Tomatoes (Lycopersicon esculentum Mill. cultivar Beefsteak) were grown satisfactorily in secondary effluent sewage water from a residential area in Southern California as the nutrient solution but with Fe supplied additionally. Foliar Fe spray was partially satisfactory while soluable Fe chelate and insoluble Fe‐Fe oxide applied to roots were completely satisfactory. Key words: Glasshouse tomatoeshydroponicsagricultural use of sewage waterenergy for fertilizerswater quality

The Fe‐inefficient corn (Zea mays L.) inbred Ys1/YS1 was compared with the Fe‐efflcient WF9 inbred for ability to take up Fe from solution culture at different P levels. A high level of P depressed Fe uptake more in the Ys1/Ys1 than in the WF9 inbred. The Ys1/Ys1 roots were high in P.

Whenever land becomes contaminated with trace metals, most always two or more of the trace metals are in excess simultaneously. Nearly all of the baseline studies of metal excesses, however, have been made with single metals, and such studies do not accurately reflect the critical response levels. Various critical points can shift due to interactions. Analytical data must be obtalned for as many as 20 different elements and their differential distribution among various plant parts, including roots, must be known to galn even a partial understanding of the interactions. Positive and negative synergisms, competition, protection, and sequential additivity are observed among the interactions. The nature of interactions varies considerably with concentration levels, soil pH, soil texture, level of soluble Ca in soil, presence of salinity, differential distribution in soil of the metals present in toxic quantities, presence or absence of chelating agents, soil organic matter levels, and other factors. Interactions are difficult to model. All of these relate to the behavior of Fe in plants and in soil. Iron deficiency is commonly induced by excess levels of other trace metals, both singly and more commonly in various combinations. Such Fe deficiency is complex. Other essential nutrients are involved in somewhat similar interactions. When testing soil for possible problems with Fe deficiency, it is important that concentrations of available trace elements other than Fe in addition to other soil parameters be considered in the equation for prediction.

Satisfactory progress has been made in recent years in preventing and correcting Fe deficiency in plants, and more can be expected in the future. Important advances include uses of acid- and Fe-fortified organic wastes and use of amended sulfur-pyrite mixes in soil. Three different approaches with organics are as an acidified matrix with Fe, as a means of chelating Fe, and as a carrier of acidifiers. Several procedures can help minimize Fe deficiency. (1) Avoid mis-management of soil physical properties and overirrigation. (2) Avoid nutrient imbalance, such as excess P or excess micronutrients. (3) Use preplant application of mildly acid-organic matter-Fe-sulfur or pyrite mixes worked into zones of soil or banded into seed rows. It is important that small bands or spots in soil be completely neutralized of CaCO3. (4) Where foliar sprays can or need be used, especially to correct mild chlorosis, use ferrous compounds prepared to be delivered at pH 3± so that the Fe does not easily oxidize or precipitate in the solution. (5) For established trees that have become Fe deficient, inject, via slant drilling of small holes in tree trunks, dilute ferric ammonium citrate sufficient to supply not more than 100 mg kg-1 Fe to leaves (dry weight basis). Most but not all species will respond. Procedure may be repeated in two or three weeks if necessary. (6) Iron chelates may be used in drip irrigation. If soil is sandy, soil pH not over 7.2, FeDTPA may be used; otherwise, FeEDDHA should be used. If the Fe is supplied with no other nutrients, pH may be at 4 and some FeSO4 included to recycle the chelating agents. If Fe is used without chelating agents, the pH may be 1.0 or less and other nutrients included. (7) Urea-acid sulfate-Fe sulfate may be irrigated into soil around plants, especially if soil was polymer treated. (8) Efficiency of use of Fe chelates may be increased by making them slow release or by applying with seeds.

Data from a published paper [Rehm (1984)] were used to illustrate different interactions encountered between N and P fertilizers in a five‐year field test of a mixture of grasses. In a 5 × 5 factorial experiment, sequentially additive, synergistic, slightly synergistic, and Liebig‐synergistic responses were all observed. Therefore, there were instances of Liebig‐type limiting factors, Mitscherlich‐type limiting factors, and in‐between gradations. There was little indication of antagonism between N and P. The relationships observed between yields and N doses indicate an increasing critical dosage for P with increasing N.

Because vegetative parts of grass species are generally high in Si, monocot and dicot plants were grown in steam-sterilized soil to further test the hypothesis that there is competition between N and Si for plant uptake. Silicon uptake by dicots is low, so the species tested in this study was not sensitive to changes in Si with N differences. With monocots, N decreased Si uptake, but NH4+-N decreased it more than did NO3−-N in wheat. In contrast, the NH4+ increased uptake of Fe, Al, Cu, and Zn, but not Mn. The results were explainable, at least in part, on the effects of exchange of NO3− for OH−, and NH4+ for H+ in the uptake process. With corn and barley, a high P application resulted in increased Si in shoots of plants only at low N levels. Leaf concentrations of Si, Fe, Al, Cu, and Ti were generally higher in barley than in corn.

