<TITLE: Agroforestry in the Tropics and Developing Countries
ACADEMIC DOMAIN: natural sciences
DISCIPLINE: forestry
EVENT TYPE: lecture
FILE ID: ULEC240
NOTES: continued in USEMD290, seminar also includes presentation USEMP140

RECORDING DURATION: 57 min 11 sec

RECORDING DATE: 26.4.2007

NUMBER OF PARTICIPANTS: 10

NUMBER OF SPEAKERS: 6

S1: NATIVE-SPEAKER STATUS: Arabic; ACADEMIC ROLE: junior staff; GENDER: male; AGE: 51-over

S2: NATIVE-SPEAKER STATUS: Arabic; ACADEMIC ROLE: research student; GENDER: female; AGE: 24-30

S3: NATIVE-SPEAKER STATUS: French; ACADEMIC ROLE: masters student; GENDER: female; AGE: 17-23

S4: NATIVE-SPEAKER STATUS: French; ACADEMIC ROLE: masters student; GENDER: female; AGE: 17-23

S5: NATIVE-SPEAKER STATUS: Swedish, Finnish; ACADEMIC ROLE: research student; GENDER: male; AGE: 31-50

S7: NATIVE-SPEAKER STATUS: Arabic; ACADEMIC ROLE: masters student; GENDER: male; AGE: 24-30

