I think the basis is rather universal for majority of crops - is determined on the potential yield under particular conditions, especially climatic (above all the water supply). If the particular conditions make possible to obtain 15t/ha of orange, assuming optimal (rather high, because with very low planting density the potential yield would be lower) planting density, we can calculate the export of nutrients with such yield. I think this (crop requirements) should be the base for calculating fertilizer requirements, which should be modified depending on soil fertility - organic matter (determining indigenuous N supply) and other nutrients (P, K, Mg itd). If our soil is high in thesenutrients (or organic matter) we can consider reducing fertilizer requirements comparing with the crop requirements, but if the soil is poor we should increase doses of fertilizers. So I think the spacing between plants is important because it determines maximum potential yields and determines the dose of fertilzer for particular plants. But within certain range of planting densities (close to optimal) enabling the same optimal yield, the fertilizing requirements for unit of area could be the same.

Thanks Michal . Let consider a classical case of citrus. On typical black clay soil of central  India , normal sapcing  is 6m x6m ( Plant-to-plant and row-to-row) using one commercial rootstock and total nitrogen requirement comes out to be 167 kg/ha . But , if same spacing is reduced to 4mx6m ( Plant -to- plant and row-to-row), the fertilizer requirement comes out to be 140 kg/ha on the similar piece of land, simply because  of lower canopy volume . 

Interesting, clearly I did not considered, when the plant are young, they need more nutrients for growth.

But does your result refer to mature plantation, where the trees achieved full dimensions? I remember, that the trees grow all their life, but certainly, when they start to produce they not grow so much. And their "full dimensions" depend on rootstock... Both plantations had the same rootstock?

As you have such results, it would be good to publish them.

Yes , we conducted it using the same same rootstock-scion combination . What I suppose , probably the inherent soil fertility contributes more rigorously under high density planting compared to planting at wider spacing.

So, in this case it would be necessary to study spatial variability of the soil on both plantations. In many fields, at least of glacial or alluvial origin the soil may change considerably within few meters. May be this soil is more uniform (Vertisol?) but certainly it would be better to check it, at least by making augerings in the corners and in the middle?

Anoop:

Please look at the www.ifas.crec.ufl.edu website for information about Advance citrus production system, but not the CUPS system (covered).  this is from the work of Dr. Arnold Schumann. There is some comparative data about normal and high density spacing and a system for calculating water and nutrient (N) requirements with age and density.  Of course these requirements with age very much depend on soil quality, but no soil has much residual N while P, K and minor elements should be considered on previous results with normal citrus spacing and production programs in the growing area of interest.

Better water management often reduces the fertilizer needs, but close planting accelerates canopy development for the first few years increasing need by age.  More importantly fruit removal of nutrients needs to be compensated for.  This is a larger need in earlier years as yield per area is much higher than conventional spacing. 

Unless lower vigor, smaller final tree size, adjustment in rootstocks is accomplished, trees soon outgrow their spacing and yields quickly level off or more likely decline, again reducing the need for higher fertilizer rates.I hope some of these ideas are useful to your discussion.

Gene Albrigo

Fertilizer requirements for a given cropping system in this case in connection with high plant population density should determined on the basis of the followings: (i) natural fertility of the soil as determined through nutrient omission trials (NOT), (ii) the recovery fraction and the internal use efficiency and (iii) the target yield.  All these information should be gathered on a site-specific basis.

Let us know , how to calculate the doses of fertilizers . Is it on per plant basis or per hectare basis , or canopy volume is to be used , in case orchard is already established.

When you grow plants in high density, definitely total nutrients requirements will increase. It is better to determine fresh requirements when you are going to change the plant density. However, one fact to be remembered is that under increased density beyond a limit, other factors will also be operative e.g competition for light, shade effect at different times of the day, light orientation and photosynthesis etc. Hence, yield will be affected by these factors as well and not only nutrients. This will be invisible factor affecting the results. 

Thanks Nazir. I am talking of the conditions where there is already the optimum density of plant  either on hectare basis or on the basis of plant-to-plant and row-to-row  well worked out . I am willing to know that if our optimum fertilizer requirement is 250kg/ha  under conventional spacing  of 6mx6m ,  what would be the  N dose on per tree basis  when a spacing of 3mx3m is adopted. And the underlying principle to be applied under  two such  contrasting conditions.