Bush bean plants were grown in nutrient solution with treatments to result in stresses of CaCO3 (Cu deficiency), excess Cu, and P deficiency. When moderate P deficiency and high Cu toxicity were both simultaneously imposed, the interaction resulting in poor growth was synergistic when the solution pH was about 4. When the solution pH was about 8, the interaction was less synergistic. The high pH considerably suppressed the uptake of the Cu. The results are further evidence that liming can decrease much of the interactive synergistic effects of toxic concentrations of multiple trace metals. Low P resulted in increased Cu in roots at the low pH. The P deficiency was more conductive to Fe deficiency induced by high Cu than was adequate P.

We grew bush beans (Phaseolus vulgaris L. cv. Improved Tendergreen) in nutrient solutions with two elevated levels of Zn and two of Co singly and in factorial combination. Levels were high enough to result in some toxicity in comparison with a control in which no Co and an adequate amount of Zn were added. In relationship with the control treatment, the low Co treatment increased vegetative yield, while the high Co decreased yield. The ability of the low Co level to increase yield was a function of the applied Zn level. Yield increases for low Co were 31, 11, and 0%, for increasing levels of Zn. Both elevated Zn levels were toxic. When the elevated levels of Co and Zn were interacted, synergistic, additive, and protective effects were all observed. Phosphorus, Fe, Co, and Zn concentrations in plant parts were involved in the interactions. The combination of highest Zn and Co resulted in most depression of Fe in leaves. Cobalt somewhat suppressed the ability of high Zn to depress uptake of K + Ca + Mg, which effect decreased synergism. The protective effect was the result of Zn depressing leaf concentration of Co.

Bush beans (Phaseolus vulgaris L. cv. Improved Tendergreen) were grown 14 d in nutrient solution culture in a factorial experiment in which three Ca levels (10−1, 10−3, and 5 x 10−3 N) were interacted with four of Zn (none added, 10−5 2 x 10−5 and 10−4 M). The major objective was to determine if increasing Ca overcomes Zn toxicity either by decreasing Zn uptake by plants or by increasing plant tolerance to Zn. At low Zn levels, increasing Ca had no effect on Zn concentrations in either leaves or roots. At high Zn levels, increasing Ca resulted in more Zn in both leaves and roots, although the effect was most pronounced in roots. Zinc treatments resulted in much greater differences in Zn concentrations in roots than in leaves. When Ca ameliorated the effects of excess Zn, the mechanism seemed to involve increased tolerance to excess Zn.

Bush bean plants (Phaseolus vulgaris L. cv. Improved Tendergreen) were grown in nutrient solutions at pH maintained near 5 for 21 d following transplanting. In addition to a control treatment, five different trace elements were applied in modest excess at levels predetermined to give around 10% yield reduction each, i.e., M, 6 x 10−6 Cu, 5 x 10−7 Ni, 10−6 Co, 10−5 Zn, 4 x 10−7 Cd, all as sulfates. Some multiple combinations were used in addition to the single element treatments, i.e., Cu-Ni-Co-Zn, Ni-Co-Zn-Cd, Cu-Ni-Co-Cd, Cu-Co-Zn-Cd, Cu-Ni-Zn-Cd, and Cu-Ni-Co-Zn-Cd. Growth effects of the trace element combinations were protective; there was more growth than was additively predicted. Part of the protection was due to Co suppressing uptake of Cd by roots. Other trace elements in turn suppressed uptake of Co by roots. The concentration of Na in leaves appeared to be a sensitive indication that stress really was greater with the combination of four trace elements in modest excess than with just one. Relative to the control of 1.00, the average yield of the single element treatments in slight excess was 0.91. In various combinations of four trace elements, the average relative yield was 0.73.

The effect on growth of the interaction between the osmotic effect of NaCl and the specific ion toxicity of Ni was studied using lettuce in completely defined nutrient solution. In seedling lettuce, NaCl exerted both a specific ion effect and a salinity or osmotic effect. The specific ion effect was exhibited at relative low concentrations of NaCl and resulted in minimal yield depression. The salinity or osmotic effect was exhibited at higher concentrations of NaCl and was associated with a reduction in water potential. The controlling influence of water potential was verified by a similar dose-response curve developed under PEG (polyethylene glycol) 6000 and high-strength nutrient solution. The Ni was toxic at a relatively low concentration of 10 μM L−1 and thus by itself contributed only specific ion toxicity. The Ni dose-response curve was biphasic with a toxicity threshold at 10 μM L−1 and a phase change at 30 μM L−1, which was associated with an 87% yield reduction. The interaction between Ni and NaCl must be described in terms of both Ni effect on NaCl and NaCl effect on Ni. The interaction of NaCl on the Ni dose-response curve was additive in the first phase. The type of interaction, although also occurring in the second phase of the Ni dose-response curve, was not clear in these studies. The interaction of Ni on the NaCl dose-response curve was primarily on the specific ion toxicity portion of the curve with little effect in the osmotic part of the curve. At low levels of Ni, such as 10 μM L−1, Ni protected against toxicity from NaCl. The toxicity threshold of the first phase of the NaCl curve was shifted toward being less sensitive in the presence of high concentrations of Ni. Thus high concentrations of Ni (toxic levels) decreased to some degree the specific ion effect of Na. Analysis of plant tissue indicated that absorption of Na was reduced by Ni.

