Response Of Soilless Tomato To Different Nitrogen Forms And Concent Rations

Tomato is one of the major economic crops in the northwestern China. To pursue the maximum tomato yield, farmers completely make nitrogen management according to their experience which is far exceed the vegetable requirement. This not only decreased the tomato yield and fruit quality, but also prevented the utilization of nitrogen largely. The aims of this study were to explore the optimal nitrogen application strategy with high yiled,quality and efficiency synchronously. Soilless tomato experiment was consist of three different nitrate/ammonium ratios: 100:0, 75:25 and 50:50(named N100, N75+A25 and N50+A50, respectively), and three different nitrogen concentrations: 1/4, 1/2 and 3/4 times of standard Hoagland formula(named N1, N2 and N3, respectively). The influencing mechanism and coupling effects of different nitrogen forms and concentrations on tomato growth index, root character, dry mater accumulation, yield, quality and nutrition upake were explored. Based on that, the principal component analysis, grey correlation analysis and TOPSIS model based on AHP and entropy method were used to comprehensively evaluate the indexes of high-yiled, high-quality and high-efficiency, and to explore the optimal nitrogen form and nitrogen concentration application. The main results were as follows:(1) Under the same nitrogen concentration, plant height was decreased with increasing of ammonium proportion and obtained the maximum under N100 treatment. Stem diameter and leaf area both showed an increasing trend with increasing the proportion of ammonium in the nutrient solution, and reached the maximum value when the proportion of ammonium was 25 percent; above that level, stem diameter and leaf area were decreased. Under the same nitrogen forms, plant height and stem diameter increased with the nitrogen rates application and reached the maximum at N2 rate; they were then decreased as nitrogen rates application increased. Leaf area was increased with increasing nitrogen rates. In general,stem diameter was thin under N1 treatment which was not benefit for the development of vascular bundle and the nutrients transport to the aboveground, leaf area was larger which might prolong the plant growth period. Thus the combination of N75+A25 and N2 treatment was the most suitable nitrogen strategy for tomato growth. Furtheremore, thechange of plant height, stem diameter and leaf area showed a Logistic trend over the growth period.(2) The chlorophyll a, carotenoid and chlorophyll a+b showed a first increase and then decrease trend over the growth period. They reached the maximum value at 42 days after transplanting under N100 and N75+A25 treatment, while obtained the maximum value at25 days after transplanting under N50+A50 treatment. The chlorophyll b obtained the maximum value at 42 days after transplanting under N100 treatment, and got the highest value under N75+A25 and N50+A50 treatment at 25 days after transplanting. Therefore, the tomato plants should be promptly fertilized form 25 days to 42 days after transplanting to guarantee the plant growth and yield increase.(3) Root activity showed an increasing trend over the growth period and reached the maximum at first fruit enlargement, and then decreased. Under the same nitrogen forms,root activity showed an increasing trend with increase of proportion of ammonium in the nutrient solution, and reached a maximum when the proportion of ammonium was 25 percent. For a given nitrogen forms, the root activity showed an increasing trend with increases of nitrogen rates, and reached the maximum at N2 rate. Above that level, root activity showed a decrasing trend.(4) The accumulation of plant dry biomass were higher at second fruit enlargement stage and harvesting stage, and the accmulaiton of this two stage under N100, N75+A25and N50+A50 were 80.33 percent, 77.13 percent and 72.14 percnet of total plant dry biomass. The proportion of plant leaf and stem dry biaomass at seedling stage uner N75+A25 N2 treatment were high, and showed an decreasing trend over the growth period.The proportion of plant fruit dry biomass showed an increasing trend over the growth period.N75+A25 treatment promted the plant dry biomass transcolation to the fruit.(5) Increasing the proportion of ammonium in the nutrient solution, total tomato yield showed an first increasing trend and then decreased, and the minimum yield obtained at the N50+A50 treatment which mainly due to the incidence of blossom end rot(BER). The incidence of BER in N50+A50 treatment were about 193% and 110% higher than those under the N100 and N75+A25 treatments. Under the same nitrogen forms, tomato yield increased with increases of nitrogen rates, and reached a maximum at N2 rate, then decreased. Partial factor productivity of nitrogen(PNP) showed a decreasing trend with increases of nitrogen rates. PNP under N3 was about 163%, 152% and 191% lower than those under N1 treatment in N100, N75+A25 and N50+A50 treatment, respectively.