This is an expansion / revision of LUP Note AAH/8/87

This note is an expansion of what was presented as LUP Note AAH/8/87 in the 1986/87 Annual Report of the Land Use Planning Section of the ADD, WSDC.

In LUP Note AAH/4/87 it was proposed that certain ploughing and fertiliser treatments be attempted to help establish pasture grass in the Livestock Holding Compound at Kilo. The design proposed at that time was considered to be too complex to install and a simpler trial was designed.

The soils in the Livestock holding Compound are Basement Complex and are considered to be nascent non-saline alkali, are compacted with low infiltration rates and are generally devoid of much vegetation. Background data on the general characteristics of Basement Soils can be found in Land Use Planning Notes AAH/02/87 and AAH/04/87. The use of the term nascent non-saline alkali is defined in note AAH/13/86.

When soil depth is not limited by rock or gravel these soils have high fertility potential with cation exchange capacity (CEC) usually in excess of 20 me/100g but they do have low levels of nitrogen, available phosphorus and, probably, potassium.

Water holding capacity (AWC), though not measured, should be high and be in the order of 15 to 20 cm of water per metre of soil. Unfortunately, the compactness of these soils normally prevents infiltration of precipitation and the soil hence never contains as much moisture as it could hold. Much of the precipitation that does fall is lost as run-off.

The Livestock Compound, approximately 6 hectares in size, lies on bare Basement Soils apart from the upslope area where there is a skim of Qoz type sand of variable depth. The compound was previously seeded with pasture grass using the Kim Seeder but the results proved disappointing with grass establishing on the sandy areas but not on the bare, hard areas. The sites of old roads through the compound show even less signs of vegetative growth than the rest of the compound.

Simple laboratory tests carried out by the Land Use Planner (LUP) and the visiting Agricultural Engineer (1987) indicated that these Basement soils did not have particularly stable structures, especially in the topsoil. This indicated that the soils would probably have benefited from inputs of gypsum as a soil structure stabiliser. It was also noted that some of the (upper) subsoils had better structure and this was associated with accumulations of calcium carbonate.

The aims of the trial, which was to be assessed visually only, were to try various tillage treatments, some water-harvesting inputs, addition of low rates of gypsum and inputs of available fertilisers to see if there were any effects on freshly sown grass seed and on transplanted trees.

The various factors tested were:

• Addition of gypsum in attempts to improve soil structural stability
• Inversion of the soil to bring the more stable calcium carbonate rich material to the surface
• Chisel ploughing to about 15 cm depth
• Sub-soiling to between 25 - 40 cm depth.
• Strip cultivation leaving bare areas as water harvesting run-off zones
• Addition of phosphatic and nitrogenous fertilisers
• Fertilisation of previously planted trees
• Planting and fertilising additional trees in holes excavated to 50 cm depth
• Re-seeding the whole compound with grass.

The overall aims of the various treatments being to try and increase moisture penetration, improve soil structure, re-establish a pasture cover and re-instate a nutrient cycle via the trees. The trees, of course, if they grew would also eventually provide shade and browse materials for animals held in the compound.

The areas where specific tillage inputs were done can be seen from Figure 1. In general the tillage (ploughing) was done at right angles to the slope but, as can be seen in Figure 1, all the tillage strips are not quite parallel - mainly due to the inexperience of the operators of the equipment. This does mean that the run-off : run-on ratios for water harvesting are not as exact as perhaps they should be.

The corner of each tillage strip was marked with a concrete marker post for future locational purposes. The eastern and western limits of cultivation were marked by a furrow, set up with a mould-board plough, running N - S and NW - SE respectively, the furrow being located about 10 metres in from the compound fence.

Sub-soiling was done between 30 March and 9 April 1987. The ground was very hard and penetration of the sub-soiler was very variable (25 - 40 cm). On the line of the old roads penetration was virtually nil. As can be seen from Figure 1 the sub-soiling was done as sub-plots (or strips) in Strips 1 and 2 whilst Strips 3 - 9 were totally sub-soiled.

Chisel ploughing was done on 14 June, almost one month after sub- soiling, after the sub-soiled strips had been surveyed and mapped. On the plots receiving chemical inputs the chisel ploughing was done after the inputs were applied (broadcast by hand).

Mould-board ploughing was done on 11 June and penetration varied from about 10 - 30 cm depth depending on the hardness of the ground.