SU: unidentified speaker>


<S1> today we are <P:06> having only one only one , one presentation maybe towards the end of the lecture then she can give give us h- her presentation but i will start with , finishing up with the course , remind to you with the importance of the organic matter emphasising that organic matter is quite important for s- soil fertility <P:05> and this is . maintenance of organic matter is one of the core core ideas of the agroforestry and that would be (xx) (through) either below ground root fine root turnover which is quite fast the trees can can can turn their root very fast and then below ground . and normally below ground of trees depending on of course on the density is between three to six megagram per hectare which is quite a lot . a megagram is one million gram is one one thousand so it's three to six tons of root biomass below ground and the turn- turnover especially of the firewood is quite important and that the turnover is the turnover of the organic material , and that is release of nutrients . to the soil a release of nutrients is , either is cellulose <WRITING ON BLACKBOARD> or s- hemicellulose or lignin and plus here is soluble carbohydrates , which the release of which is quite fast , this is from the below ground part . the above ground , we can have intentional , and that also (has part in the) (xx) agroforestry where the (xx) one of them is intensive intentional . the intentional one of the (xx) that you intentionally cut so pruning the branches or bring down the branches to the soil and then through decomposition <WRITING ON BLACKBOARD, P:07> the nutrients are released to the soil and the process of decomposition itself depends on the <P:07> components of the leaves how much soluble carbohydrate how much is cellulose and we see that the rate is decreasing , this from cellulose hemicellulose and the , is slower than decompose in the lignin which is composed (towards) the grow maturity . some of the leaves of course contain polyphenols <WRITING ON BLACKBOARD, P:06> which is high in carbon some of them contains tannins which can bound to the nitrogen of the soil and make it unavailable to the crops the tannin material , th- c- they can combine with nitrogen and make it unavailable to the crops <P:07> and we see we have seen the ratio nitrogen carbon two BS is 110 to one , to two by width in the different components , and this is why the nitrogen carbon ratio is carbon nitrogen ratio (xx) see a ratio is always (very) close or between 12 and ten that is it means the soil is good soil if it is th- if it goes up that means there is quite a lot of carbon when there is quite a lot of carbon also in the soil that means quite much of the nitrogen is fixed to the carbon and becomes unavailable to the crops that means like the decomposing organism would like to build in their bodies by taking much of the nitrogen , from the soil when there is plenty of carbon that means there is quite a lot of building of the bodies of the organis- or- organisms soil organism that means they are using quite a lot of or cons- consuming quite a lot of nitrogen and make it unavailable from the soil to their bodies and you have we told that plants cannot eat life (wells) or life organi- organisms in the soil unless they decompose themself then they release the nitrogen again to the soil <P:06> with the with the pruning there is quite much of the nutrients because we prune and we cut the green leaves so much of the nutrients fall with the with the leaves and there is plenty of cations and anions released but when it comes to the litter fall <WRITING ON BLACKBOARD, P:06> then much of the nutrients would have already taken back to the tree in a process called translocation <WRITING ON BLACKBOARD, P:06> that means that the plant takes the nutrients from the leaves and locate it back . to the plant and the leaves that falls are more or less . not as . nutrient-full as the green one the g- the green one we prune it thus we cut it with all the nutrients and then it falls and decompose and releases quite a lot of nutrients this one the litter fall contains less amount of nutrients , and they leave plenty of of course plenty of lignin plenty of cellulose and <SU> [hemicellulose] </SU> [hemicellulose] <P:07> all this are related to <COUGH> to the organic material of the soil the importance of organic material that means will help in water holding capacity will help in i- releasing of nutrients and also capturing of nutrients from the soil and make them available to the plants <P:05> organic matter improves the soil physical structure the aggregate . of the soil making crops . improves the neutralising of the acidity and salinity of the soil making the PH fairly close to seven . which is neutral . of course excessive addition excessive addition of organic matter like manure or what so ever that will affect negatively the growth of the plant if you add too much organic material , organic matter or manure if you add too much organic material with plenty of <SU> carbon </SU> carbon that means you deprive soil from the nitrogen because the decomposing organism will build in because there is much of carbon added to the soil and the soil will be deprived from nitrogen <P:16> there are different factors that cause the loss of soil organic matter , intensive cropping . that is quite fast decomposition quite fast remover of nutrients and if not captured by the crops or by the plants then much of it will will be lost especially if there is water erosion or wind erosion then much of the nutrients will be dele- wi- will be lost from the system and in agroforestry the good part in agroforestry that we always rely on trees to capture , the nutrients from escaping from the system from go- going down and then bringing them them again to the top and then it's still we can't bring the make the nutrients available to the crops through pruning or they come as litter fall or through fine-root turnover or decay of coarse roots below ground . of course in agroforestry system we don't should not forget the the animal part animal manure if there i- if there are some livestock eating then the animal manure will add