Salgado, M.L.M.

Coconut Research Institute Repository

SOIL MANAGEMENT ON COCONUT ESTATES By M . L . M . S A L G A D O , Soil Chemist, Coconut Research Institute. SO I L m a n a g e m e n t aims at main ta in ing the soil in such a condi t ion that m a x i m u m use wil l b e m a d e of inheren t and added fertility and of soil mois tu re for t he benefit of the c r o p . Correc t m a n a g e m e n t of the soil is as i m p o r t a n t as correct m a n u r i n g for c r o p p roduc t i on . I t s p r imary object ive is t o mainta in the soil in an o p t i m u m physical cond i t ion as a m e d i u m for plant g r o w t h and for t he conserva t ion of the soil and its fertility. Besides soil mois tu re in which the nu t r ien ts en ter i n t o solut ion and are abso rbed by the p lan t , the soil needs an adequa te supply of air r o u n d the roo t s in o rde r t o mainta in an o p t i m u m con ten t of oxygen . T h e soil shou ld therefore be kept permeable so tha t wate r can dra in t h r o u g h a t a reasonable rate. T o some extent these factors are cont ro l led by p r o p e r cul t ivat ions which are dis­cussed in the course of this paper . Some cul t ivat ion practices o n coconu t estates are based o n s o u n d scientific pr inciples , o thers on t radi t ion , a n d yet o thers on misconcept ions a n d fallacies. Unfor tuna te ly we have l i t t le ex­per imenta l data that have critically examined some of the t radi t ional practices a n d as such there is b o u n d to be some cont roversy . -E v e r y i t em of cul t iva t ion costs m o n e y and adds to the cost of p r o d u c t i o n of coconu t s and it is therefore essential tha t r e d u n d a n t a n d superfluous cul t ivat ion process shou ld be discarded and essential cul t ivat ion restr icted to the m i n i m u m . Ploughing I n the case of annua l c rops such as cereals, p l o u g h i n g is the first tillage opera t ion in the p re ­pa ra t ion of a seed bed . I n the case of a widely spaced perennia l c r o p such as coconu t s , p l o u g h i n g is d o n e for qui te a different pu rpose and the benefits tha t could b e expected to result f rom p l o u g h ­i n g may be briefly considered. A n u n p l o u g h e d soil is compac t and rainfall t ends to run off the surface instead of percola t ing in to the soil. P l o u g h i n g -makes the soil p o r o u s a n d absorp t ive . Similarly the aerat ion of the soil is i m p r o v e d . O r g a n i c ma t t e r in the form of grass a n d weeds is tu rned in to the soil and these o n decompos i t ion release nu t r ien ts wh ich are absorbed by the pa lm. T h e fo l lowing po in t s shou ld b e no t e d w h e n p l o u g h i n g c o c o n u t lands :— Time of Ploughing.—Ploughing shou ld b e d o n e d u r i n g the rainy seasons, preferably at the beg inn ing of the m o n s o o n . Slope.—Ploughing shou ld always b e d o n e a long the c o n t o u r and never d o w n the s lope. P lough- fu r rows d o w n the s lope cause eros ion and can result in gul lying. Cross -p lough ing as d o n e in the old days in t w o direct ions can be definitely harmful . 153 A S E R R A T E D D I S C - H A R R O W . Depth.—Deep ploughing should be avoided and depth of ploughing should not exceed six inches. This should be particularly kept in mind where tractor ploughing is done. There is an extensive body of experience that has shown that deep ploughing can cause a set-back to the palms. Frequency.—-It is usual to plough coconut lands once in two years. In the case of lands that have not been cultivated for long periods, annual ploughing of alternate rows, rather than plough­ing the entire area once in two years is to be recommended. In any case, in areas subject to drought conditions, annual ploughing of alternate rows is to be preferred. Should a drought follow plough­ing there would be less risk of the palms suffering a set back if the root system of only half the area is disturbed by ploughing. Under tropical conditions too frequent ploughing can be harmful as high temperatures would favour the oxidation of organic matter. Ploughing the same row once in two years can be con­sidered a satisfactory compromise. Soil T u r n i n g . When labour was plentiful and cheap the traditional method of cultivation on coconut estates was soil turning with the mammoty or hand-hoe. It is an ideal method of turning the soil and bury­ing organic matter. The clods are aligned in such a way that rain water effectively percolates into the sub-soil. Even today it is the only method of cultivating water-logged lands, provided with deep drains in proxi­mity where ploughs cannot be used. This method is very effective in breaking the mat of roots, hissa on such'soils. H a r r o w i n g Disc-harrowing is an established routine practice on coconut estates and is carried out during the dry season in the expectation that a surface dust mulch conserves soil moisture. Experiments have, how­ever, shown that a dust mulch can­not appreciably reduce the rate of evaporation of water from the soil. It is an obsolete idea that disc­harrowing conserves soil moisture because it breaks the capillary tubes that bring moisture up from the sub-soil. There is no such upward movement of water unless there is