erent growth stages. A total of 148 on-farm N-response experiments, in seven key summer maize (Zea mays L.) production regions of North China Plain (NCP) from 2003 to 2005, were conducted to evaluate the N min -based N management compared to traditional farmer's N practices. Th e recommended N rates based on the improved soil N min method were not signifi cantly diff erent ( ≤31 kg N ha -1 ) from those determined by yield response curves (n = 13). Th e average N rate determined with the soil N min method (157 kg N ha -1 ) was signifi cantly lower than farmer's practice (263 kg N ha -1 ), while maize grain yield was 0.4 Mg ha -1 higher than farmer's N practice (8.5 Mg ha -1 ) across all sites (n = 148). As a result, the improved soil N min -based N management signifi cantly increased net economic gains by $202 ha -1 , reduced residual nitrate N content and N losses by 44 kg N ha -1 and 65 kg N ha -1 , respectively, and improved recovery N effi ciency, agronomic N effi ciency and N partial factor productivity by 16%, 6 kg kg -1 and 36 kg kg -1 , respectively, compared with farmer's N practice. We conclude that the improved soil N min -based N management can be applied for summer maize production in NCP for improved N use effi ciency and reduced environmental contamination.

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Estimating indigenous nitrogen supply (INS) by measurement of crop N uptake in N omission plots for site-specific N management is not feasible on a routine basis because it involves destructive plant sampling and plant tissue analysis, which is time-consuming and expensive. The objective of this study was to determine the amount of INS and develop a method to estimate it using soil testing in the North China plain (NCP). On-farm experiments at 229 sites were conducted from 2003 to 2005 in seven key winter wheat (Triticum aestivum L.)/ summer maize (Zea mays L.) production regions of the NCP. The mean INS during the wheat-growing season was129 kg N ha -1 with a range from 62 to 212 kg N ha -1 , and it varied from 69 to 202 kg N ha -1 with a mean of 142 kg N ha -1 during the maizegrowing season. Considering all sites, the variability of INS was not simulated by initial soil N min or apparent N mineralization (N organic ) alone, while together they could explain about 38% and 60% of INS during the wheat and maize-growing seasons, respectively. During the wheat-growing season, mean N organic was 63 kg N ha -1 , and 59% and 33% of its variation could be explained by SOM in high-yielding regions (mean yield, 7.6 t ha -1 ) and low-yielding regions (mean yield, 5.3 t ha -1 ), respectively. Mean N organic during the maize-growing season was 109 kg N ha -1 , 22% of which could be explained by SOM across all sites. An average of 40% and 42% of INS variation could be explained by both SOM and initial soil N min content during the wheat and maize-growing seasons, respectively. We conclude that the accuracy of estimating crop N requirement for site-specific N management will be increased by using initial soil N min and SOM.

Nanospace materials can be used to influence and control chemical processes in their nanospaces, because they provide molecular reaction spaces with special properties. Layered materials, such as clay minerals and layered double hydroxides (LDHs), have been investigated extensively as nanospace materials, as they provide a stable two-dimensional nanospace for chemical processes. 1-17 A variety of molecules can be intercalated into the two-dimensional interlayer space of layered materials. The two-dimensional layer structure of layered materials is expandable with the size of the intercalated molecule. The intercalated molecule can form monolayers or bilayers in the interlayer space of layered materials independent of molecular size, due to the interaction between the layer plate and the molecule. Some novel chemical and physical properties can be obtained in two-dimensional layered molecular spaces that are different from the macroscopic space. 18-31 Thus, two-dimensional layered materials (11) Darder, M.; López-Blanco, M.; Aranda, P.; Leroux, F.; Ruiz-Hitzky, E. Chem. Mater. 2005, 17, 1969. (12) Frey, G. L.; Reynolds, K. J.; Friend, R. H.; Cohen, H.; Feldman, Y.