to the organic material and then decomposition the the the the organic ma- organic matter and nutrients will be released from the manure and also the urine of the animals will make quite a lot of nitrogen available but if there is much of nitrogen in the urine that probably will affect negatively the growth of trees all across the board of the , if there is much nitrogen that will kill the tree excessive nitrogen <P:06> tillage tillage of organic matter mineralisation will be unavailable so fast decomposition soil erosion will remove , the organic matter and of course crop removal and tree removal tree felling and tree burning in shifting cultivation also will deprive the soil from organic matter so whole tree harvesting is quite dangerous com- also crops just removing every year the whole crop the grain plus the biomass (biological) biomass <P:06> from the soil that would every year would take that means after some time you get would come to the first (xx) and that you have grown (for the shifting cultivation) that would (xx) decline of over years because of removal of the nutrients from the soil in shifting cultivation without addition of synthetic fertilizer in a way or because of the short rotation in the (xx) system and shifting cultivation that would come to the state that , productivity comes almost to zero <P:13> some form of soil damage occur quite frequently in the (marginal) soil where organic matter in fact in the marginal soil is quite low so this is why in the dry-land pretty close to the desert margin the the farmers or people should have to really plan their fields in a way that not to decrease the soil organic matter this is why maybe (pastoralism) , in the desert margin in the typical dry-land where there is (a set of acacias) that would be the best er land used practice in in in that areas otherwise if there is agriculture or farming of or cultivation of agricultural crops then the quite soon the soil will be deprived every year because of the less organic matter less vegetation cover then there is high wind erosion then the yield will be d- the yield decreases year after year <P:05> poor irrigation especially used in in the dry-land quite much of irrigation comes from saline from saline water especially from deep bore wells addition of salt , to the soil will accumulate every year and we have sodic saline or sodic soil <WRITING ON BLACKBOARD, P:05> that's addition of salts is accumulation of <SU> sodium </SU> sodium and we have seen that when sodium becomes more than , f- four , (million) centimole and this is where the rates are 15 , then the soil will be unsuitable for agricultural production , will be saline sodic soil <P:08> and y- you know the equation of (xx) soil sodium percentage or sodium (xx) that is why sodium is quite dangerous even for human being not only for crops but crops soil you know that sodium is one of the main , minerals that contribute towards hypertension in human beings <P:14> so it is not only causing h- hypertension for human beings but it's also damaging the soil causing soil dispersion <WRITING ON BLACKBOARD, P:08> </S1>
<S5> <COUGH> what is this hypertension </S5>
<S1> hypertension </S1>
<S5> yeah </S5>
<S2> it is a high (xx) (of blood) </S2>
<S1> high blood pressure </S1>
<S5> ah okay </S5>
<S1> yes , then like <SU> @@ </SU> so the the the the this this sodium is is is quite dangerous and and it's difficult to remove from the soil either through through drainage and it's very difficult to drain it , of course if it is (multivalent) , and always the (multivalent) is less (xx) and dry and others so because of that it's only one chart then it's difficult to to get rid of the sodium , is easy to get rid of the other ones calcium magnesium but sodium can be released by maybe only by potassium which is also (multivalent) <P:08> and so drainage that is one way but there are some some salt loving plants that you can plant there , that they can take salts including the sodium especially those plants that grow very close to the , salty water or salty soil (xx) is one of them . (xx) see that's species , is one of those species that grow in in more than 33 per cent or thir- 33 salinity it's quite high <P:07> this is , and many many of the plants because of the accumulation of sodium an- they become like unpalatable soil as one (xx) or prosopis is another one many many of the acacias they grow in saline soil but they still they they don't accumulate the salts in their leaves but many of the plants like prosopis accumulate zinc zinc loving and copper , in the leaves and it becomes like a repellent and this is one with adaptation maybe against (xx) and there is (xx) that accumulates kind of toxic minerals in the leaves and it becomes unpalatable to the plant to the animals but by doing that those those plants they remove the toxic material from the soil one of the famous crops is sorghum , for reclamation of saline soil especially if you are pl- if you are in dry-land and you are planting the land for the first time because of the <COUGH> high calcium carbonate . in the top soil there is plenty in the dry-land there is plenty of calcium carbon- if you can just see the surface of the soil is white because of calcium carbonate , and because it's high much of many of the people many of the farmers they start cultivating their land with sorghum plants because it's salt loving and then they can get a harvest and then they completely they harvest the the the the the the sorghum that means they are taking the cal- calcium carbonate from the soil after planting successive three or four years successive successively with sorghum then the soil will be maybe is er (cleared) and that they can't plant other other crops <P:07> er this is part of reclamation of of saline soil one of the causes that cause the damages is shorter rotation , of shifting cultivation , pollution of the soil (adding grey) water is quite a lot of especially that comes from industrial areas that means you are polluting the soil addition of even excessive addition of fertilizer synthetic fertilizer that it means you're adding toxicity to the soil and accumulation of nutrients of nitrogen in the soil