Yes interplant spacing dictates the both water and nutrient use where root properties conditioned by plant geometry holds an important role.

See the good paper attached.

http://www.sciencedirect.com/science/article/pii/S2214514113000123

Sir,

The  Roots not only compete for nutrients but also inhibit each other, which ever is stronger and bigger will suppress the other.  Soil type and fertility decides the spacing to be followed. Finer soils and fertile soils may be followed with wider spacing to allow plant growth.  Sandy soils and poor soils may be followed with narrow spacing.  High density planting in such soils (poor) with supply of nutrients is more feasible.  Wider planting in fertile soils is a must.   Water requirement is dependent on evapo-transpiration in the field:

A method used for estimating evapo-transpiration of water by

irrigated crops is the crop coefficient multiplied by reference

evapo-transpiration i.e., ETc = Kc x ETo.  Reference evapo-transpiration

(ETo) is computed for a reference crop using weather data. To estimate crop evapo-transpiration (ETc) the ET0 is then multiplied by an experimentally derived empirical crop coefficient (Kc) . The crop coefficient is worked out as the ratio of ETc from any specific crop to some reference ET (ETo).

The reference evapotranspiration represent the mean value of pan

expenditure in mm/day, over a period for the week which can be

calculated by;

ETo (mm/day) – Kpan + Epan

Where:

ETo=Reference crop evapotranspiration in mm/day over period

          for the week

Epan= Pan evaporation in mm/day

Kpan=Pan Coefficient

Use bell shaped ETc during crop growth

High density require high nutrient dose.  Per plant nutrient uptake has to be taken for calculation of nutrient need.

Even an ordinary gardener like me has learned from my parents that when we plant corn or long beans or other vegetables, we must space out the seedlings.  After the seedlings have achieved a certain size, we may further remove some to space out the plants so that there is space for lateral roots to grow unhindered.  Science research confirms the wisdom of our parents, our folks.

From Subhash's good link: "Compared to normal plant spacing, narrow plant spacing generated less root biomass in the 0–20 cm zone under both N rates, slight reductions of dry root weight in the 20–40 cm and 40–70 cm zones at the mid-grain filling stage, and slight variation of dry root weights in the 70–100 cm zone during the whole growth period. Narrow plant spacing decreased root reductive activity in all root zones, especially at the grain-filling stage. Grain yield and above-ground biomass were 5.0% and 8.4% lower in the narrow plant spacing than with normal plant spacing, although narrow plant spacing significantly increased N harvest index and N use efficiency in both grain yield and biomass, and higher N translocation rates from vegetative organs. These results indicate that the reductive activity of maize roots in all soil layers and dry weights of shallow roots were significantly decreased under narrow plant spacing conditions, resulting in lower root biomass and yield reduction at maturity."

Dr Rajakumar I appreciate your excellent response. We often remain in dilemma, whether we should opt wider spacing or closer spacing on fertile and fine textured soils. We can exploit much better on fertile and fine textured soils using closer planting to allow better exploitation of natural resources.

My response is addressed to Miranda. How do you suggest the criteria to be used while selecting a suitable crop under close planting. Do you feel such criteria will be different from annual crops to perennial crops.

