A Comparison of Three Different Hydroponic Sub-systems (gravel bed, floating and nutrient film technique) in an Aquaponic Test System

Murray Cod, Maccullochella peelii peelii (Mitchell), and Green Oak lettuce, Lactuca sativa, were used to test for differences between three hydroponic subsystems, Gravel Bed, Floating Raft and Nutrient Film Technique (NFT), in a freshwater Aquaponic test system, where plant nutrients were supplied from fish wastes while plants stripped nutrients from the waste water before it was returned to the fish. The Murray Cod had FCR's and biomass gains that were statistically identical in all systems. Lettuce yields were good, and in terms of biomass gain and yield, followed the relationship Gravel bed > Floating > NFT, with significant differences seen between all treatments. The NFT treatment was significantly less efficient than the other two treatments in terms of nitrate removal (20% less efficient), whilst no significant difference was seen between any test treatments in terms of phosphate removal. In terms of dissolved oxygen, water replacement and conductivity, no significant differences were observed between any test treatments. Overall, results suggest that NFT hydroponic sub-systems are less efficient at both removing nutrients from fish culture water and producing plant biomass or yield than Gravel bed or Floating hydroponic sub-systems in an Aquaponic context. Aquaponic system designers need to take these differences into account when designing hydroponic components within aquaponic systems.     

十年来中国无土栽培的进展

我国的无土栽培起步较晚,1975年只在温室内开始小面积生产,1989年全国已发展到8公顷。目前生产上采用的主要方式有袋培、槽培和少数营养液膜系统栽培。无土栽培所需要的设备和化肥已经全部国产化。现正在研究降低生产成本,有机肥和化肥混合使用,改进灌溉系统并提高生产效益。     

Performance of wick irrigation system using self-compensating troughs with substrates for lettuce production

Subirrigation systems in which water and nutrients are supplied to the substrate through wick strips for upward nutrient solution (NS) movement can be a feasible alternative to improve lettuce quality with low environmental pollution, enabling production with reduced labor and electricity or in regions with high air temperature. The objective of this study was to compare the performance of two wick irrigation systems using self-compensating troughs filled with either pine bark (WPB) or coconut coir (WCC) with nutrient film technique (NFT) hydroponic system for greenhouse lettuce production. The daily monitoring of electrical conductivity (EC) and pH allowed the experiment management according to the recommended values for optimal lettuce growth. The EC showed variation among troughs and salt accumulation in substrates, with WPB exhibiting two times greater EC than WCC (ranging from 0.95 to 7.57 and from 0.68 to 3.67 dS·m^?1, respectively), while the pH values were stable over time. The WCC promoted greater root length and shoot diameter, while WPB produced shorter plants compared to the other two treatments. NFT resulted in an 83% lower leaf area and 44% lower root volume than WPB and WCC. The fresh and dry shoot masses with NFT were 58% and 24% lower than with WPB and WCC, respectively. The fresh root mass was also reduced in NFT plants, which was 67% smaller than WCC and 59% smaller than WPB. Root dry mass of NFT was 35% lower than the average of WPB and WCC. Nitrate (NO₃)-nitrogen (N), ammonium (NH₄)-N, phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), boron (B), copper (Cu), iron (Fe), manganese (Mn), and zinc (Zn) concentrations in plant shoot and root at the end of the experiment as well as the same nutrients, chloride, sodium, and bicarbonate concentrations in substrate and NS determined weekly differed among the treatments (P < 0.01). The EC and nutrient concentration in the substrates increased over time. The wick irrigation system with both substrates resulted in higher productivity than NFT, with higher yield and plant quality in WCC, indicating its feasibility as an alternative system for lettuce production in greenhouses. However, due to the salinity buildup, water and nutrition management needs to be optimized for self-compensating troughs to avoid an increase in substrate EC over time.     

Nitrogen fixation by annual forage legumes and its contribution to succeeding wheat in the Ethiopian highlands

Soil fertility is declining in most agro‐ecosystems in sub‐Saharan Africa, and incorporation of forage legumes into production systems to utilize the nitrogen fixed by the legumes could alleviate the problem, if efficient nitrogen‐fixing legumes are used. The amounts of nitrogen fixed by Lablab, Medicago, Trifolium, and Vicia species and their contribution to the following wheat crop were estimated in field experiments on an Alfisol at Debre Zeit in the Ethiopian highlands. The amounts of nitrogen (N) fixed ranged from 40 kg N ha^‐1 for T. steudneri to 215 kg N ha^‐1 for L. purpureus. The increase in grain yields of wheat following the legumes ranged from 16% for T. steudneri to 71% for M. tranculata where no N fertilizer was applied to the wheat. Additional N fertilizer applied to wheat at 60 kg N ha^‐1 had no significant effects on wheat grain or straw DM andN yields. In another experiment, eight lablab treatments consisting of factorial combinations of two cultivars (Rongai and Highworth), two Rhizobium inoculation treatments (inoculated and uninoculated) and two times of harvest (for hay at 50% flowering and for seed at seed maturity), were compared on lablab forage production and N yield, and residual effects on two succeeding wheat crops. Inoculation had no significant effects on nodulation, shoot DM or N yields. Rongai had significantly higher shoot DM and N yields than Highworth. Lablab harvested at flowering had significantly higher shoot DM and N yields than lablab harvested at seed maturity. Grain yields of the first wheat crop following the various lablab crops were 93–125% higher than grain yields of the wheat following wheat (continuous wheat) where no N fertilizer was applied. Therefore, lablab is a potential forage crop for incorporation into cereal production systems to improve feed quality and to reduce dependence on N fertilizers for cereal production.     