This is an interesting discussion. I agree with everyone as there are different considerations we have in recommending fertilizer dose to crops. There are few other considerations one may have to look into, in addition to above facts. Among those, there is a physiological significance on this issue too.

With the high density planting mentioned - I have no idea what the plant density mentioned by Anoop is? - the volume of space occupied by each plant, regardless of the crop, gradually decreases. This can go on until the canopy of each plant begins to overlap and share resources, particularly the solar radiation. Then plant or tree height (vertical growth) will begin to increase. On the other side, root competition from the neighboring plants will push roots to grow deeper, provided that soil porosity is favorable for gas exchange around deep-grown roots. These two situations open up plants for two different environments, and the latter makes the roots to explore deep soil profiles and establish access to nutrients and water.

There may be high fruit set per hectare due to increased plant density, but if all fruits are left on each tree, either fruit size may be reduced (making smaller or too small fruits - so the market may reject due to smaller size) or many of them may be dropped off over time. The decisive factor in this case is the limitation of assimilates and hormonal influence. Therefore, grower should plan to manage the fruit size with the canopy size management or fruit thinning or both. Growing tall will also provide additional fruit bearing potential, but this would be limited due to low assimilation supply per fruit. Therefore, the grower should look into the fruit size and consumer preference. Therefore, we need to decide on the optimum plant size and the density (number of plants/ha) that gives satisfactory fruit yield with acceptable fruit size.

We have got to understand what and how much nutrients are needed at each growth stage. This soil volume should provide all the nutrients and water needs of the crop. We should make sure that the nutrient requirement of the plant is satisfied depending upon the growth stage to fulfill plants’ need. This should be based on quantity required by the plant + nutrients removed by fruits + quantity fixed in soil + quantity leached down + quantity lost by other means.

Expected yield has to be taken into consideration, but heavy fertilization would not raise yields so much. This works around the sufficiency of nutrients (to be above deficiency level) and before excessive level (just for safety of not limiting nutrients), and there is a potential to raise yield to some extent. We should supply this requirement to each of the tree or plant and considering the ability to take up.

Although we work on the basis of land area to be better utilized with the optimum density, the calculation could be made on per plant basis for reasonably spaced crop. But for a densely planted crop, per hectare based calculation is preferred. Other relevant information has been discussed by others in this communication.

Thanks Senaratne , you have added some affirmative dimensions to this whole discussion . Now the question is what about the rhizosphere zone enacted upon by every crop . For example , a fruit crop under 6mx6m versus 3mx3m, under which spacing  , fertilizer doses will be higher on per hectare basis. Do you give some consideration to  fertility  of  soil to lesser fertile soil . That means  , the exploitation of rhizosphere soil with regard to available supply of nutrients  plays a pivotal role in deciding the fertilizer doses , irrespective of criterion used  for  such calculation .

As you mentioned Anoop, once the fertilizer or the nutrient requirement of the crop is decided, then you can simply use the equation we use to calculate fertilizer requirement, i.e. Fertilizer Nutrient (N) requirement = [N(crop) - N(soil)]/FUE. N(soil) is the quantity of nutrient required by the crop; N(soil) is the quantity of Nutrient available for the crop from the soil; the difference between these two is the balance nutrient requirement required to apply from fertilizers; and FUE is the Fertilizer Use efficiency.

There is another consideration one can think of. Assume a farmer is applying water by drip irrigation. He does not need to make the whole land wet, if the crop or trees are planted at a wider spacing. Then you can supply the water requirement of the crop to the effective root zone, so that losses of water could be minimized, and water use efficiency could be improved. Similarly, the nutrient requirement of a plant could also be provided to the area around the tree having good root activities, so that the plant will be able to take up as much as possible. In this sense, no matter whether the crop is planted at 3m x3m or 6m x 6m. It is the per plant requirement of fertilizers you will be supplying to the crop.

You may be able to estimate the total nutrients and the quantity available of each nutrient from the whole land in the root zone. But you may not be able to manipulate to uptake all such nutrients by your crop. May be other factors such as soil compactness, heavy soil texture, stoniness in some locations, etc. may hinder uniform root development to each and every area of the land or in the plot. The nutrient mobility in the soil by mass flow and diffusion may help some nutrients to reach the root surface, but P, Ca, Mg, etc. may not follow that method. Therefore, although there are some nutrients in the soil, some of these nutrients may remain unutilized. In order to ensure better root uptake of applied nutrients, you can apply around the trees where the active root system is found. If the crop is grown with a close spacing and high density, then broadcasting or band application would be the best way. 