Excess Cu and NaCl in nutrient solution gave additive interactions and positive and negative synergisms on vegetative growth of bush beans; these were independent of wilting of plants. Salinity had relatively little effect on Cu concentration of leaves and stems. Copper increased the concentration of Na in leaves and stems at the high-salinity level. The intermediate concentration of Cu generally increased concentrations of Fe and Mn in shoots, but the high Cu level decreased them. There were some instances of impaired Ca transport at high Cu levels. The CaCO3 used to increase solution pH was also inhibitory of growth and in an additive manner with NaCl. The CaCO3 induced a mild Cu deficiency at a low Cu level and decreased Cu toxicity at high Cu levels. The high pH (with CaCO3) decreased Cu toxicity by decreasing its uptake. The highest yield of shoots in the experiment was with the highest Cu level at the 0.01 M NaCl and at the high pH. There was a 33% yield response to the NaCl. The same levels of Cu and NaCl at low pH were very toxic; differences were in Cu and Na concentrations in plants.

Dose-response curves were obtained in a background of 1/10 strength Hoagland nutrient solution for lettuce seedlings with Ni at different background levels of CaCl2 and for CaCl2 at different background levels of Ni. Nickel showed a toxicity threshold at 20 μeq L−1 of Ni and a 50% reduction in yield at Ni concentrations of about 30 μeq L−1. However, if the available Ca was increased from that in the control 1/10 strength Hoagland solution of 1.0 to 257 meq L−1, most of the reduction in growth due to Ni toxicity at 30 μeq L−1 was reversed, giving a yield of better than 90% of control. This concentration of Ca (CaCl2) was where Ca started to have a salinity effect and further increases of Ca resulted in yield decrease due to salinity, so that any further alleviation of the Ni toxicity was not discernible. When an Ni dose-response curve was run in the presence of high background concentrations of Ca, Ni concentrations close to its toxic threshold level provided some alleviation of the salinity stress. These curves also showed a strong alleviation of Ni toxicity at high Ni concentrations in the presence of high background concentrations of Ca.

If crop yield is not maximum, it is due to the additive or synergistic accumulation of all stresses to which the crop is exposed. The stresses do not act independently. If yields are increased, it is because of removal or overcoming of stresses to approach the potential of yield maximum. If four different plant nutrients are present in supply and ratio each at 90% of optimum and if all other nutrients are optimum, the additive summation of the nutrient stress is 0.90 x 0.90 x 0.90 x 0.90 = 66%. Then 66% of yield maximum is possible if the interactions are sequentially additive. This assumes Mitscherlich-type limiting factors. Small departures of several nutrients simultaneously from optimum are thus a serious barrier to obtaining yield maximum. When Liebig-type limiting factors remain, little or no response to inputs to correct Mitscherlich-type limiting factors can be expected until those of the Liebig type are removed and in order of which is in greatest limitation. Once this type of limiting factor is removed, responses to additional inputs can be obtained. In contrast, it does not matter in which order Mitscherlich-type limiting factors are corrected. Severe deficiencies generally are of the Liebig-type, and slight deficiencies are of the Mitscherlich type.

We applied new-generation soil conditioners to sodic soils in various procedures. In flocculation tests, followed by wet-sieving, particle sizes were approximately four to five times larger with new soil conditioners than with an older soils Conditioner (Krilium) or with controls. Water penetration was greatly improved on a sodic soil when conditioned with the new soil conditioner. A Natrargid soil was amended with NaCl, NaHCO3, and NaOH to give different degrees of sodicity. Application of polyacrylamide in solution to all the soils increased seem emergence and dry weights of tomato seedlings.

An iron-inefficient cultivar of soybean (Glycine max L. Merr. Bragg cv. PI-54619-5-1 was grown in two different calcareous soils, a Natrargid and a Torrifluvents, to determine if improvement of soil aeration with a synthetic polyacrylamide as a soil conditioner would decrease the tendency of the cultivar to lime-induced chlorosis. The results suggest that when soil is well aerated with good drainage from use of the soil conditioner, the iron status of plants is improved.

Synthetic soil conditioners that were available more than 30 years ago were shown to improve properties of soil related to water usage. Those results obtained 30 years ago are still valid. The major difference with present results is that they can now be obtained with much lower concentrations of new polymers. One reason for low rates is application of polymers in the irrigation water, in contrast to the procedure of applications of dry powder to soil 30 years ago. Low concentrations of polymers in the irrigation water increase water penetration into soils; different soils need different concentrations.