a water table within a few feet of the surface. The benefit of disc-harrowing Mechanised farming makes it possible to illuk under control. keep cover crops and 1 5 4 is probably due to the killing of weeds which by transpiration can cause a loss of soil moisture during dry weather and also compete for plant food with the palms. It is an effective and economical method of controlling weeds. The dead weeds are left in situ on the surface as a dry vegetable mulch which further helps to shade the soil and thereby conserve moisture. Where manure is applied by broadcasting and ploughing, disc-harrowing is a useful operation to break the clods and effectively cover the manure. Otherwise if heavy rain fol lows there is the possibility of mechanical loss of manure removed by run off with the tine soil particles. M u l c h i n g There is a considerable amount of experimental data on orchard crops in other countries (including tropical countries) which show that the practice of applying a layer of dead vegetable waste material on to the surface of the soil surrounding the tree is effective in conserving soil mois­ture. The surface layers of the soil are kept cooler and at a more even temperature and damper and more permeable to water than an unmulched soil. Thus working with coffee in Tanganyika it has been shown that the temperature of the soil at two inches depth might vary by 120 C during the day, whilst under a mulch it varied by i° or 3 0 C. The mulch slows d o w n the rate of evapora­tion from a bare wet soil very considerably and would therefore be particularly useful in areas subject to drought. O n a coconut estate the materials that can be used for mulching are husks and fronds and where estates are in proximity to fibre mills, coir dust. / \uskMulcb.—Husks can be used as a mulch round palms by closely packing one layer, one against the other, with the convex side facing upwards. In the case of young palms it may extend up to a distance of 4 to 6 ft. from the base of the palms depending upon the age of the palms. It is particularly effective in preventing weed growth round the palms, and especially in the early stages of planting helps to mitigate the adverse effects of droughts by conserving soil mois­ture round the palms. Bearing palms can be similarly mulched up to a distance of 6 feet from the base. Here too it is very effective in preventing the lux­urious weed growth that appears round the palms after manuring and competes with the palms for plant food and moisture. HUSK BROADCASTING. The husks are laid in strips. 155 Besides moisture conserved, 'he potash in the husks leached d o w n by rain into the soil benefit the palms. Where husks are available in plenty and cannot be otherwise utilised due to exigencies of labour, rather than accumulating in heaps, it may be broadcast in the squares as a very useful mulch. O n gravelly soils this method of mulching gives g o o d results. Husks broadcasted in this manner-decay soon and could be ploughed into the soil after two years. Fronds.—Fronds, without the butt ends, cut into short lengths can be useful for mulching round palms as with husks. It is not advisable to use these for mulching seedlings in the early stages, as these tend to attract white ants, which can d o considerable damage. B u r n i n g of D e b r i s FIRE ! A n undesirable traditional prac­tice, which appears to die hard, and is typical of bad soil manage­ment is the burning of debris, particularly heaps of fronds, on coconut estates in the form of systematic night fires. Such materials should be used as mulches or if mulching makes a demand on labour, allowed to decay in situ. The only materials that need be burnt are butt-ends and stumps, particularly the latter which breeds coconut black beetle. D r a i n s a n d D r a i n i n g The proper control of the water required in the soil is one of the most important aspects of soil management. Excess ground water can do as much harm as I , . . slack of water. D e s t r u c t i o n o f v a l u a b l e o r g a n i c m a t t e r o n a c o c o n u t e s t a t e . Drains and Water Conservation.— The subject of soil and water conservation will not: be considered here except to state that a system of contour drains, forms the first line of defence for this purpose. Draining Water-logged Lands.—By drainage we understand the removal of the superfluous or free water from the uppe - layers of the soil and thus a lowering of the water table. Coconut lands which come under this category are of two types : 1 5 6 U n d e r the first ca tegory w e h a v e t o consider those lands tha t remain wa te r - logged t h r o u g h a g rea te r pa r t of t he year because of t he impermeab le na tu re of t he heavy clay soils a n d lack of out le ts t o d ra in off excess wate r o w i n g to the low- ly ing s i tuat ion of the land. I n this case, deep drains at least 3 ft. w ide and 3 to 4 ft. deep shou ld b e cu t t o l o w e r the water table . H u s k s can b e used w i t h advan tage o n such lands t o raise the g r o u n d level r o u n d the pa lms a n d thereby l o w e r the water- table a n d increase the effective r ange for r o o t deve lopmen t . T h i s can b e d o n e by plac ing a layer of husks , w i t h the convex side facing