NITROGEN EFFECTS ON CHLOROSIS IN MACADAMIA

C. P. North and A. Wallace’

Reprint from CMS 1959

Macadamia trees often become chlorotic in both lime and non-lime soils. Lime-induced chlorosis, which usually is a form of iron deficiency, is induced in many plant species by excess lime (calcium carbonate) in the soil and complicated by cold temperatures and high soil moisture. Many things, such as nutrient unbalance or poor aeration may induce chlorosis in non-lime soil, on susceptible varieties or individuals.

Some field-grown macadamias at the University of California at Los Angeles became chlorotic after nitrogenous fertilizer was applied. Since nitrogen affects the absorption and utilization of other nutrients, an investigation of the affect of nitrogen level in relation to the iron status of Macadamia was initiated.

Since the deficiency symptoms of leaves of Macadamia were not available, plants were set up in sand culture to determine the chlorosis patterns for iron, manganese, and zinc deficiencies.

All plants used in these investigations were rooted cuttings of varieties that have developed chlorosis in non-lime soil. Hawaiian 491 and Australian F varieties were used for the nitrogen level experiments in soil. They were planted in one-gallon cans of virgin clay loam amended with Krillium to insure good drainage. Faulkner cuttings in one-gallon glazed crocks of No. 16 silica sand were used for nitrogen level trials and for the effect of nitrate nitrogen on Macadamia. Hawaiian 246 and Australian J-3 in 6-inch plastic pots of No. 16 silica sand were used in the deficiency-leaf-pattern experiments. There were four or more plants in each treatment except for the Hawaiian 246 plus manganese that had three replications and Hawaiian 491 IX nitrogen level where two of the four replicates died.

The deficiency-leaf-patterns were produced by omitting a micronutrient from an otherwise complete nutrient solution. Australian J-3 and Hawaiian 246 were used in minus iron, minus manganese and minus zinc treatments. Another series of Hawaiian 246 received only one (1) micronutrient and boron; these were called plus iron, plus manganese, and plus zinc. Complete nutrient controls were used in all experiments.

All plants were grown in a glasshouse, with a minimum temperature of 60 F., from September 1956 to September 1957.

The sand cultures received nutrients daily except on weekend. Soil cultures received nitrogen weekly when the plants were small and monthly as the plants grew larger. Nitrogen levels were multiples of the lowest level. I.e., 1X, 2X, 3X, and 4X. Nitrogen was applied as ammonium nitrate so that only nitrogen ions would be added to the cultures.

The nitrate nitrogen sand cultures received complete nutrient solution with nitrogen as potassium and calcium nitrates to give 210-ppm nitrogen. The control plants, in the nitrate nitrogen trials, received 210-ppm nitrogen with 175 ppm as nitrate and 35 ppm as ammonium.

Initially the deficiency-leaf-pattern plants received only 140-ppm nitrogen, from calcium nitrate, but it soon became apparent that the plants were not developing normally and the nitrogen was increased to 210 ppm with ammonium nitrate.

Experimental Results and Discussion

The sand culture-deficiency and nitrogen level results will be discussed first to give information on nutrient levels in the leaves of healthy anti deficient plants. All sand cultures were grown from September 1956 to January 1957 with the following nutrient solution:

This solution was kept relatively low in nitrogen because some Macadamia plants, in the field, became chlorotic following nitrogen applications.

Faulkner cuttings were placed in sand, at least four replications in each group, with three levels of nitrogen, 140-ppm (calcium nitrate) 196 ppm (calcium nitrate plus ammonium nitrate), and 252 ppm (calcium nitrate plus ammonium nitrate) in the above nutrient solution.

All plants in these two experiments that were receiving 140 ppm nitrogen developed interveinal chlorosis, similar to iron deficiency, by January 10, 1957. The Faulkner cuttings receiving 196 and 252 ppm nitrogen did not develop chlorosis, during this period, or show any other abnormal symptoms. It was thus evident that up to 252-ppm nitrogen would not cause chlorosis. The plants were left at their initial nitrogen levels until February 13, 1957 when the low level was raised to 252-ppm, the medium level to 303-ppm and the high level to 364-ppm. The nitrogen level of the deficiency plants was also raised to 252-ppm.