it is itself is quite dangerous for the soil , this is why th- w- why the soil gets toxic if if irrigated by grey water because there is quite a lot of toxic material that would come from for example tannins there is quite high per- percentage of tannin material in the water tannin content and tannin is , contains quite a lot of n- of carbon and that means makes , nitrogen unavailable and maybe the soil toxic for crops <P:05> agricultural intensification that is too much , continuous cultivation of the land depriving the soil from from nutrients and at the same time that means excessive irrigation and excessive irrigation either brings the salt up , slowly in (xx) that means raising the water table raising the w- water table and bringing salt upward which means damaging the soil <P:07> this is how er , intensive , agriculture looks like , so either use ploughing , that means enhancing the decomposition of organic material so ploughing , with extensive irrigation and with high trans- high high (evaporation) and with harvesting the crops all-tree h- all-crop harvesting that means depriving the soil from the nutrients with addition of quite a lot of fertilizers and pesticides that is also toxi- toxifying the soil , so all this practice of intensive agriculture with monoculture of agricultural crops started from ploughing people now farmers started to go for no-till no plough less tillage . just to (xx) no-till operations many of the farmers now have this adopted by many to reduce or to help to improve the soil is to go for no-till no tillage , no ploughing to maintain the , soil fertility . no (xx) tillage <P:05> in nutshell those practices of intensification shorter rotation will bring in salinisation will bring in e- erosion will bring in compaction through the heavy machinery that means compaction of the soil that means less (corrosivity) less (corrosive) that means quite a lot of run-off less derivation for crop growth for root development less yield , will bring in dispersal of the soil through accumulation of sodium and crusting of the soil <P:12> example of over- (xx) irrigation excessive irrigation people they don't have the in in mind although this is a research farm , but the research farm of agricultural researchers they they don't have the concept of having of planting trees all what they have studied is planting of sorghum and sesame (xx) even they th- the the the thinking or or the culture of planting trees is not in their minds if if if they if they will have taught in the , in the school that trees can benefit and can create productivity can (xx) climate and things like that then without being taught this is part of the farming system then it's for their own sake , i (xx) someone who come just to the middle of the desert and then start planting and growing agricultural crops without having a single tree just for the landscape it should have to be there but look now not a single tree and this this is has been experimental site for so- some years , and they haven't thought of planting just boundary . fence of trees they just think about agricultural crops and they try to they have tried to to to (xx) and they (xx) the soil by addition of organic matter of course they have some manure and some other fertilizers thus comparing different treatments but they haven't thought of improving micro-climate would add and increase productivity even probably more than nutrients and water in the dry-land is more crucial is more crucial and important than these than nutrients <P:10> the disadvantages of monoculture of agricultural crops , there are many . to list some <P:11> without going into detail of . salinisation excessive irrigation plenty of salt water logging (no agricultural) (xx) then at the same agricultural people they come again and discuss what , the problem that they have caused through . the the the the (xx) practices <P:08> soil erosion very few trees that can grow in such kind of <P:05> <FOREIGN> (xx) </FOREIGN> what is this </S1>
<S7> <FOREIGN> (xx) </FOREIGN> </S7>
<S1> (xx) but i don't think that is <FOREIGN> (xx) </FOREIGN> what is grazed but the (xx) and then (xx) trees of this is meant to be a (xx) and these kind of trees are (xx) than (xx) and this is what the remaining of , (xx) the problem wi- in the dry-land is how to maintain is is how to establish tree . how to establish it there are some local adaptive native trees to establish them around the farm to grew them within the er within agroforestry system and then to manage them well and many of those scattered trees few scattered trees there are they (cope as well) they don't have any problems (xx) they provide fodder they will provide (xx) (walls) firewood so they're quite multipurpose trees , and there are they can fix nitrogen <COUGH> they can protect the surface soil against erosion , and they they can build in organic matter and building in of organic matter is it's quite a slow process you need if you lose it then you need quite a lot and many years to build it back and here bu- building soil erosion can cause lo- loss of nutrients and reducement of holding capacity accounting for 50 per cent (xx) losses in productivity in the US the other year topsoil erosion is about 17.5 tons per hectare per year , quite a lot 17,500 kilograms of top soil and nutrients are in the top soil what you are talking when you are talking about nu- nutrients for agricultural crops in the top soil it is not in the surface in the subsurface the top soil which is the first th- 30 centimetres if you lose this top soil that is you lose the the most nutrient part nu- nutri- nutritious part of the soil and to build in one per cent , which equal 22,500 kilogram 22.5 ton of organic matter in the 15 centimetre depths of top soil , that means <WIPING BLACKBOARD, P:07> if you have a hectare <WIPING BLACKBOARD, P:05> one hectare is 10,000 . <WRITING ON BLACKBOARD> square metres , times 0.15 depth 15 centimetres just to get the volume , area times the depth <P:05> time this is width this is volume time the bulk density this is width time the bulk density because bulk density equal width over volume i want to multiply the volume of this soil per hectare by the bulk density . 