Located in the northern territory of China, the vast semiarid and subhumid regions referred to as dryland areas are stressed by two major constraints for crop production: shortage of water supply and deficiency of nutrients in soil. Low precipitation and its uneven distribution have resulted in soil water, surface water and groundwater deficit, and made crops being under water stress in most cases. As a direct result, except for a few places that can conduct irrigation, most regions remain rainfed agriculture. In addition to shortage of water supply, serious wind and water erosion derived from sparse vegetation coverage, windy climate and frequent rainstorms plus human activities have led to serious soil degradation and nutrient stress. Deficiency of N can be found everywhere and that of P occurs at least in one third of the arable lands, this leading to low productivity. However, the limited water resources have not been fully used and the nutrient use efficiency by crops is very low, both having a certain potential for use and a large room for improvement. Management of water and nutrients are extremely important not only for crop production, but for environmental concern in these areas. Water and nutrients have great interactions that may gain either positive or negative effects on crop production, depending on crop growth stages, amounts, combinations and balance. In the dryland areas, the effect of nutrients and that of water are often limited to each other. Remarkable variations in precipitation from year to year significantly influence soil water and nutrient status, and so do the nutrient input effect. Nutrient input may obtain a good harvest in one year while a poor harvest in another. Considering the precipitation changes and taking effective measures to regulate nutrient supply, crops may not suffer from water limitation in a dry year and from nutrient deficiency in a wet year, and in this way we cannot lose the opportunity to obtain good harvest in both dry and wet year. Nutrient input is the key for crop production. Roots are essential for taking up water and nutrients to support crop growth, and the significance of roots becomes even more important on drylands, since the topsoil is often dry and nutrients are often unavailable, and plants need to extend their roots into deep layer to obtain available nutrients in the moist soil. It has been found that in most cases, crop yield is highly correlated with crop root mass almost in a linear shape. Addition of organic fertilizers can enhance soil organic matter, raise soil water storage capacity, reduce soil bulk density, and therefore create good conditions for root penetration into deep layer. Both organic and chemical fertilizer can provide nutrients for forming strong root system and for roots having a higher capacity to absorb nutrients and water, improve root activities such as raising the root synthetic ability of amino acids by rational N fertilization. Different nutrients have different functions on root growth and its distribution. Nutrient input is also essential for improvement of plant physiological activities. Regulating plant water status and osmotic pressure, increasing the activity of nitrate reductase in plant leaves and raising photosynthesis and transpiration intensity whereas decreasing evaporation constitute some important aspects. All these benefit plants in optimization of the use efficiency of water and nutrients. Experimental results show that the osmotic regulation effect is higher with fertilization. The increase of N-supply level reduces disorder of N metabolism in plants deficient in water and increases plant resistance to drought. Under water stress, rational N supply could make wheat leaves to have high activity of nitrate reductase, high levels of proteins, and better water status. Bleeding sap amount increase per plant by N fertilization provides evidence that water intake by plants is increased. Addition of K can make leaf stomata quickly closed under dry and hot wind conditions. With normal water supply, transpiration rate is increased by fertilization while reduced in a water deficit case. Due to vigorous growth, rapid leaf emergency, large leaf area and high coverage rate of plants on the ground with fertilization, soil surface evaporation is reduced and more water is used by transpiration. It has been found that by rational N fertilization, the ratio of water lost by transpiration to that by evapotranspiration was increased from 0.32 to 0.65, and water loss by evaporation was decreased by 1/3, the water use efficiency (WUE) for both grain and dry matter production being increased. Addition of nutrients, particularly K, can increase chlorophyll, protect the photosynthetic organs from dryness and make the photosynthetic organs fully played their role, and therefore increase the photosynthesis that is regarded as the main cause for crop yield reduction under dry conditions. All these have made the dryland crop production increased. Wise input of fertilizer and manure may do more to prevent soil erosion than some of the more obvious mechanical means of control, since the growing of bumper crops by fertilization not only gives a maximum ground cover but supplies sufficient organic matter to aid in the maintenance of all important soil constituents; and the increase of soil permeability to water under such conditions is certainly a factor of major importance. Effective water management can increase nutrient availability, transformation of nutrients in soil or from fertilizers. Mineralization of organic N is proportional to soil water, and the net mineralized nitrate-N is increased with the increase of water content in an adequate range under suitable temperature. A very closely linear relationship has been found between water content and mineralized N. Due mainly to good aeration induced by deficit of water on drylands, ammonium-N both from soil and fertilizers can be quickly nitrified into nitrate-N. Thus, a large amount of nitrate-N often accumulates in soil profile that has been used as a good index for reflecting soil N-supplying capacity. Adequate water content can promote nitrification of ammonium N while the process is inhibited when moisture content is too high or too low. Water influences mineral nutrient movement from soil to roots and then from roots to aboveground parts of plants. The difference of nitrate N concentrations at different distance points of soil from a plant being greatly declined by adequate irrigation is a typical example showing that some nutrients could be transferred as solute to plant roots with water movement. Adequate soil water content can significantly transfer a large portion of N to aboveground part, and increase N contents in seeds. All in all, water promotes total nutrient uptake by plants and nutrient use efficiency, and affects nutrient composition of plants. It has been reported that N recovery was increased about 20% at any N rate by an adequate supply of water. Water deficit, on the other hand, not only causes water stress to plants, inhibits plant root growth, reduces roots-absorbing area and capacity, increases the viscosity of sap in hadromestome, and thereby decreases nutrient transfer, but also reduces the availability of soil nutrients, nutrient movement in soil, and nutrient uptake and efficiency. Plant growth and crop yield are thus reduced. However, the reduction rate of plant growth is more serious than nutrient uptake, leading to a relative increase in nutrient concentration. Too much supply of water may cause nitrate N leaching and decrease N recovery. Since water supply and nutrient efficiency are closely related, balanced application of nutrients, and determination of their types, ratios, amounts, timing and methods should be based not only on the nutrient-supplying capacity, but also on water status of soil. Rational combinative supply of water and nutrients can increase efficiency of both and produce good interaction. When available water supply is less than a certain range, crops may have little response to fertilizers at any rate, and with sufficient supply of water, nutrient efficiency is increased. An intense interaction exists between available water and fertilizer, and one being changed will likewise lead to the change of the other. The interaction of water and fertilizer is time dependant, and application of water and fertilizer at different stages of plant growth may produce different interaction effects. Oversupply of either or both may delay crop maturation by encouraging excessive vegetative growth, while deficit of water may result in high nutrient concentration in soil, making it difficult for crops to take up and use both water and nutrients, and in a worst case, plants may die resulting in "haying off" effect. The different results obtained for the optimal time of application of water and fertilizer may relate to soil water and nutrient supply at different time. For promotion of water and nutrient fully playing their role and realization of maximum yield, high quality and high efficiency, while protection of the environment from fertilizer ill impact, one important thing is to fully understand and utilize their positive interaction, and attention should be paid not only to input of water and nutrients, but to their rational combination. That is, for addition of water, one should consider nutrient supply, and for addition of nutrients, one should consider water coordination, so that limited nutrient and water can produce optimum effect. Short supply of fresh water and fertilizer pollution has promoted investigations into the interaction effects of water and nutrients on crop yield and nutrient efficiency and WUE, and some achievements have been made. However, there still exist a large number of issues that need further studies in the future.