Following the change in nitrogen level from 140-ppm as nitrate only to 252-ppm with ammonium nitrate, all plants became greener. This raised the question as to whether the greening was due to increased total nitrogen or to the ammonium fraction of the total nitrogen. The investigations of Cain (3) with blueberries, Willis and Carrero (10) with rice, and Colgrove and Roberts (4) with azaleas showed that those plants developed chlorosis when receiving nitrogen only in the form of nitrate. Accordingly, on March 7, 1957, the nitrogen sources of the Faulkner plants were changed so that the low level plants were receiving 210-ppm nitrogen as nitrate only, the medium level plants received 210-ppm nitrogen including 33-ppm ammonium nitrogen from ammonium nitrate, and the high level plants were left at 364-ppm nitrogen (252-ppm nitrate nitrogen and 112-ppm ammonium nitrogen). The deficiency plants also were changed to 210 ppm nitrogen with 70-ppm. as ammonium nitrate.

By April, chlorotic patterns had disappeared from all the plants that were receiving iron regularly. The minus iron plants became green after they received ten applications of complete nutrients in February but the chlorosis was reappearing by the first of April.

Leaf samples were taken on April 5th from the Hawaiian 246 and Australian J-3 control plants, the Hawaiian 246 minus and plus iron plants, and from the Faulkner nitrogen level plants in sand to obtain information on the current nutrient status of the plants. These samples represent the youngest mature or nearly mature leaves on the plants. Table 1 gives the analyses of these leaves together with the range of nutrients found in green and chlorotic leaves of Bhangoo and Wallace (1) and the tentative adequate and deficient levels given by Cooil (5).

The analyses indicate that all plants were receiving more than adequate nutrition, excepting iron, when judged by the findings of Bhangoo and Wallace (I) and Cooil (5).

In view of the diminishing chlorosis, iron seemed to be at the critical level in the 246 control and (-4-) iron plants, but well below the critical level in the (-) iron plants. The Faulkner plants seemed to have an adequate but not high iron level. The low N plants were never dark green in color, and at the time of sampling was beginning to show a definite interveinal chlorosis.

High phosphorus may have been a contributing cause of the apparently low iron level as shown by the work of Biddulph (2). The data of Guest (6) (7) indicate higher phosphorus content in chlorotic than in normal leaves.

Cuttings of Australian F, with three levels of nitrogen, and Hawaiian 491, with four levels (three replications in each treatment) were placed in soil culture, in one-gallon cans, adjacent to the sand cultures. These plants received nitrogen in multiples of the lowest level (lx, 2X, 3X, 4X). Nitrogen was applied simultaneously to all plants. Applications were spaced weekly at first and monthly as the plants grew larger and more nitrogen could he applied at one time. An effort was made to give the 4X level the greatest amount of nitrogen in each application that would not damage the plant. These plants exhibited interveinal leaf chlorosis with the 2X and 3X level plants worse than the IX and 4X levels. The 4X level showed the least chlorosis and grew the best. Since the soil, virgin clay loam was high in exchangeable manganese it was thought that perhaps manganese was interfering with iron absorption. Leaf samples of the youngest, mature or most nearly mature growth were taken for analysis on April 5th. The results are given in table 2, together with the findings of Bhangoo and Wallace (I) and Cooil (5).

These plants had more than adequate nutrition, with the exception oi iron, when compared to the findings of Bhangoo and Wallace (I) and Cooil (3). The actual and effective iron levels were perhaps lowered by high phosphorus as indicated by the investigations of Biddulph (2) and the data of Guest (6) and (7).

Sideris and Young as reviewed by Robertson (9), found manganese concentrations higher in cultures supplied with nitrates than in the ammonium cultures where iron accumulated; this was thought to be due to antagonism between manganese and ammonium ions. Burstrom, as reviewed by Robertson (9), associated manganese with the uptake of nitrogen and the formation of amino compounds in roots. Since these plants were grow ii in soil and the nitrogen applied as ammonium nitrate, nitrification of the ammonium ions so that mostly nitrate was absorbed by the plant may account for the increasing manganese with the increasing nitrogen levels. There was no correlation between manganese and iron in the plants. ‘The plants with low P/Fe ratios appeared the most normal, with the exception of the 4X nitrogen level. The high nitrogen plants had the greatest manganese and phosphorus levels, but no higher iron level than the other treatments, yet these plants showed the best color and growth. If manganese is necessary for nitrogen metabolism as indicated by Burstrom, reviewed by Wood (11), then the high manganese may have made the nitrogen and phosphorus utilization more rapid, thus preventing inactivation of the iron.