The optimum density of plantation should be decided by the optimum photosynthetic efficiency of the crop in question. These two factors are inversely proportional to each other. Whereas, it is not a problem to fertilize the soil on area basis. For instance, for horticultural crops such as mango, citrus, area of the basin surrounding the tree is considered for fertilization, thus covering the total area of the plantation, excluding the interspace as to reduce the total fertilizer

Agree. 

Good suggestion by Senaratne, which can be helpfu.

We will supplying nutrient on per plant basis, that's fair enough . Amount of nutrient , you will be fertilizing will surely vary depending upon the canopy volume , as a function of inter-plant spacing as one of the variants. So ,obviously when you plant at wider spacing , plant canopy would be much higher , and hence nutrient requirement will also proportionately increase. Then , the most important factor we letting off , is the utilisation of inherent fertility present within the  root volume of every plant .

Optimum plant density is a function of  predominantly the photosynthetic efficiency , there is no second opinion. And this photosynthetic efficiency ( Synonymously called as physiological efficiency ) is translated well through the orchard productivity vis-a-vis orchard efficiency , what is popularly known as agronomic efficiency /partial factor productivity. You take any agronomic or physiological efficiency parameter ,optimum planting density should provide a distinct increase in orchard productivity , without incurring any nutrient mining in nutrient profile of soil .  

This is such a relation where we have such conflicting information. Still we do not have in a solid information either to accept or to refute such relation especially  perennial  crops. 

what is observed in small plot when extra polated to large area doesnt hold always true needs verification does it really going to produce more yield may need more but not necessary proportionately as we observed in bt other cottons

Thats the point Dr Ambati..

I've been studying this problem in depth in South Africa for some time now. 

grain yield per dry land maize plant reduces as plant density increases. with a population of 22000 plants per hectare, i consistanly find a grain yield per plant of around 142 grams irrespective of cultivar, location or rainfall. i believe that the similar result has more to do with genetic potential than anything else. 

when plant density decreases, grain yield per plant increases slightly where at 9000 plants/ ha, we get around 190 grams of grain yield per plant. Again this is a very predictable trend. 

I'm currently studying the nutriemt uptake per plant, and this has shown that the fertilizer used in general is in fact very ineffecient. it seems that up to 85% of the applied fertilizer is not taken up by maize plants, and that maize plants in general use very little N, P & K when compared to commonly held views locally. 

It seems that historic fertilizer recommendations is based on taking the very inneficient fertilizer uptake into account, and not on actual plant uptake. My feeling is that more research has to be done, in order to create a more efficient fertilizer recommendation based on actual.plant uptake/requirements and not on a kg/ha basis which tends to ignore planting density. 

I'll be happy to find more info in this regard if available. 

In the case tree crops. I strongly agreed that adequate knowledge of root movement, topography of the land and variety to be planted are highly required

This is issue is more complex in perennial crops than annual crops.And I agree with my learned colleagues , more research is needed keeping an eye on the relation between canopy volume as root volume increasing annually over space and time ?. How does such relation guide fertilizer requirement .?

In the case of  tree crops i think that the fertilizer requirement depend on individual tree requirement  multiplied with  trees number per area unit.

Thanks Dr Ali  for the response. Infact , the major issue lies in contemplating the fertilizer requirement of tree crops with advancing age ..?

In general, the requirement for mineral fertilization in monocultures is calculated according to:

1. Nutrient content in soil;

2. Nutrient content in the plant;

3. Rate of export of nutrients by culture;

4. Soil management (rotation of crops between production cycles, for example, rotation with leguminous species and green fertilization, in this case, there will certainly be lower N-inorganic demand from mineral fertilizers).

5. The rate of export nutrient is higher for crops that have high plant density per area, so replenishment via fertilization is required in a shorter time interval.

Dr. Adijailton,   Thanks for your good contributions.  Are these considerations applicable to  foliar nitrogen application?

Hello Dr. Donwell Kamalongo,

I'm going to answer your question with another question:

Is nitriding absorption more efficient via leaves?

Nitrogen plant nutrition is known to be more efficient via root absorption or biological N2 fixation through symbiotic microorganisms (e.g. rhizobia) or endophytic microorganisms.