http://www.agr.gc.ca/eng/abstract/?id=15421000000385

 In a simple way, if the space between plants increased the nutrient uptake increase and the root distribution increased both vertically and horizontally. This is due to that there wasn't any competition between narrow plants on water and nutrient uptake 

Thanks for the excellent responses Drs Kundu , Rajakumar, Deka, Mebarek-Oudina and Mahgoub.  With these responses, I have some onward   quarries :

* In annual crops , do you feel , the competition between the roots for water and nutrients is stage specific or continues along the entire growth period.

* In perennial crops , its ok  , we can work out the fertilizer requirement on per plant basis , but how can we work out the fertilizer requirement in annual crops following the criterion of per plant basis?

* How the reductive ability of the plant roots  is affected physiologically and biochemically?.

Most of the studies revealed substantial  reduction in reductive ability of roots irrespective of perennial or annual crops under high density planting or narrow plant to plant distance.

Sir,

In annual crops or seasonal crops, the competition for water will be continuous and for nutrients it will be stage specific.

Fertilizer requirement in annual crops must be based on nutrient uptake (%) and biomass per unit area. SSNM can be used for separate recommendation for a soil type in an area.

I do agree with you Dr Rajakumar. I will appreciate if you can throw some lights whether or not,  the nutrient requirement of crop , annual or perennial in nature , will undergo some changes as the planting density increases , irrespective of soil . Principally , I am talking . Hope to het back  your response.

In one of the studies in maize , planting density and nitrogen requirement did not modify P,K and s nutrients partitioning to different plant components during vegetative or reproductive periods( except for the N rate effect on leaf versus stem P partitioning )-PDF enclosed

In another study , greater yield of silage can be obtained by increasing corn plant density ( 80000-90000 seeds /ha) without affecting its nutritional composition ( DOI: http://dx.doi.erg/10.311681/jds.2014-8094).