The intention was that Strips 1 and 2 would be cultivation only and moisture accumulation should be from direct rainfall only - it is possible, however, that there could have been some water-harvesting effects on the upslope edges. Water-harvesting could well have occurred in Strips 3 to 9 but the effects of re-seeding using the Kim Seeder may have restricted the run-off effects to some extent. Table 1 shows the approximate run-off : run-on ratios for strips 3 to 9.

 Table 1 Run-off : Run-on Ratios

* Strips not parallel and so ratio varies

 6 CHEMICAL INPUTS

Various rates of gypsum, triple superphosphate (TSP), rock phosphate (RP) and ammonium nitrate, alone and in simple combination, were applied by hand broadcasting in Strips 3 to 9 and incorporated into the soil surface by making a pass with the chisel plough.

The inputs applied can be seen in Table 2.

Notes

: TSP - Triple Super Phosphate

: RP - Rock Phosphate

: N - Ammonium Nitrate

: Gyp - Gypsum

The whole compound, areas cultivated and areas uncultivated, was seeded on 22 - 24 June 1987 with Cenchrus Ciliaris Cultivar Gayndah at the rate of 0.4g per square metre. The seed was applied using the Kim Seeder operating along the contour (parallel with the alignment of the cultivated strips). The equipment used was the Kimseed Chisel Seeder fitted with spring tynes working to a depth of 50 - 100mm.

The grass seed was supplied and applied by the Range and Pasture Section, ADD, WSDC.

During 1985/86 many trees were planted and in the course of 1987 many others were planted. As explained earlier the point of planting trees being to try and re-establish a nutrient cycle, to aid the generation of a pasture, and to offer browse and shade to animals.

The location of all trees is shown in Figure 2 and all chemical (fertiliser) treatments applied to the trees shown in Table 3. Full details of tillage treatments etc are given in the Appendix.

These trees, planted in July / August 1986, are noted as to having been planted in shallow holes, the holes being no more than 15 cm deep. Small basins were constructed around the trees and in June 1987 these basins were enlarged to about 100 cm diameter. The purpose of the basins being for watering during the dry season. Fertilisers were worked into the surface soil of each basin.

There were 157 such trees and the 14 treatments were replicated 11 times covering 154 of the trees. The balance, 3 trees, were given no input, as indicated in the Appendix.

Holes for the trees planted in 1987 were excavated to about 50 cm depth in attempts to improve the root and moisture penetration since it was felt that the roots of the seedlings would have great difficulty penetrating the compact subsoil.

Gypsum treatments were mixed to some depth in the hole before the seedling was planted whilst other inputs were worked into the surface soil of the surrounding basin ( about 100 cm diameter) after the seedling was planted.

At sites with nil inputs the hole was partly refilled with the loosened excavated subsoil before the seedling was planted.

Combinations of gypsum (5t/ha), phosphatic fertilisers (TSP and RP at 30kg/ha and 75kg/ha respectively), nitogenous fertiliser (ammonium nitrate at 180kg/ha) and organic manure (10 t/ha) were applied as indicated in Sections 8.2 and 8.3 and as detailed in Table 3 and the in the Appendix.

The treatments were applied at random and ignored the fact whether other treatments, cultivation plus inputs, occurred at or near the site, but other treatments were noted.

Notes:

TSP Triple Super Phosphate

RP Rock Phosphate

Nitrogen Ammonium nitrate

OM Organic Manure

As was said in the introduction most observations were to be done on a visual basis only. At the end of the wet season the most obvious effects were noted to be growth of vegetation and these observations are presented below.

Local vegetation was more vigorous, taller than in the non-tilled areas but not significantly better.

Overall no large obvious difference over the non-tilled area though where sub-soiling done, and close to the run-off : run-on interface, there was possibly more vigorous growth of local vegetation.

Overall, more, taller local vegetation than in nil-till areas. No obvious differences between the 3 rates of TSP applied. Furrows were still visible in places.

 9.2.4 Strip 4 - Subsoiled and chiselled with RP inputs.

Effects of the treatments less obvious than in strips with TSP, Nitrogen and gypsum. Some Cenchrus grass had established.

No obvious differences between the 3 rates of gypsum but, overall, there was more, taller local vegetation than in the non-tilled areas.

Treatment B (2t/ha gypsum) appears to have given better vegetative growth than treatment A (1t/ha gypsum). Growth also better close to the run-off : run-on interface.

Ploughing was deeper in sub-plot B as the soils in sub-plot A were much more compact and hard.