All plants in this investigation were continued to mid-September 1957, when leaf samples of the latest mature foliage were taken and analyzed.

The Faulkner plants in sand culture, from Table 1, were continued with 364-ppm nitrogen including ammonium nitrogen and 210-ppm nitrogen including 35-ppm ammonium nitrogen. The plants receiving some ammonium nitrogen grew well and with good color. The plants receiving the higher nitrogen grew faster and developed larger leaves. In Table 3, the high N plants have more nitrogen than the low N plants, but lower calcium, potassium, magnesium, phosphorus and zinc. Iron is probably the same in both treatments and this is perhaps to be expected since the iron supply was chelated iron. The four replications in each treatment correspond closely in nutrient analysis.

**complete nutrients Feb. 1-10 (to prevent death).

***252364 ppm nitrogen.

****140 ppm N as nitrate Sept. to Feb. 13th; 252 Ppm N to March 7th; 210 ppm N as nitrate only to Sept. 1957 (end of Experiment).

¥ Bhangoo and Wallace (1).

Table 2

Inorganic nutrient content of leaves of Australian F and Hawaiian 491 cuttings in soil culture, three and four levels of nitrogen, after six months of treatment.

Table 3

Inorganic nutrient content of leaves of Faulkner cuttings after 12 months in sand culture with nitrogen as ammonium nitrate as nitrate only.

The plants receiving nitrate nitrogen only grew very well, but the new growth became progressively more chlorotic and developed tip-burn on some of the upper terminal leaves by August four months after the nitrate level was raised from 140 ppm and 210 ppm and approximately ten months after nitrate treatments were started. The leaves on these plants that had developed during the first few months of nitrate treatment and during the three weeks that they received some ammonium nitrogen, remained green. For this reason the leaves of nitrate nitrogen plants were separated, for analysis, into groups as green, pale green, yellow, and yellow with burned tips. Leaf samples of the youngest mature growth were taken from the other two nitrogen treatments. These analyses are given in Table 3 with findirgs of Bhangoo and Wallace (1) and Cooil (5).

Examination of Table 3 reveals much higher phosphorus-to-iron ratio in the yellow leaves than in the green leaves. Even in the pale green leaves the iron seems only marginal when combined with relatively low phosphorus. The yellow leaves were, in general, quite a bit smaller than the green leaves which may account for the apparent accumulation of nitrogen, potassium, magnesium and phosphrus. The size difference would make the iron and manganese levels seem higher also.

The deficiency sand cultures, Table 5, showed an overall drop in leaf-nutrient level. This may have been due to unbalance of root and top areas. The control plants, receiving complete nutrients, were dark green and without chlorotic leaf patterns. Manganese and iron deficiency chlorosis patterns appeared on some of the treatments, but zinc deficiency was not evident as a chlorotic leaf pattern.

Zinc Deficiency. The Hawaiian 245 minus zinc plants were nearly as dark green as the controls, but the upper stems were very slender and developed partial S-curves, apparently from weakness.

The Australian j-3 minus zinc plants did not exhibit interveinal chlorosis hut the leaves were lighter green than the controls. The stems did not show the weakness that was apparent in the Hawaiian 246 group.

Zinc content as low as 11 ppm did not produce noticeable interveinal chlorosis. However, when the leaves contained less than 20-ppm zinc, they were lighter green in color than the control plants. Small leaves and shortened internodes, typical of zinc deficiency in some plants, were not evident on any plant regardless of treatment.

Iron Deficiency. The iron deficiency pattern of chlorosis developed on the leaves of the minus iron and on some of the plus zinc (no iron) plants. This pattern, Fig. I, is a narrow green zone along the veins of thc leaf with the interveinal spaces chlorotic. The green zone is not wedge-shape as it is in manganese deficiency.

Slight interveinal chlorosis seemed to occur when the iron content was below 30 ppm, particularly if the phosphorus content was near 0.20% or higher. However, no chlorosis was present on some plants when the iron content of the leaves was as low as 20-ppm if the phosphorus content was low (approximately 0.10%). Phosphorus levels near 0.20% or greater, of the dry weight, seemed to be correlated with iron deficiency symptoms, particularly if the iron level was below 30-ppm. It will take further investigation to determine the complete correlation of iron and phosphorus in Macadamia.