In another study , on planting density impacts on corn and forage yield and nutrient uptake showed at 4.9 seeds per sq  meter , the reduced nutrient uptake was observed compared to seed rate at 8.6 seeds per sq meter , due to reduced biomass and dilution effect of nutrients. ( PDF enclosed)

Necessary PDFs are enclosed for further reading .  

In response to the main question above, it is important to consider that inter-plant spacing is not the only factor affecting nutrient and water use efficiency.

The larger the inter-planting space, the more room for other non-crop plants (weeds) to grow, increasing the competition of the main crops for nutrients and water with the weeds, reducing the nutrient and water use efficiency of the crop and increasing the cost of labor or chemicals to control weeds; more so, at the early stage of the crop.  

Another factor to consider in the nutrient use efficiency, is that the crop demand of more nutrients at different growth stages (in general, the three main stages of an annual crop are sprouting, growth, flowering and fruitification); therefore applying it to early or too late of a given stage, regardless of the inter-pant spacing, will reduce the nutrient use efficiency. This point leads to the concept of the 4Rs of nutrient stewardship to increase [applied] nutrients use efficiency: right source, right dose, right time, right place, which are also factors to consider.

With higher crop-weed competition and poor nutrient use efficiency of the crop, results in poor crop plants development, perhaps weaker plants prone to pests and diseases which reduces the root development and therefore the water use efficiency.

Note that with this comments, I do not intent to response fully to the main question, but perhaps will trigger further discussion to eventually respond to a question with no simple or straightforward answer.

Regards.

Try to read this 

http://link.springer.com/chapter/10.1007/978-90-481-3195-2_17

Very interesting response Porfirio  and   nice useful PDFs Noha , appreciater it . Most of the studies, irrespective of annual or perennial crop , have confirmed higher inter-plant distance allows better growth of weeds , thereby , diverts the water and nutrient use efficiency towards the lower side  and vice-versa. How do you feel , irrespective of planting distance, 4R Nutrient Stewardship   Concept will work or we will have to readjust the timings of nutrient application to match it with nutrient demand. My another concern was , reducing the inter-plant distance will facilitate the better  utilization  of indigenous source of nutrients  reserves in soil , enacted by the much higher root density  within the rhizosphere.  Do you feel keeping different inter-plant distance , there will be some difference in time of crop maturity?

I think Dr Srivastava we must do some researches about this question, we can find the same or different result that the other found 

Porfirio , whats your opinion on these aspects . Let me add another line to already well laid discussion , that such dynamism of inter-plant distance vis-a-vis water /nutrient -use-efficiency  operates quite differently when we compare the  annual crops versus perennial crops.

Sir,

Under high density of planting naturally there will be higher biomass per unit area (not per plant). However the nutrient concentration remains more or less same as that of low plant density where biomass per plant will be higher.  Because of more number of plants and biomass in HDP we get higher nutrient uptake per unit area!

Dr Rajakumar , thanks for response . Besides higher biomass  under HDP , how the nutrient requirement of crops segregate across phonological stages of crop ?. and how the total nutrient requirement varies from annual crop to perennial crops under HDP , is a much bigger question , especially in perennial crops. The inherent soil fertility  is also challenged under HDP , more so in perennial crops?

Do you give any consideration to nature and properties of soil while deciding the inter-plant distance , be it annual crop or perennial crop ?

Under high density planting in perennial crops , there are four components very important in order to realise the  effective use of applied water and nutrients. These are : use of rootstocks, planting system , plant geometry and mechanization . There is absolutely no doubt the selection of rootstock will depend on the nature and properties of the soil . Enclosed below some important PDFs for further reading to have better understanding on the subject .

Problem plants, water and other natural resources is important. There are many examples of inter-related death of plants, animals and humans due to an imbalance in the biosphere.

Dear Anoop,

I understand that my response may not be directly connected to your question but you know better that on any given plant determination of the best spacing is a matter of experiment. If we plant for seed yield we will start losing the seed yield from a density while the biomass still increases. However, from a holistic view which I can see in your question I believe that inter-cropping is the solution. By inter-cropping of compatible species we could reach to combined yields which could not be reached by mono-culture regimes. This is because different species could use different horizons of soil and space so the WUE could reach to higher rates that would never achievable by mono-culture. I believe that we should go towards more complex inter-cropping systems to increase the WUE further as the only way in which we have a still a good chance to progress. We have to consider agricultural systems in which all plant types from different trees to annuals could share the resources in the most effective way. 

