Effects of soil potassium levels on dry matter and nutrient accumulation and distribution in cotton

Background Potassium(K)is an essential nutrient for plant growth and development.However,plant fertilization ignoring the soil K level is very likely to cause excessive fertilizer use,and further arouse a series of side effects.This study investigated the response of cotton growth to different soil K levels and the uptake of major nutrients,aiming to evaluate the appropriate K supply level for cotton growth.Using a random block design with 6 soil K levels,we conducted 18 micro-zones field experiments over two continuous years.The soil available K concentration of each treatment was K1(99.77-100.90 mg·kg^(-1)),K2(110.90-111.26 mg·kg^(-1)),K3(123.48-128.88 mg·kg^(-1)),K4(140.13-145.10 mg·kg^(-1)),K5(154.43-155.38 mg·kg^(-1)),and K6(165.77-168.75 mg·kg^(-1)).Cotton nutrient contents,soil nutrient contents,accumulation and distribution of dry matter in cotton were determined,and the relationships between K content in soil and plants and dry matter accumulation were analyzed.Results The soil K content had a significantly positive relationship with dry matter and K accumulation in cotton plants.There were significant differences in dry matter accumulation,single-plant seed cotton yield,mineral nutrient uptake and the proportion of K accumulation in reproductive organs among different soil K levels.The results showed that there was significant difference between K4 and lower K level treatments(K1 and K2),but no significant difference between K4 and higher K level treatments(K5 and K6)in dry matter,single-plant seed cotton yield,or accumulation,distribution and seed cotton production efficiency of N,P and K.Conclusion The soil K level of K4 was able to provide sufficient K for cotton growth in our experiment.Therefore,when the soil K level reached 140.13 mg·kg^(-1),further increasing the soil K concentration no longer had a significant positive effect on cotton growth.

Diagnosis of Premature Senescence of Cotton Using SPAD Value

Field experiments were conducted in 2011 on an experimental farm at the Cotton Research Insti-tute, Chinese Academy of Agricultural Sciences, Anyang, China. We conducted experiments with a “SPAD-502” meter to quickly measure the relative value of chlorophyll content in the leaf blades of field cotton. Our goal was to seek a suitable leaf on a cotton plant to diagnose senescence status of crop plants at later stages of growth. We began by studying the dynamic change rule of the dis-tal-most four leaves of the cotton plant during the entire growth period with two early-maturing cultivars (CCRI 36, CCRI 50) and two mid-maturing cultivars (CCRI 41, SCRC 28). We also examined the effect of different nitrogen and potassium fertilizer rates on SPAD values of the leaves of SCRC 28. Our results suggest that SPAD values of the 1st distal stem leaves from two early cultivars can act as good indicators of senescence status in the plants, if they are measured between 10 d before the boll-opening stage and 10 d after boll opening stage. Differences of SPAD values of the 3rd distal stem leaves of two mid-maturing cultivars measured between about 15 d before the boll opening stage and 15 d after the boll opening stage can also be used to measure senescence status in these cotton cultivars. The conclusion can be used for cotton producer to manage N fertilizer better at later growth stage.