Table 4

Inorganic nutrient content of leaves of Australian F and Hawaiian 491 cuttings in soil culture, three and four levels of nitrogen, after 12 months of treatment.

Table 5

Inorganic contents of leaves of Hawaiian 246 and Australian J-3 grown in sand culture for 12 months, with nutrient deficiencies as indicated.

Manganese Deficiency. The chlorosis pattern of manganese deficiency, Fig. 1, is a wedge-shaped dark green zone along the midrib and extending along the lateral veins from the midrib. Necrotic spots, typical of manganese deficiency on some plants such as camellia, did not appear on the Macadamia leaves observed; perhaps duration of the deficiency is connected with the necrosis.

Manganese deficiency symptoms did not appear until the manganese content was 10 ppm or less, and then only near the end of the experiment.

Manganese and Zinc Deficiency. These plants received only iron and boron as micronutrients in otherwise complete nutrient solution. There was no chlorotic leaf pattern but the plants were smaller than the controls and the leaves were lighter green in color.

Iron and Zinc Deficiency. These plants received only manganese and boron as micronutrients in otherwise complete nutrient solution. There was slight interveinal chlorosis on the leaves and the color was lighter green than the controls.

Iron and Manganese Deficiency. These plants received only zinc and boron as micronutrients in otherwise complete nutrient solution. Definite manganese and iron deficiency patterns developed on the leaves of these plants that were noticeably brittle The leaves of these plants were the only ones that were brittle.

Some macadamias develop chlorosis in non-lime soils. Sometimes chlorosis has appeared after the addition of nitrogenous fertilizer.

Plants of chlorosis susceptible varieties were grown in soil and in sand culture with varying amounts of nitrogen, as nitrate only, and with ammonium and nitrate nitrogen together. The plants receiving both ammonium and nitrate nitrogen grow well and did not develop chlorosis The plants receiving nitrate nitrogen, only, were always lighter green in color than those receiving some ammonium nitrogen. After about nine months of nitrate nitrogen, the new growth became progressively more chlorotic and finally showed burned leaf tips. All the chlorotic leaves were low in iron and some were very low in manganese. The phosphorus content was relatively high.

Increasing levels of ammonium nitrate, applied to plants in soil, gave increasing levels of manganese in the leaves, but high manganese levels were not correlated with low iron or with chlorosis.

High phosphorus levels, in soil cultures, were closely correlated with chlorosis at iron levels below 40 ppm. It is not known how high the iron content should be (to avoid chlorosis) when the phosphorus level is 0.3 to

0.5%. If this correlation between iron and phosphorus is correct, then it is desirable to know if relatively high iron content, for instance greater than 100 ppm, can be correlated with phosphorus deficiency when phosphorus is less than 0.1%. Further investigation is necessary to study the iron-phosphorus relationship.

This experiment did not show calcium-potassium correlation or the deficient levels of either nutrient.

Iron seems to be the most critical micronutrient and it is thought that the content of the leaves should be 40 ppm or more for normal plants.

Normal plants were grown with a low as 15 ppm but this low level of iron was accompanied by relatively low phosphorus and the plants were grown in a glasshouse. The same plants grown under field conditions might develop chlorosis.

Manganese did appear limiting until the leaf manganese content was less than 10 ppm. No toxicity or chlorosis was observed when the manganese content was 2700-ppm. In the soil cultures manganese was correlated with the nitrogen level applied to the cultures, but was not correlated with iron content or iron activity in the plant. These results are in contradiction to work reviewed by Mueller (8) where, in some legumes, the soluble iron to soluble manganese ratio was very important. Investigations reviewed by Wood (11) show that manganese is important in nitrogen reduction and assimilation. Some Macadamia plants with low iron but high manganese content were more normal in appearance than those with low iron and low manganese.

Low zinc appeared to result in chlorosis hut the deficiency level was not observed.

Magnesium was not observed to be deficient or in excess.

Nitrogen nutrition can result in chlorosis by influencing the absorption and translocation of iron. Nitrate nitrogen is associated with manganese accumulation and rise in pH of the plant sap, while ammonium nitrogen is associated with iron accumulation and lowering of the pH of the plant sap. It is suggested that macadamias be given much of their nitrogenous fertilizer in the form of ammonium salts such as ammonium sulfate, ammonium nitrate and urea.

Applications of chelated iron may he necessary in non-lime soils as well as in soils with excess lime.