My question was to dedicated  analyse the responses from our learned colleagues  , how the interplant distance dictates the plant growth , nutrient and water use efficiency and the nutrient acquisition pattern , in addition to influencing the time of crop maturity . Unfortunately , high density or ultra high density planting in perennial crops , consume so much of the time to arrive at such conclusion . Is there early indicators of such responses to establish the effectiveness of different  plant density levels ? 

Very nice response Kirti . How do you see the C-budgets of the plants in closer spacing than conventional wider inter-plant distance ?  Do you feel ,  plants at closer spacing will require much lesser nutrients compared to plants grown at wider spacings , at equivalent productivity levels? 

Abhishek , how quickly , you gather such pertinent literature , i simply admire you ..

Lets ask Kirti for the  results as given below , read as:

With increasing the nitrogen levels and plant densities,  agronomical nitrogen use efficiency, physiological nitrogen efficiency and nitrogen use efficiency were decreased and apparent recovery nitrogen efficiency was increased. This was in potato 

Anoop Sir,

Normally spacing for annual crops is fixed based on its growth and soil fertility levels.  Based on number of plants per unit area and fertilizer per unit area we can workout the dose per plant. But it will be difficult to apply on per plant basis in annual crops.  The NUE including WUE will be better in populated area than wider spacing. However, the growth will be higher in wider spacing.  Still the yield per unit area will be less here.

Very fascinating responses from both  of you , my dear friends  , Kirti and Rajalumar . both of you adding some thoughts for further discussion . This is the beauty of platform like RG. 

Kirti , thats the reason , utilisation of accumulated nutrients is perhaps more important , in lieu of apparent recovery of applied nutrients . This is what we meant by nutrient efficient genotypes..?. Off course , here we have stronger intervention of spacing ..?

Rajakumar , what exactly decides inter-plant spacing in perennial crops ?. Is it the type of rootstocks that we use ( Vigorous versus dwarf )? . Why do we have to have two different considerations, one for annual crops and another for perennial crops?. Do we consider the nature and properties of soil while deciding the inter-plant spacings?

Iuliana Florentina Gheorghe to you 2 hours ago

The distance between individuals in plant crops must take into account on two things:

- it must be sufficiently close together so the body each plant to achieve a degree of coverage of the soil a hundred percent. Thus plants by their shade prevents water loss through by evapo -transpiration;

- at the same time distance between plants should provide enough space such that solar radiation to be used to maximum by plants, to avoid competition for light and nutrients.

Iuliana

Please see the paper:

Effects of row spacing on soil water and water consumption of winter wheat under irrigated and rainfed conditions

http://www.agriculturejournals.cz/publicFiles/36131.pdf

Anoop Sir,

In perennial plants, we can consider plant height (normally proportion to root penetration into soil depth) and canopy width (normally root spread area) plus some buffer space to decide the number of plants per unit area.  No doubt, the nature of soil particles and the properties will have influence on soil fertility  in-turn the number of plants per unit area.  If we use root stocks which have vigorous growth will spread fast and occupy more space, hence we must have less population per unit area. Where as with dwarf  plants have less root growth and population will be higher.

Dr Rajakumar and Kirti , thanks both of you . My straight concern is , do we consider the soil fertility as one of the factors to decide inter-plant spacing ?.  Kirti , in high density and ultra high density planting , lower yield is ascribed  to failure to trap the solar energy for photosynthesis , especially when plants are matured . LAI , could be one factor , but it is only valid in banana. 

Yes Sir

We recommend less spacing in cotton if soil fertility is poor.  If soil fertility is good cotton can grow and occupy more space hence we advise farmers for wider spacing.

 i appreciate your comments  , Kirti and endorse Rajakumar as well . i was looking from a little different angle . Cant we have some plant-based parameters , capable of expressing at pre-evaluation stage itself , so that when these plants go to the field , they find enough space horizontally and vertically to express themselves unhindered.  for example , root CEC, stomatal density , .... Is there any scope on this angle..? 

*Do you feel inter-plant spacing is dependent on soil properties ?. If so , how will you decide to grow annual or perennial crops using different modules of high density ?