1,500 kilograms per metre cube , times one per cent <WRITING ON BLACKBOARD, P:06> this is a soil which contains one per cent organic matter in the top 15 centimetre and it's the rules say that any soil which contains less than , soil is less than two per cent organic matter is a bad soil , the good soil is more than two , up to five . so this soil , if you calculate the whole thing , 15 , 15 times 15 is 2000 225 times 100 kilogram that means 22,500 kilograms of organic matter in one hectare if you want to build one per cent of orga- of organic matter you will need 22,500 22,000 tons of organic matter either animal manure or (xx) you w- you you increase the organic matter in the soil by one per cent if you m- if you want to make it two per cent then times two that is 45 <WRITING ON BLACKBOARD, P:05> tons of organic matter quite a lot so it's always better to manage for not to move the organic material from the soil because it's difficult to replace <P:08> and replace is always either through addition of animal manure or compost or cover crops y- i- you you you cultivate some crops and then you take the the this the grain or whatsoever and then you leave and plough in the soil the remaining of the crop and by doing that you build in gradually the organic matter content of the soil which is important for the previous slide which you have seen for the nutrients for water holding capacity for the structure for against erosion and <P:11> one of the common mistake for taking samples in er just i- in soil in general that because people are fond of this randomisation so many of the people they just prefer go and take random sample of soils which is quite common mistake . in soil you don't need to go and take because you cannot average , (general soil) , you cannot get the average of that if one place is fertile and the other one is infertile if one was plenty of sodium and the other one is has no sodium and (deficient crop) sodium there you cannot make a bulk of soil sample and say yes this is the average for that soil so there is this kind of averaging in in in random sample in the general statistics will not work for soil in soil you need to stratify it and divide your soil according to different criteria according to (xx) material according to topography maybe according to (briefing) of utilisation to history of utilisation to crop yield and then after that the some are high some are low then according to that according to this stratification you take your soil samples when you stratify you can randomise after that after you make the stratification then you can do the randomisation but not before that this is just a rule of thumb , and also for the depths because soil also can vary in the depths it is not only the surface soil but the subsoil and you have seen in some of the lectures the not only (xx) soil (over the s- subsurface for) or surface soil but also making a soil (properly) is quite important to see this the development of the soil . soil erosion <P:05> few words about nitrogen and how nitrogen could either g- go- go both both ways either in mineralisation to be available for the plants or can go the other way and assimilate and be bound to the body of the organic m- of the organism or bound organic matter and becomes unavailable and there is nitrogen fixing and it's always better for agroforestry for trees to be a nitrogen fixing tree to the add to add to the nit- nitrogen in the soil to avoid using fertilizer and you have seen from (xx) bush how <WRITING ON BLACKBOARD, P:10> how the organic how production of methane use of methane that could produce carbon dioxide and t- to use the hydrogen , to use the hydrogen for <WRITING ON BLACKBOARD, P:05> for making (xx) for (xx) fertilizer and you have seen that contribute quite a lot of carbon dioxide for climate change so this is one of the bad effects of <SIC> fertilisation </SIC> making fertilizer producing since synthetic fertilizer is quite damaging to the environment , from this start from the start of production (xx) that comes to the soil then it has if this is successive then it introduces toxicity of the soil toxicity of the of the water <P:09> and this nitrogen (succession) there are different rhizobia different bacteria that can live in symbiotic association they take the carbon from the trees so nodulation nodules , and they fix the nitrogen in the nodules and the wood nodule is pink in colour . that means the nodule is effective and infective infective means bacteria and effective affec- infective and effective that means because th- there are many different genera of bacteria that could nodulate different trees and some trees are obligate some trees are facultative that either they nodulated by only species or one genus or they can take many and those different species of bacteria that are in the soil some of those general species are not ef- they can infect they can go to the nodules but they are not effective in making the nodulation , in in biological nitrogen fixation so the the right choice if you are doing inoculation if you are adding bacteria to the soil or to to see these then look for effective infective strain of bacteria that makes good association with the tree , quite a number of species that are th- numerous trees they can grow in places where there is no bacteria they will not make nodules but similarly if you grow them in a place where the the the a the present bacteria is not effective infective r- right one they can make nodule but not that producing quite enough , fixing quite enough nitrogen and this as- this association must be like symbiotic it it s- gives give and take it gives nitrogen to the plant and it takes carbohydrate it takes carbon from from from the tree if the nodule is not effective then it becomes like one way they take from the tree without giving much or fixing much of the (volume) of the atmospheric nitrogen <P:05> and many of those like , fas- fast growing especially the mesorhizobium and sinorhizobium they're fast growing bacteria that they can nodulate many of the acacias , effectively making effective and infective nodulation with many of the acacias and prosopis