Dr. Adijailton,

Your is response is well explanatory. My sincerely thanks.

It is an interesting discussion about a complex topic. Most of the aspects have been already discussed, however I think that we also have to have in mind the crop in question. It is a different thing to talk about trees and perennial plants than annual species. Even more, there are differences between plant species in the way they cope to light and weed competition and their photosynthetic capacity (C3 or C4 plants).

An other perspective is market requirements. Higher plant density usually decrease the size of the final product which can be preferable or not (fruit, leafy vegetables, baby products); therefore this is another factor that has to be considered for plant density.

Weeds also consume nutrients, therefore in order to have a thorough approach one has to try different plant densities and apart from soil and plant nutrients content to evaluate nutrient contents in weeds also. 

A good approach woul be to conduct multi-year experiments with different plant densities and nutrient rates and :

a) measure soil nutrients content at starting point, as well as at the end of each growing season,

b) take samples of plants at different growth stages to evaluate nutrient uptake,

c) measure photosynthetic capacity at various light intensity levels to evaluate the genetic potential of the plant,

d) apply a very strict weed control management or collect all weeds and estimate their nutrient uptake

In any case, there must be a compromise between the optimum nutrient application and the optimum yield in a cost effective manner. Usually, as soon as you reach the 85-90% of yield, the extra yield (10-15%) is very expensive to achieve and does not worth it the extra nutrients amounts. 

In the exercise of increasing plant density the plant to plant crop competition can have the effect of reducing or dwarfing the root system of the individual plant. The response to fertilizer nutrient will be inversely related to the root system of the crop plant on the individual basis. In the closely spaced plantings, the role of input nutrient will increase because the ability of the plants to acquire from the soil will decrease. The secret of the success of SRI rice is the use of early planting before the transplants are root bound, the use of equidistant spacing wider than conventionally recommended, strategic use of an organic amendment to stimulate root development and meticulous weeding. All of these will stimulate a greater development of aggressive rooting. As such the comparative need for input nutrient will decrease in the sense that the soil and root systems can provide for the crop needs.  The interaction of distance and nutrient need would need to determined experimentally for each location and the nutrient need would also be a function of soil fertility at the particular site or sites. 

That is good idea. I think fertilizer requirement depends factors such as type of crop as it governs canopy cover as you said, critical nutrient need of the plant, soil fertility status, fertilizer application technique, and fertilizer use efficiency. For closed canopy annual crops, we broadcast the fertilizer and thus the whole area of cultivated land is considered in addition to the aforementioned factors. For perennial and other plants having relatively wider spacing, area of canopy cover of the plant may be considered in addition to the aforementioned factors again. theoretically, calculation of fertilizer requirement depends even on many other factors that affect nutrient use efficiency of the plant. Practically, however, fertilizer requirement can be calculated as a function of key factors considered above.

In forest plantations, the dose of a nutrient to be applied may be determined as a function of the present foliar concentration of such a nutrient, the foliar critical concentration of that nutrient, the use efficiency for the nutrient, and the crop biomass (mainly foliar, but biomass of other organs may also be considered).  Nutrient use efficiency increases as factors contributing to nutrient loss are reduced.  Conversely, presence of weeds, excessive rain (nutrient leaching), sandy soil, etc, will promote nutrient loss. In fact, in closer spacings few weeds are present and we can spread the fertilizer material around the whole área. However, when spacing is wide localized application should produce better results.

Sir It is always misleading to express fertilizer requirement of widely spaced crops in kg per ha/acre. It should always be expressed on per tree basis. In high density plantations, we consider all plants as single unit growing on a given piece of land. In this case, fertilizer recommendagion in terms of kg/ha or kg/ acre is fine. Therefore, fertilizer recommendation in both the cases may be same since gross canopy cover in both cases is same. The only difference lies in the method of application. 

        Alternatevely, we can compute the difference in yields and accordingly made  adjustments in fertilizer recommendations. 

I think , late statement holds more promise . Why am i saying this , since annual  canopy increment will not be linear while plotting against tree age, this is  one  issue.. ..and the second issue is , you have two comparable inter-plant spacings , one having 300 plants /ha and another having 600 plants /ha , how will fertilizer requirement  on per plant basis  or per ha , vary...? Earlier Paul  Hepperly opine d, it is a researchable issue..? this is surely a researchable issue ..?. 