u p w a r d s a n d cove r ing w i t h the soil r e m o v e d f rom the dra ins . N o r m a l l y dra ins a re cu t be tween al ternate r o w s of pa lms and in ex t reme cases of pe rmanen t wa te r - logg ing drains are cu t be tween every r o w . I t is unfor tuna te ly a c o m m o n s ight t o find such drains filled w i t h h u s k s , coi r dus t o r f ronds . As the object of the d ra ins is t o r e m o v e excess wa te r and lower t he water- table , refilling w i t h husks o r coir dus t will only defeat t he p u r p o s e of d ra in ing . I n t he o the r ca tegory of l ands , t he soil cond i t ions are different a n d consists of a t o p soil which is sandy, usual ly c i n n a m o n sand of va ry ing dep th , over ly ing an impermeab le clay sub-soil . D u r i n g d r y wea the r there is n o appa ren t wa te r - logg ing , b u t d u r i n g the rainy season the wate r table r ises close t o t he surface. O n such soils, therefore, the p r o b l e m is lack of soil mo i s tu re d u r i n g the d r y season a n d excess wa te r caus ing wa te r l o g g i n g d u r i n g the ra iny season. H e r e t oo deep drains are necessary a n d whe reve r possible shou ld lead in to roads ide dra ins , wa te r courses o r o the r out le ts t o lead off the excess g r o u n d waters . A t the same t ime the texture of the t o p soil shou ld be i m p r o v e d by b u r y i n g husks to conserve moi s tu re d u r i n g d r o u g h t s . O n such sandy soils m a n u r i n g is essential t o p r o d u c e g o o d c rops , b u t the pa lms wil l fail to r e spond unless dra ined . Claying . O n l ight sands , such as the mar ine sands , w h i c h h a v e in their immedia te n e i g h b o u r h o o d beds of clay, such as l a g o o n clay (part icularly near t he M a d a m p e a n d Chi law lagoons) a t tempts h a v e been m a d e to i m p r o v e the tex ture a n d fertility by inco rpo ra t ing the clay o n the sands . Claying was an o ld E n g l i s h pract ice , accord ing to w h i c h 50 t o 150 car t loads used to b e appl ied p e r acre a n d s u b s e q u e n d y p l o u g h e d in. U n d e r the cond i t ions of c o c o n u t estates referred t o , even w i t h a m o d e r a t e ra te of appl icat ion the economics of claying is h igh ly doubt fu l . T h e reverse process o f app ly ing r iver sand t o heavy clay soils has been sugges ted a n d even h e t e t he economics of a t t emp t ing to i m p r o v e such unfavourable soils is quest ionable . O n e has t o face t he fact tha t soils of this na tu re shou ld neve r h a v e been p l a n t e d w i t h coconuts . Weeding Clean w e e d i n g of c o c o n u t estates was advoca ted in the o ld days a n d even as late as 1923, the . s ta tement was m a d e in Fe rguson ' s C o c o n u t Planter ' s Manua l tha t " it wi l l n o t b e l o n g before an estate w i t h grass g r o w i n g a m o n g s t the palms will b e a rare s i g h t . " 157 Since then t he d a n g e r of clean w e e d i n g has been apprecia ted, a n d except for weed ing r o u n d seedlings a n d y o u n g pa lms , m o s t estates h a v e a cover of grass grazed b y catt le. Selective weed ing of certain w o o d y a n d herbaceous plants w h i c h can seriously compe te w i t h the ' pa lms shou ld be carr ied ou t , in t he earliest s tages. T h i s shou ld be d o n e whereve r poss ible before t he weeds flower a n d set seed. O f these Hyptis suaveolens has rapidly spread in c o c o n u t estates. T h i s is a qu ick g r o w i n g weed w h i c h if n o t con t ro l led in t he early stages m a y g r o w to a he igh t of t w o feet. I n the early stages o f g r o w t h i t can b e con t ro l led by h a r r o w i n g , b u t if a l lowed to b e c o m e w o o d y h a n d weed ing is inevi table . A he rbaceous w e e d wh ich is rapidly spread ing o n c o c o n u t estates is Euphorbia geniculata. Cenchrus echinatus, w i t h i ts spiny seeds , is an undes i rab le grass w h i c h once establ ished is diffi­cul t t o eradicate. Similarly the G i a n t m imosa , Mimosa invisa w i t h i ts l a r g e spines a n d even the c o m m o n sensit ive p lant , Mimosa pudica, t h o u g h as legumes are beneficial p lants to the soil, s h o u l d n o t b e a l lowed to spread u n d e r coconu t s as they interfere wi th l abourers w h o have to w o r k ba re ­footed. Tephrosia purpurea (Sinh. Pila) a n d Crotolaria species (Sinh. Andanahi r iya) are useful l egumes w h i c h shou ld b e encou raged and shou ld n o t b e h a n d weeded , b u t al lowed to g o to seed and then h a r r o w e d o r p l o u g h e d so tha t a second c r o p cou ld regenera te f rom shed seeds. SEEDS ! FOR YOUR REQUIREMENTS OF GUARANTEED SEEDS OF ALL Tropical Agricultural Crops , C o v e r Crops, Green Manure Crops , forest , Shade, Fence, Fuel, Timber, Ornamental & Hedge Trees, Grasses, Food Crops , e tc . Also Insecticides,-Snail, Slug & Rat Poisons, Baskets, Lime, etc. CEYLON PRODUCE AGENCY S E E D S M E N — E X P O R T E R S — I M P O R T E R S . M A T A L E C E Y L O N . 158 

Soil management on coconut estates

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Soil management on coconut estates

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Coconut Research Institute Repository