Effects Of Different NO₃～-: NH₄～+ Ratios On Growth Of Pakchoi Under Low Light Intensity

Protected cultivation is a trend of modern agriculture. However in protectedcultivation, low light intensity probably becomes one of the limited factors for crop growth.Under natural light intensity proper NO₃^-:NH₄⁺ ratio could significantly improve growthand quality of crops. Then did the same effects occur to crops when nitrate and ammoniumwere mixed under low light in intensity?The pakchoi cultivar Shanghaiqing was selected for this experiment, and differentlight levels (natural light intensity, 50ï¼…natural light intensity and 25ï¼…natural lightintensity) and different NO₃^-:NH₄⁺ ratios (NO₃^-: NH₄⁺=100:0, 90:10, 85:15, 75:25) were setup. The effects of different NO₃^-: NH₄⁺ ratios on growth of pakchoi under low lightintensity were discussed, with the objective to study the interaction of light and nitrogenforms supplied, and give guide to solve light adversity in protected cultivation system.Results obtained were as followed.1, Growth of pakchoi was significantly inhibited when cultured under low lightintensity. 1) Biomass of pakchoi decreased by 63% and 76% when cultured under 50%and 25% nature light intensity; 2) photosynthetic rate, blade area and VLM of pakchoidecreased by 31%, 13% and 19% when cultured under 50% nature light intensity,respectively and decreased by 33%, 24% and 23%, when cultured under 25% nature lightintensity, respectively, compared with those cultured under nature light intensity; 3)content of nitrate in leaf blade of pakchoi cultured in pure nitrate solution were increasedby 106%, while content of soluble sugar, Vc and soluble protein were decreased by 7%,17% and 34% under 50% nature light intensity, compared with those grown under naturelight intensity; 4) Total Carbon accumulation of leaf, petiole and root decreased by 76.7%,84.5% and 79.4% while total nitrogen accumulation of those organs decreased by 71.2%,79.5% and 80.4%.2, Different NO₃^-:NH₄⁺ ratios significantly affected quality of pakchoi under low lightintensity. 1) Yield and soluble protein content increased, then decreased with decreasing of NO₃^-:NH₄⁺ ratio when cultured under 50% nature light intensity, they reached the peak andincreased by 56.6% and 29% when NO₃^-:NH₄⁺ ratio was 85:15 under low light comparedwith pure nitrate nutrition; 2) content of nitrate significantly decreasecd with the decreasingof NO₃^-:NH₄⁺ ratio, but content of soluble sugar and Vc decreased without significance.3, Proper NO₃^-:NH₄⁺ ratio improved physiological index of pakchoi grown under lowlight intensity. 1) when NO₃^-:NH₄⁺ ratio was 85:15, photosynthetic rate and leaf area ofpakchoi were increased by 12% and 19%, respectively in the treatment of 50% nature lightintensity; 2) contents of chla, chlb and total chlorophyll were also increased with NH₄⁺ ratioincreasing in weak light.4, Proper NO₃^-:NH₄⁺ ratio increased accumulation and assimilation of carbon andnitrogen. 1) Under 50% nature light intensity, total carbon and nitrogen accumulation inblade, petiole and root of pakchoi reached a maximum when NO₃^-:NH₄⁺ ratio was 85:15,and increased by 47.1%, 69.7%, 26.2% and 40.5%, 44.8%, 34.3%, respectively; 2) rootactivity of pakchoi was also highest when NO₃^-:NH₄⁺ ratio was 85:15, but the content ofnitrate uptake decreased in accordance to increasing of ammonium rate.So, in protected cultivation, the loss of yield caused by low light could remedy partlyby the means of adjusting different NO₃^-:NH₄⁺ ratios in solution, that has a significant guideto practice product.