bradyrhizobium is a slow growing it can nodulate acacias but not very effective it is very effective inoculating with herbia albida and this is one of the differences between the herbia albida and the acacias with herbia albi- albida herbia it was with acacias and for some differences has been taken from the (xx) acacia and (xx) herbia and one of those differences that are nodulated bacteria of (xx) herbia is not the same as nodulating bacteria of the genus acacia this is one of the differences beside there are so many other taxonomic i think differences , so be careful with nod- because just just bacteria can can really build in quite a lot of nitrogen and even in some trees you can get five 500 kilograms per hectare which is quite a lot and that probably is more than enough because quite often people they use 50 kilograms per hectare or maximum 100 of synthetic fertilizer and just through biological nitrogen fixation you can get you can build in about 500 , which is quite (xx) that is safe , and you know that there is plenty of nitrogen in the air 70 to 90 per cent or 80 per cent of atmosphere is nitrogen and over each hectare or over each hectare there is 6,100 kilograms of nitrogen so it's free then the bacteria get it put it to the soil that could be good for the symbiotic associations and it's good for the forestry <P:09> erm i won't say anything just for the lack of time i want to save some time for the next speaker , at least i've tried to get some nodules in the field and it seems that it's difficult to find but this is also acacia seminar (i'll examine) the soil and during the (xx) the the the environment are conducive for the nodulation but in spite of that , we couldn't find th- the nodules maybe for one reason or the other one reason could be that the , there is no strain of bacteria for nodulation one reason the other reason could be there is enough nitrogen in the soil where there is plenty of nitrogen then there is no bacteria there no bacteria strain an- when there is plenty and then probably also there's nodu- nodules but they are deep in the soil because we just scratched the first top one metre we <SIC> digged </SIC> about one metre and then we didn't find it but probably down there like there's (xx) four or five metre there is probably there is some other nodules or maybe even the digging because the nodules are quite sensitive to small things then also digging if not careful then probably that would damage the nodules <P:05> but the the the the the soil is is moist is not that very hot because bacteria could be killed by very high temperature by draught <P:05> this is nodules of (alfalfa) , and it's quite common to see nodules of acacia in the (xx) coming out from the poly- (xx) . and agroforestry can produce or can give us quite a number of advantages especially in relation to soil management rehabilitation of the damaged soil building up of nutrients organic matter protection against erosion <P:09> especially the component of the only component of agroforestry where we besides from the first lecture that to qualify as agroforestry system they must be an only component and this only component , acted four different ways four different processes either processes that add to the soil so addition of organic matter from (xx) below ground (xx) or accumulation of dust which is ri- rich in phosphorus and other nutrients or processes that reduce losses that means capturing , because it is a closed system i would say in agroforestry that an agroforestry system can recycle nutrients and so bringing up the nutrients that go below the crop r- root zone up again to the crops this is er reduces the losses from the system or a process that affects soil physical condition of the structure (xx) or (modulation) of the microclimate micro-organism in the soil , if it (xx) through root opening the the soil through the root system decaying of the coarse roots turnover of the roots probably the the soil texture and structure <P:07> also the effect on chemical condition so a- addition of organic matter that is reducing the pH of the soil . or reducing salinity i also have seen that some some trees can take up quite a lot of , the salt from from from the from the soil and there are different advantage of having trees in the system especially those trees of multi-purpose especially those trees are nitrogen fixing especially trees that possess high-quality litter high-quality litter high-quality pruning and that and trees that are not allelopathic are not excreting things that biochemicals or (phenolic) or (xx) compounds that are toxic to the plants <P:06> i will , i think probably end here because time is passing and then we'll have we should ha- should have to listen to someone speaking today and tomorrow we are having three speakers and only h- tomorrow we are having only one hour because we should have to listen to <NAME> for the PhD she did the first in the centre of jörn laxen , so tomorrow during the from ten to 11 and that would be just reserved for three speakers to give their presentation in in one hour maybe 20 minutes each so the next speaker er should be giving her presentation in , h- half an hour maximum , please so we are here to listen , for your talk today if there is any question please feel free still there is time i can be here till so late so if there is anything unclear and you would like to cover one slide maybe tomorrow </S1>

<S6 PREPARING FOR THE PRESENTATION, P:24>

<S1> and next week we'll on the fourth the exam please if you don't want to come to the exam let me know in advance so that we can organise our when are you going to take it next time but i hope that all of us will be present of course </S1>
<S4> have we to register [for the exam] </S4>
<S1> [pardon] </S1>
<S4> have we to register [for the exam] </S4>
<S1> [no need] for registration just try to be here on the course </S1>
<S3> [and the time] </S3>
<S1> [there will be plenty of] space plenty of papers from ten to . i hope you will finish in two hours but regulation says from four t- from ten to two but i hope that er maximum of two hours you will finish your your your answers </S1>
<DISCUSSION USEMD290>