Treatment B (2t/ha gypsum) appears to have led to more, stronger local vegetation growth. Poor grass germination and growth but many water melons (self-seeded).

There is a water channel passing downslope through the east end of subplot B and hence water supply must have been better. This could be the reason for better growth in subplot B rather than the chemical inputs.

9.2.8 Strip 8 - Subsoiled and chiselled with nitrogen and gypsum inputs.

Local vegetative was growth stronger than in the un-tilled and untreated area though little grass germination. No obvious differences between A (1t/ha gypsum) and B (2t/ha gypsum).

Fairly good growth of local vegetation but none of the seeded grass germinated and grew. The good growth was probably due more to water collection from adjacent ditches but there was some definite effect from the treatments over the nil-tilled areas.

All the tilled strips appeared to show better growth of vegetation than the un-tilled areas, but:

(a) Tilled areas have local vegetation (species not recorded) rather than the sown Cenchrus sp. grass

(b) Tillage without inputs of chemicals (fertilisers) led to less well developed vegetative cover (than with inputs)

(c) Input of rock phosphate (RP) alone apparently gave no beneficial effect over tillage alone

Strips with gypsum inputs all showed better vegetative growth than the non-gypsum treatments and the surface soil appeared to be more friable and cracks did develop during dry spells.

Two treatments (TSP + gypsum and RP + gypsum) appeared to give better responses with the 2t/ha gypsum compared to the 1t/ha gypsum.

Effects of moisture would appear to have been more significant than the tillage treatments and the inputs of the various fertilisers since:

- the lowest lying area at the southern apex of the compound where the cut-off ditches converge had no tillage and no inputs but the vegetative growth was the strongest in the compound.

- there was very good vegetative growth in and around a natural waterway, which runs through part of strip 7B, where there were signs of deposition of water borne fines (silt and clay).

The trial compound was monitored regularly throughout the wet season and the trees planted in 1986 had their height recorded early in the season and again at the end of the season. All recorded data are to be found in file LUP/8/3 and are not reproduced here.

The growth increments achieved during the months of August to late September 1987 are shown in Table 4. The increments by the various species are not detailed in this table.

Notes : * One sample gave abnormally high result and original reading suspect hence data omitted from means.

: ** One tree lost through termite attack.

:*** Refer Table 3

10.3.1 All treatments, apart from number 11 ( nitrogen plus organic manure) gave some extra growth increment compared to the control treatment (number 14).

10.3.2 Prosopis sp. showed, on average, about 10 - 11 % growth increment and Acacia sp. gave greater increments but there were too few Acacia sp. to draw sound conclusions.

10.3.3 Considering all species (apart from Acacia nilotica, where only one tree existed) treatments 5, 1 and 12 gave increments a full 1% greater than treatments 8, 13 and 6 , and these six treatments gave increments above the average for all treatments.

Greatest response seemed to come from treatments 1 and 5, both of which contained gypsum, and the influence of the gypsum in improving soil structure leading to better infiltration of soil moisture may be the explanation.

Nitrogen only seemed effective when applied with phosphate and organic matter and this suggests that a balanced fertiliser may have to be used when nitrogen is being considered.

As these trees were only planted at the start of the wet season there was little point in trying to assess growth increments. What was done was to take note of the number of trees that survived. Full data are to be found in file LUP/8/3.

The following tables summarise the observations made on the numbers of planted trees that survived, which inputs of fertilisers led to the best survival and what influence cultivation had.

Notes:

Nil* - Nil inputs, controls.

/ - None in this group

• better moisture resources in the soil due to improved infiltration brought about by loosening the soil.
• more extensive rooting system developed due to the soil being loosened and the roots able to forage for moisture and nutrients.
• perhaps the labour force did not dig the planting holes to the depth specified and hence the roots were unable to penetrate the sub-soil where cultivation was not done.

Inversion alone gave 100% survival of plantings, chisel ploughing plus sub-soiling gave 75% survivors and other tillages gave 67% as compared to 49% survivors in nil-tilled areas.

In nil-tilled areas best survival rates were achieved with TSP + N, Gypsum and TSP + N + OM in decreasing order.

Input of TSP + N gave the best survival rate and treatments with nitrogen generally gave improved survival rates, as did most treatments including gypsum.

Rock phosphate (RP) alone produced no survivors and most treatments including RP gave reduced survival rate (apart from RP + N).