As for this question, we should also consider what kind of the crop we plant, because some like acid condition in subtropical and tropical area, however the others like less acid soil. For example, sweet potato grows in a good condition in the soil which contains high property of sand. Besides, for the same crop, different environment will also affect the quality. For example, due to different photoperiod, the wheat grown in subtropical area is high in starch, while in temperate area they are high in protein.

This is a very question, no straight answer, i put few points

1. spatial variations in soil characters for deciding soil moisture and nutrients availability as a function of soil texture, soil structure, topographic/undulating features and henceforth agronomic and inputs' management

2. Inter-crops and inter-varietal differential response to major inputs as fertilizers and water, and henceforth decision making for row to row and plant to plant spacing and appropriate inputs management

3 tiller compensation in crops under variable crop cover, arising due to plant to plant and row to row architecture

4. Canopy environment modifications and associated micro-environment within the canopy

4. differential response to nutrients inputs under varying moisture levels, and henceforth tuning of the appropriate canopy

5. definitely the recommendations exist for variable water supply situations for agronomic and nutrients management for sustainable production

nice question, Dr Anoop, raises the need of integrating so many factors/attributes and environments

Good points mentioned by Kalra.

Thanks Xiaohui for putting up another good point  , the architecture of the plant , which ocnsiders both above -ground and under-ground architectural developments in tandem , to really decide the inter-plant distance , without affecting either yield or quality . Point well taken , Xiaohuii. 

Some thought provoking points tossed up by  Dr Kalra. These are the points , more directed towards improving then efficiency of applied nutrients and water.  And in a way , if good floor management is substantiated  , could the inter-plant distance be neutralized ..?

Let em raise  another issue , perhaps we did  not get the convincing answer even now.  Our eralier discussion highlighted that soil fertility level is pivotal issue to decide the inter-plant distance . this could be a possibility , but in perennial crops , we simply go by the dwarf or vigor of the rootstock used for different scion of the fruit crops. if we do not know the precise nature of rootstock , especially if they are imported from outside , how to streamline then plant-to-plant and row-to-row distance ..? 

very useful comments by profs and specialists. I can add some few points that distance between plants and rows have impact on yield and growth of plant. the sunlight will not penetrate and plants will try to elongate and much energy will be served in this matter as to be served in flowering and fruiting.

smaller leaf area and more no of leaves will cost much energy.

roots will be in competition for water and nutrients and over all growth will be less as compared to recommended ones.

Very nice feedback Hussain , what will happen to nutrient requirement of a crop on per hectare basis , when you compare two conditions , in one condition , there are 277 plants in one hectare of land having plant-to-palnt  spacing of 6mx6m, while in another  case , there are 1112 plants on a hectare of land with spacing of 3m x3m . how does  N requirement on per hectare basis will vary , considering 500gN per plant as optimum n dose..?

We need to calculate fertilizer requirement either on root volume basis or on canopy volume basis. Inter-plant density will also depend on the soil mineralogy. 

What will happen to total fertilizer requirement when you calculate the fertilizer requirement on hectare basis. do you feel the fertilizer  requirement  will be significantly  higher with inter-plant density of 3x3 m compared 6x6m, what kind of mathematical equations really operate to define such relation , i have yet not found , my dear friends...?

It remains to be seen how nature and properties of soil affect the fertilizer requirement under high density planting ?

Well said Dr Shirgure , i agree with you...

It will be interesting to see whether fertilizer requirement increases or decreases with increase in plant density or reduced inter-plant density.

Yes, a good research can provide an answer.

I agree with you Dr Nazir , this is the area  where  we have absolutely no clue at all , and no clue across different perennial crops, while working different school of thoughts. ..besides no underlying principles of adding RDF as per planting density..

You are right Dr. Kumar.

Dear 

I agree with my colleague Fateh Mebarek-Oudina

regards 

The subject has been well explained by Dr. Raj.

• Any reason to supplement , why high  planting density of crop is associated with reduction in crop nutrient requirement  ...??

Most probably due to reduction in nutrients availability per plant.

I think two different types of mechanisms involved in relation between nutrient acquisition and annual versus perennial crops.

