Objectives In order to provide theoretical basis for application of copper-based nutritional foliar fertilizers in cotton production, their effects on leaf photosynthetic characteristics, the total contents and accumulations of Cu, Zn and Fe in each organ, disease control efficiency, yield of cotton and enzyme activities of soil were investigated.

Methods A randomized block design field experiment was conducted for two consecutive years with cotton as tested material. Six treatments included spraying water (CK), Bordeaux Mixture (Cu 12.8%, BDM), Kocide 2000 (Cu 33.0%, KCD), copper-based nutritional foliar fertilizer (Cu 32.9%, Zn 0.8%, CF), iron-copper-based nutritional foliar fertilizer (Cu 32.9%, Fe 2.7%, CFFe), and zinc-boron-copper-based nutritional foliar fertilizer (Cu 32.9%, Zn 2.7%, B 2.9%, CFZnB). The chlorophyll contents in leaves were determined at different growth periods, and photosynthetic characteristics were determined at the peak bolling stage of cotton. Cotton plants were sampled at the beginning wadding stage, and then the whole plants were divided into four parts: root, stem, leaf and cotton boll, the contents and accumulations of total copper, zinc, and iron in each part were determined respectively, and soil enzyme activities were determined in each plot at the blossing and boll-forming stages. Disease indexes were statistically surveyed at the bud, blossom and boll-forming, and wadding stages.

Results 1) Spraying CFFe, CFZnB, CF and KCD significantly increased the chlorophyll contents, with the maximum increase of 13.3% in CFFe, followed by increase of 11.4% in CFZnB, compared to CK. Compared with CK, all the treatments increased the photosynthetic rate, stomatal conductance and transpiration rate, with the maximum increase of 26.4% in photosynthetic rate of CFFe, and followed by increase of 18.0% in CFZnB; significantly decreased intercellular CO₂ concentration in cotton leaves. 2) Spraying CFFe, CFZnB, CF, KCD and BDM significantly increased the total contents and accumulations of Cu in each organ of cotton, except the total copper contents of caudex in CFZnB; CFZnB and CFFe significantly increased the total contents and accumulations of Zn in each organ of cotton. CFFe, CFZnB and CF significantly increased the total contents and accumulations of Fe in each organ of cotton, except the total iron content of caudex in CF. 3) The spraying of CFFe, CFZnB, CF, KCD and BDM greatly reduced the disease index at the flowering, boll-forming and wadding stages of cotton as compared to CK, but there was no significant difference among the five treatments. Therefore, the effects of three kinds of copper based nutritional foliar fertilizer on cotton disease prevention can replace BDM and Kocide. 4) Soil urease activities of all foliar fertilizer traetments were not significantly different as compared to CK. All treatments significantly increased the catalase activities of soil as compared to BDM, and significantly increased the sucrase activities of soil as compared to CK. 5) The lint yields of cotton were improved by CFFe, CFZnB, CF and KCD in both 2013 and 2014, with the maximum increase of 12.3% in CFZnB, and followed by 8.8%‒10.2% in CFFe.

Conclusions Spraying copper-based, iron-copper-based and zinc-boron-copper-based nutritional foliar fertilizers could significantly increase the chlorophyll contents, photosynthetic rates in leaf and lint yields of cotton. Copper-based nutritional foliar fertilizer with trace elements can not only significantly increase cotton yield, but also has certain effects on cotton disease prevention and control. Zinc-boron-copper-based nutritional foliar fertilizer and iron-copper-based nutritional foliar fertilizer are recommended base on the experiments.