Seven species of trees were planted but only Acacia albida had sufficient replicates to warrant study of survival rates of the various species. Treatments 9, 7 and 5 (RP + N, TSP + N and gypsum + OM respectively) appear to give better survival rates than the norm, but tillage operations seem to be much more important for the survival of new plantings.

Overall it can be concluded that unless the root zone for tree seedlings is improved, made less compact and hard, the survival rate that can be expected is low, about 50%. The major beneficial effects of tillage must be in breaking the hard, capped nature of the soil and allowing rainfall to penetrate the profile and be available to the plant. Loosening the soil would also allow the roots to forage for moisture and nutrients.

From the figure it can be seen that the accumulated rainfall was just less than 260mm and of that 159mm (61%) fell as relatively massive events. Of the massive events, 4 were in excess of 20mm / day with a total accumulated precipitation of 102mm (40% of the grand total). From observations made at Kilo early in the season it is apparent that these soils lose a great deal of precipitation as run-off but no estimate has been made of the percentage lost.

 12.2 Grass Seeding and germination.

The grass seed sown, Cenchrus ciliaris sp. showed very poor to nil germination and survival. It has been concluded that this was largely due to the seed being sown during periods when there was little or no moisture available in the surface soil.

In June the seed was sown during what must have been a negative moisture balance period - there were 11mm of precipitation on June 22 - 23 and there was no more rain until the 26^th June (2.5mm). Even with a low daily evaporation rate the surface soil would have been dry throughout much of this period.

In July the next seeding was done at the start of a 17 day relatively dry period and the third sowing, done in August, did not coincide with a prolonged period of rainfall. It is concluded that the grass seed was either taken by ants and termites before there was sufficient rainfall to allow germination or that there was just never enough moisture in the surface soil to allow germination and growth.

With the present rainfall, distribution and assumption that there are large losses of precipitation through run-off and evaporation there seems little likelihood of being able to re-establish grass cover on the Basement Soils, certainly not using the species of grass used in this trial.

Perhaps with more judicious timing of sowing the seed it might prove possible to re-establish cover but it would be difficult to know exactly when to sow. Perhaps a full study of recent rainfall records and patterns might assist in this aspect.

The tillage treatments and water harvesting done to date have not helped the sown grass establish, but they (the treatments) have helped local varieties of vegetation to flush. The question must be asked if the grass species used was suitable to the environment and was the sample of seed good?

 13 CONCLUSIONS

This simple trial did not seem to achieve very much, and obvious effects are not too noticeable on the ground. However, it can be said that:

Tillage treatments did help newly planted trees to survive, presumably by loosening the hard, compact soil and allowing rainfall to infiltrate and so increase moisture reserves in soil. Similarly, loosening the soil probably allowed the roots to forage more widely for moisture and nutrients.

Of the various tillage treatments, survival rates of newly planted trees were most improved by inversion followed by chisel ploughing plus sub-soiling. It is not surprising that inversion proved best since in the Hashaba Tillage Trial - LUP Note AAH/10/87 - inversion of Basement Soil led to better penetration of rainfall from the depth of penetration and moisture content standpoints. There may well also have been some alteration to the soil pH and the structural stability through inversion (AAH/10/87) which would have proved beneficial to the establishment of the trees.

The tillage treatments, with or without inputs of chemical fertilisers, did not lead to the establishment of cover of Cenchrus sp. of grass. From a study of sowing dates and the rainfall records it is concluded that the reason for the non-germination of the grass was lack of soil moisture at the critical times of sowing. However, there is the possibility that the grass species used was unsuitable or that the seed was not good.

The tillage treatments did, however, encourage flushes of local vegetation and it will remain to be seen if there is continuation of this improvement in natural vegetation during the 1988 wet season. It is possible that the rooting systems of the existing vegetation will help establish some soil structure and form pores for the ingress of rainfall.

Various inputs of gypsum and fertilisers failed to show any obvious advantages over tillage as far as the regeneration of the natural vegetation was concerned, though there were some apparent improvements. However, some of the various inputs did improve the incremental growth of existing trees and some inputs increased the survival rates of newly planted trees.

From the observations made it seems apparent that the factor most likely to aid regeneration of vegetation on such soils is soil moisture. Any further studies should concentrate on ways of improving the amount of rainfall that can be infiltrated by the Basement Soils. This topic is more fully covered in LUP Note AAH/10/87.

A.A.Hutcheon

24 May 1988

Notes Refer Table A2

Species names and seedlings supplied by Kilo nursery.