 In perennial crops this is a very touchy issue. We are still not sure that increase in plant age how the nutrient requirement undergo chages at different productivity stages of these perennial tress ?  

Thanks Dr Shirgure and Abhishek for your feedbacks. s far as perennial trees are concerned , very little inroads have so far been made in this regard , especially when plant canopy management comes into picture  . In annuals , the situation is comparatively easier  ..

dear sir

The ideas regarding the set of questions have been conveyed by different scientists in a very nice way.  Thanks all

in this series i would also like to add some points. I worked on sunflower for last 2 years and one of the factor i investigated was planting densities. From my reseach work i would like to share some thing as below:

- increasing plant population decresed root mass density and DMA per plant (including DM partitioning to seed).

* Irrespective of soil status, increasing plant population by 20% did not affected seed yield per unit area basis.

*However, if we wish to further increase the plant population, the performance of crop w.r.t DMA may vary with soil status

* Nutrient requirement under high density planting increases 

Thanks

Thanks Dr Dhillon....

Under high density planting , the inherent soil fertility is put to maximum use , thereby , it cuts down the total nutrient requirement..?

Let us discuss the relation between use of soil fertility and root activity under high density planting, especially using perennial crops ?

Abhishek, very interesting feedback. How do root systems of two plants, annual or perennial in nature, they behave when they overlap with each other and how they impose their effect on soil fertility changes, is a matter of through investigation. 

Dr Shirgure , i am so happy , that you have flagged off this issue, which is so important in the context of whole discussion...

Some latest work...

Productive and physiological performance of lettuce cultivars at different planting densities in the Brazilian Semi-arid region

In regions of high temperature, production and quality in the lettuce is reduced. This requires finding of cultivars that are more adapted to such conditions and adjust the planting density for each cultivar. Consequently, the aim of this study was to evaluate the productive and physiological performance of lettuce cultivars at different planting densities under semi-arid conditions. The experiment was carried out at the Horticulture Teaching Garden of the Federal University of Ceará in Fortaleza, in a randomised block design with four replications, with the treatments arranged in a 4 × 4 factorial scheme. The first factor consisted of four lettuce cultivars (Red Salad Bowl, Salad Bowl Green, Mimosa Green Salad Bowl and Crespa Lollo Bionda) and the second factor of four planting densities (0.20 × 0.20 m, 0.25 × 0.25 m, 0.20 × 0.25 m 0.25 × 0.30 m between plants and rows). The characteristics of the lettuce such as qualitative (age at bolting and flowering, and state of health - pests and diseases), quantitative (plant height and diameter, fresh and dry commercial weight, fresh and dry non-commercial weight, and total fresh and dry weight), and physiological (gas exchange) were evaluated. The Salad Bowl Green and Mimosa Green Salad Bowl cultivars displayed average tolerance to bolting (63 days after sowing, DAS) and late flowering (95 DAS). ‘Salad Bowl Green’ had the highest total fresh and dry weight. For density, greater individual plant production was seen at 0.25 × 0.30 m; greater productivity of commercial fresh weight and total fresh weight was seen at 0.20 × 0.20 m for all cultivars. ‘Salad Bowl Green’ is the most promising for cultivation under semi-arid conditions when grown at lower densities.Source ;Vol. 12(10), pp. 771-779, 9 March, 2017 DOI: 10.5897/AJAR2016.11961A

PDF enclosed for further reading...

http://www.actahort.org/books/1164/1164_36.htm

By spacing plants to accommodate the expected mature size of a plant, ensure plants have enough room to develop a healthy root system and limit competition for access to water and nutrients. As a result, plants are less stressed and more resistant to pest problems. Proper plant spacing allows for air to circulate around the plant; crowded plants are more susceptible to diseases and require excessive pruning. Plants should not need to be pruned more than twice a year. If a plant needs more frequent pruning, it likely doesn't have enough room to grow. Enhancing WUE at the canopy level can be achieved by adopting practices that reduce the soil water evaporation component and divert more water into transpiration which can be through crop residue management, mulching, row spacing, and irrigation. Important factors that affect NUE in a crop production system include weather, water availability, tillage practices, proper plant row spacing, crop rotation, fertilizer rate, timing, placement, and source