QUARTZ PORPHYRY TREATMENT ALTERS IRRIGATION WATER CHEMISTRY,AFFECTING HYDROPONIC VEGETABLE PRODUCTION

This study focused on using quartz porphyry (QP) as a water treatment to improve hydroponic production of komatsuna (Brassica rapa L. nothovar; Japanese mustard spinach). We compared the chemistries of the control and QP-treated nutrient solutions and found that magnesium (Mg²⁺) and calcium (Ca²⁺) concentrations increased linearly up to day 21 following sowing in both conditions, then declined slightly. The QP treatment reduced sodium (Na⁺) and chloride (Cl^?) concentrations for the whole cultivation period. In both the control and QP-treated solutions, nitrate (NO^? ₃) and sulfate (SO^2? ₄) showed the same trend to a daily increase. In spite of these similarities, however, komatsuna production was better with the QP-treated nutrient solution compared to control. Treatment with QP during cultivation in August–September reduced the harmful effects of Na⁺, chloride (Cl^?), nitrite (NO^? ₂), and SO^2? ₄ by reducing concentrations of these ions, possibly leading to decreased salinity and toxicity effects in the plants. Mineral concentrations during October–November differed from those of August/September, resulting in variation among the different growth parameters for komatsuna.     

不同营养液浓度对莴苣生长特性的影响

 以长叶莴苣( Lactuca sativa var．1ongifolia Lam．)为试材，研究了NFT栽培条件下莴苣水分与养分吸收特性，以及NFT对其生长发育的影响。试验结果表明，莴苣蒸腾效率前期>中期>后期；整个生育过程中，P、K、Mg的吸收成分组成浓度(养分与水分吸收比，n/w)均低于原始营养液浓度，而Ca则相反；NO3^--N因处理浓度不同而异。叶片中各无机成分含量随生育过程而提高，同一生育期随营养液浓度提高而增加；综合莴苣产量因子与商品性状，以3/4倍园试均衡液最佳。     

Deployment of Sawdust as Substrate Medium in Hydroponically Grown Lettuce

In this study, lettuce plants were grown in sawdust (Saw) and/or perlite (Per) mixtures (sawdust; Saw:Per 75:25%; Saw:Per 50:50%; Saw:Per 25:75%; Perlite) and in Nutrient Film Technique (NFT), in an unheated greenhouse. Plants grown in NFT were taller with greater leaf area resulting in greater fresh weight. Sawdust addition reduced leaf length, leaf area and as a consequence the fresh weight but not the leaf number. However, leaf dry weight increased as sawdust content increased into the substrate. Leaf chlorophyll reduced but leaf fluoresces increased in perlite and NFT. High sawdust content (75% or 100%) reduced photosynthetic rates and stomatal conductance. Nutrient uptake [potassium (K), sodium (Na), phosphorus (P)] was the greatest in NFT treatment, while perlite and Saw:Per 25:75% increased elemental uptake (up to 74%) comparing with the remaining treatments. Leaf elemental analysis fluctuated among treatments. Thus, low content (i.e. 25%) of sawdust in perlite could improve inorganic substrate media properties.     

高温胁迫条件下营养液膜水培樱桃番茄的逆境适应性

通过测定高温处理后水培和土培樱桃番茄的几项生理指标,研究了樱桃番茄在高温胁迫条件下的叶水势、光合速率、SOD酶活性等生理指标的变化特征,结果表明,高温胁迫条件下土培番茄叶水势、光合速率和SOD活性大幅度下降,而水培番茄上述生理指标虽有下降,但幅度远较土培番茄为少,因此,水培樱桃番茄对高温的抵抗能力要强于土培。     

Effect of NO3 and NH4 concentrations in nutrient solution on yield and nitrate concentration in seasonally grown leaf lettuce

The effect of suboptimal supply of nitrogen (N) and of replacing nitrate in the nutrient solution with ammonia on growth, yield, and nitrate concentration in green and red leaf lettuce was evaluated over two seasons (autumn and spring) using multiple regression analysis. The plants were grown in a greenhouse on a Nutrient Film Technique (NFT) system. Nitrogen concentrations in the nutrient solution were either 3?mM or 12?mM, and the form of N was varied as follows: 100% NO₃, 50% NO₃?+?50% NH₄, and 100% NH₄. In both seasons, the biomass (fresh weight) of lettuce heads increased with increasing NO₃ concentrations and in autumn, NO₃ even at 1.5?mM was sufficient for high yield. However, head dry weight was affected neither by the season nor by changes in the composition of the nutrient solution. The concentration of NO₃ had no effect on root dry weight, but it decreased at higher concentrations of NH₄. The number of leaves increased as the ratio of NO₃ to NH₄ in the nutrient solution increased and was higher in autumn because of the longer growth period. Increasing the concentration of NO₃ in nutrient solution increased both total N and nitrate concentration in lettuce heads (dry weight) but decreased the concentration of total C. Also, leaf nitrate concentration was lower in spring than in autumn and decreased with increasing NH₄ concentration. Nitrogen utilization efficiency was maximum when NH₄ levels in the nutrient solution were either 0% or 50% irrespective of the season. Our results thus show that suboptimal N supply in autumn will not affect lettuce yield, and that nitrate concentration in leaves is lower when NH₄ concentrations in nutrient solution are higher and also much lower in red lettuce than in green lettuce.     

NFT无土栽培营养液溶氧量的研究

本文阐述了在NFT系统上试验探讨营养液溶氧量与环境因子的相关关系,就如何改善溶氧供给,提出若干改进NFT设施设计的建议,如:适当加大贮液池;在贮液池上附设循环液的喷洒装置;适当扩大栽培床的槽腔;夏天采用低温的地下水配制贮液池中营养液,或降低温室(大棚)的气温。