(6) Under the same nitrogen forms, organic acid, lycopene and total soluble solid increased with increasing nitrogen rates and reached the maximum at N3 rate, vitamin C,soluble sugars and sugar-acid ratio obtained the maximum value at N2 rate. Under the same nitrogen concentrations, organic acid and total soluble solids increased with the increasing proportion of ammonium in the nutrient solution, while the lycopene, vitamin C, soluble sugars and sugar-acid ratio follow the same order: N75+A25 > N100>N50+A50. By using entropy weighting method, the objective weights of six single quality attributes were calculated based on measurements of these attributes. The subjective weights of these six attributes were calculated based on the analytic hierarchy process(AHP) from survey data from both consumers and horticulture experts. Based on these, the comprehensive weighting method was used to determine the balanced weight of single tomato quality attributes. Results indicated that the attributes were ranked based on their importance by soluble sugar > lycopene > Vitamin C > sugar-acid ratio > organic acid > soluble solid.(7) The highest total root length, root surface area, root volume and root dry weight were all obtained when the proportion of the ammonium was 25% in the nutrient solution,and the minimum values was obtained when the ammonium was 50% in the nutrient solution. The highest root diameter and the minimum root length were both obtained under N50+A50 treatment which indicated that ammonium nutrition promote the short and thick root, but the nitrate nutrition was the opposite. By doing Pearson correlation analysis between root length of different diameter and comprehensive principle component, found the root of diameter less than 1mm got highest correlation, so treat the root of diameter less than 1mm as main absorption root; A significant liner relationship between the main absorption root length, root surface area and root volume and yield, indicated that the main absorption root can reflect tomato production.(8) Plant nutrient uptake showed an increasing trend over the growth period. Second fruit enlargement had the highest nutrient accumulation amount which corresponding to the rapid accumulation of dry biomass in this stage. The total plant nutrient uptake followed the order: potassium > nitrogen > calcium > phosphorus > magnesium, which indicated that tomato preferred potassium nutrition. The nitrogen and phosphorus accumulation in different organs were as follows: fruit > leaf > stem > root. Potassium accumulation in different organs was as follows: fruit > stem > leaf > root. Calcium and magnesium accumulation in different organs were as follows: leaf > stem > fruit > root. Nitrate nutrition promoted the plant uptake for potassium, calcium and magnesium. The co-presence of ammonium and nitrate in the nutrient solution promote the plant uptke for nitrogen and phosphorus. Almost 50% of nitrogen, phosphorus and potassium absorbed accumulated in the tomato fruit. Calcium and magnesium mainly accumulated in the tomato leaf. The BER incidence had good relationship with fruit Ca and K/Ca ratio.(9) Three models of critical nitrogen concentration dilution curve were constructed for the aboveground dry matter in tomato with different nitrate / ammonium rate. A negative power function correlation was found between shoot maximum dry matter and critical nitrogen concentration in different nitrate/ammonium rate treatments and there existed some differences between models of different nitrate/ammonium rates. The difference of the coefficient a between three models showed that the capacity of nitrogen uptake in N75+A25was higher than that in N100 and N50+A50 for the same aboveground biomass. The parameter b showed N75+A25could slow plant senescence, and the leaf nitrogen concentration of which decreased slower than N100 and N50+A50, so the slope of N75+A25 was low. According to the N nutrition index and N deficit model under critical N concentration, N75+A25 N2 could be used as the optimum N application combination. The calculated NNI based on the critical N dilution curve model had a significant correlation with relative aboveground biomass, relative N accumulative uptake amount and relative yield. The critical nitrogen concentration dilution curve model had specific biological meaning. The results calculated based on the model were suitable and reliable, which provided a theoretical basis for dynamic precision fertilization.(10) The principal component analysis, grey correlation analysis and TOPSIS model based on AHP and entropy method showed the consistent results in terms of comprehensively evaluating tomato yield, fruit quality and fertilizer use efficiency. The N75+A25 N2 treatment with nitrate / ammonium ratio of 75:25 and nitrogen concentration N2 rate was the best combination for soilless tomato.