Synergistic effects of planting density and nitrogen fertilization on chlorophyll degradation and leaf senescence after silking in maize

Regulating planting density and nitrogen(N)fertilization could delay chlorophyll(Chl)degradation and leaf senescence in maize cultivars.This study measured changes in ear leaf green area(GLA_(ear)),Chl content,the activities of Chl a-degrading enzymes after silking,and the post-silking dry matter accumulation and grain yield under multiple planting densities and N fertilization rates.The dynamic change of GLA_(ear)after silking fitted to the logistic model,and the GLA_(ear) duration and the GLAearat 42 d after silking were affected mainly by the duration of the initial senescence period(T_(1))which was a key factor of the leaf senescence.The average chlorophyllase(CLH)activity was 8.3 times higher than pheophytinase activity and contributed most to the Chl content,indicating that CLH is a key enzyme for degrading Chl a in maize.Increasing density increased the CLH activity and decreased the Chl content,T1,GLAear,and GLA_(ear) duration.Under high density,appropriate N application reduced CLH activity,increased Chl content,prolonged T1,alleviated high-density-induced leaf senescence,and increased post-silking dry matter accumulation and grain yield.

Impacts of surfactant-based adjuvants on spray droplet size,drift distance,and deposition efficiency

The application of anti-drift nozzles,such as air-induction nozzles,is the most common recommendation for reducing spray drift;To reduce the risk of coarse droplets bouncing and rolling produced by anti-drift nozzles,various types of adjuvants were screened by comparing their atomization performance,surface tension and contact angle,in order to identify favourable adjuvants that are compatible with anti-drift nozzles.It was found from the study results that the addition of 50%neem crude oil emulsifiable concentrate(neem oil),isomeric alcohol ethoxylates and BYK-405 all significantly decreased distribution span(S)and the percentage of droplet size less than 150μm(ΦVol_(<150μm))values,but significantly promoted the median volume(D_(50))value.And the surface tension measurement results showed that all tested adjuvants significantly reduced the surface tension,while neem oil,FC4430 and silwetl-77 were observed with a most significant effects;Furthermore,all tested adjuvants except BYK-051N could also significantly decrease the contact angle,and the difference between neem oil,FC4430 and silwetl-77 was significant.Wind tunnel test results clearly demonstrated that the application of IDKA(a combination of air-induction nozzle IDK120-01 and neem oil)substantially decreased the drift deposition amount;In addition,the field experiments revealed that IDKA possessed a significantly improved deposition amount per unit area on canopy or bottom,leading to a more effective deposition.These results suggest that the use of IDK120-01 nozzle and neem oil can effectively reduce spray drift,lessen surface tension and enhance spreading.