The use of 300 plants and 600 plants per hectare is given a 0 0 0 no fertilizer, 50 50 50 and 100 100 100 and 200 200 200 fertilizer level on an annual basis. This will produce 2 response curves at the 2 densities. Using this factorial experimentation you can predict a response which will give the best response economically which will be optimium concern for producers. This will take a long term experimentation and focus to do properly. 

Exactly , this is what i am saying  . Such attempts in the past has been distinctively missing , atleast in perennial crops..We cannot say fertilizer requirement with any certainity , especially for high density planting ...  

We could with that kind of experiment. I like that type of experiment with a regional uniform trial basis is the way to get the specific situation and the interaction with local conditions. 

Well said Paul, this is a must to consider , since native soil fertility will surely dictate the magnitude of crop response  , and in the long run as well...

Respected Sir

It may be calculated by following formulae 

(Nutrient requirement of plant-availability of nutrient in soil for plant) X total number of plants.

In case of fertigation, the nutrient requirement will be calculated on the basis of particular plant and its spreading area.

In case of horticulture crop standard recommendation  crop wise per plant should be followed  and under high density crop 4m X4 m less fertilizer may be required per plant  compare to 6X6 m  (plant to plant and row to row) .Fertilizer requirement crop wise may be very with the soil condition,season . In case of acid soil pH below 5.0 liming  at least @2.5 tons per hectare may be applied in the rainy season to make the soil pH near neutral (6 to 6.5) and in saline and  alkali soil  to bring the soil pH between  7 to 8  gypsum may be applied @ 2,5 to 5 per hectare in basin in the rainy season for better nutrient availability in soil -plant root zone. Normal pH  for nutrient availability and microorganisms better function in soil  to plant generally 6 to 8.

good question

we need to look on the input and output, input will consider the level of nutrient in the soil, moisture content distribution in the plot, active root system. output is the biomass that produced in the plot (roots, canopy, fruit). if we increased the plant density by reducing the trees spaching, we may use the water and the nutrient in a more efficient way if we keep enough moisture in the soil, mainly beacause we create a more root mass that delivered the water and nutrient to a smaller distance, we also may produce more yield (if we get enough energy (sun radiation) so for the same nutrient level on area basis, we get more yield (higher nutrient and irrigation efficiency).

Standard recommended dose for particular crop in high density crop per unit are like per hectare. Calculation of fertilizer dose per plant may be calculated on the basis of land area cover by per plant  calculated from plant to plant and row to row distance in squire meter . One hectare area = 10 thousand squire meter  . So, for crop wise squire meter requirement may be calculated from standard  fertilizer requirement per unit area for particular crop.  

Yes, the view point of Karan is OK.

Thank you  Nazir  Hussain for acceptance of my answer for  calculation  of  fertilizer requirement per pant.  

Some of the factors which will change nutrient availability are moisture in the soil, soil organic matter level, nutrient levels in the soil, soil pH, weed competition levels, plant genotypes, the disease levels of plants, and the crop spacing. These are not a comprehensive listing but these 8 areas and their interactions contribute to the complexity of the issue. I believe the best approach is to rank the factors and address them from the aspect of minumum suitable levels. This will provide economic solutions and reduce unnecessary application. As an example in acid soil tropics a suitable pH would 5.7 not 7.0. In alkaline soils 7.3 would be target and not 7.0. In terms of soil organic matter the goal can be a long term one as it takes time to build soil organic matter levels. Since the mechanism of weed competition is related to insufficiency as the levels of soil characters are improved the crops suffer less loss and tolerate weeds more. The ability to widen our spacings and select crops with more agressive root systems will lessen the input need for an optimized yield. Since most recommendations have some influence from input producers they tend to favor high populations and high inputs which are not always favorable for producers especially those who have less capitalization of their operations.  

The explanations of Paul are useful and can help to understand the phenomena.

Nutrient use efficiency of applied fertilizer in horticulture crop like nutrient applied as 100% organic fertilizer, 100% synthetic inorganic fertilizer, 50% organic fertilizer + 50% synthetic inorganic fertilizer application in horticulture garden . The amount of fertilizer nutrient may be vary in per per unit area of crop land according to source of fertilizer nutrient. This may be calculated on the basis of observation of fertilizer use efficiency in relation to response of crop.

you can see this file

Ali, you have uploaded good pdf

I have already mentioned in my previous discussion fertiliser application for high density crop .Please follow these discussion.