A field experiment using 15N was carried out at the Indian Agricultural Research Institute, New Delhi during the crop year 1985–1986 to investigate the possible economy in fertilizer nitrogen applied to rice and succeeding wheat by growing a summer leguminous green manure (Sesbania aculeata) and incorporating it in soil before transplanting rice. Grain and straw yields of rice with 60 kg N/ha after green manuring were slightly greater than with 120 kg N/ha after summer fallow. Thus summer green manuring can lead to an economy of 60 kg N/ha in rice. 15N analysis showed that green manuring contributed 4·7–5·6% N of the total taken up by rice and 1·9–4·8% of that taken up by the succeeding wheat, depending upon the rate of fertilizer N applied to rice.

15N analysis showed that at 60 kg N/ha applied to rice, 35·4% was recovered by rice, 41% by the succeeding wheat and 16·7% was left in the 0–45 cm soil layer after summer fallow; after green manuring 32·8% N was recovered by rice, 3·0% by succeeding wheat and 22·6% was left in the soil. Thus 56·2 and 58·4% of applied N could be accounted for after summer fallow and green manuring, respectively. At 120 kg N/ha about 60–61% of applied N could be accounted for. Thus about 40–44% of N applied to rice was lost by the various loss mechanisms operating in rice fields.

The effects of applications of sodium chloride (NaCl) and potassium chloride (KCl) ranging from 0 to 720 kg Cl/ha on the yield and uptakes of chloride (Cl) potassium (K) and sodium (Na) by fodder beet were studied in field experiments at two sites in New Zealand. At 360 kg Cl/ha applied, both NaCl (590 kg/ha) and KC1 (758 kg/ha) increased significantly yields of fresh roots, dry roots and fresh sugar content of fodder beet over the minus-Cl plants. Compared with the sulphate anion, chloride application stimulated K uptake in tops and roots. Results indicated that in the beet crop, uptake of K is enhanced with the presence or addition of Cl (as NaCl) compared with SO4 (as NaSO4).

In both soils, total (tops and roots) uptakes of K, Cl, and Na were significantly correlated with fresh roots, dry roots and fresh sugar content. Multiple regression analyses showed that total K uptake was the main nutritional factor which determined yields of fresh and dry roots in the Templeton soil, whilst in the Wakanui soil total Cl uptake and total K+total Cl uptakes determined fresh root and dry root yields, respectively. In both soils, high Cl uptake was required for increased sugar yields.

Voluntary intake and apparent digestibility of tree willow (Salix matsudana Χ alba) and of osier willow (Salix viminalis) were measured with male sheep and goats and voluntary intake only with male deer. Both willow species had been selected for extremely rapid growth, and were grown in coppices on high fertility soil. In a first experiment spring primary growth of both willows was fed to sheep, goats and deer in early summer, whilst in a second experiment summer regrowth (i.e. secondary growth) of osier willow was fed to sheep and goats in autumn.

Although the ratio of readily fermentable to structural carbohydrate (0·51–0·70) and total N concentration (18–24 g/kg D.M.) in primary growth of the willows was less than normally found in high quality fresh temperate forages, the values were similar to those of many dried forages normally used as supplements. Averaged over sheep and goats, voluntary intake of digestible D.M. was 22% less for osier than for tree willow, this being associated with higher concentrations of lignin (197 ν 182 g/kg D.M.) and of condensed tannin (66 ν 29 g/kg D.M.) in the osier willow. The lower digestible dry-matter intake was attributable to both lower voluntary intakes and lower digestibility of the D.M. (0·57 ν 0·64). Both voluntary intake and apparent digestibility of secondary growth willow were lower than that of primary growth.

When expressed as functions of the amount required for maintenance, voluntary metabolizable energy intake of goats was approximately double that of sheep, both for primary growth (2·2 ν 1·1) and for secondary growth (1·8 ν. 0·7) willow. This was attributable to consistently higher voluntary D.M. intakes/kg W0'6 by goats, and to a trend for higher digestibility than sheep, which attained significance in Expt 2but not in Expt 1. The ratios of dry-matter intake/kg W075 per day for sheep: deer: goats fed primary growth willow were 1·0:1·5:1·9, with deer thus being intermediate between the other two species. There were no differences in voluntary intake (g/kg W0·75 per day) of sheep, goats and deer fed a high quality lucerne hay.

It was concluded that willows grown during spring and summer could adequately be used as supplementary feed during summer droughts and that willow could be used most effectively if fed to goats, followed by deer, with sheep being the least efficient. Tree willow is a preferred choice to the osier willow used here, and it was further concluded that like Lotus pedunculatus, high concentrations of lignin and condensed tannin, both of which are produced by the same biochemical pathway, are likely to be limiting nutritive value of the more leafy osier willow.

This paper describes an investigation into yield variability and spatial correlations in 129 spring barley trials using small plots between 2·4 and 6·0 m2 in area. We report on the efficiencies of the generalized lattice designs used, and discuss the effects of plot size and year-to-year variations. Results indicate that the recommendations of Patterson & Hunter (1983) on choice of block size apply equally well to small-plot trials. The observed variability and correlations are then discussed and so is the potential for improvement by using alternative designs. Patterns of variability were not at all consistent from year to year, or even between trials in the same year, but it appears important to take account of column effects as well as row effects.

Growth and visceral organ weights of male guinea fowl (Numida meleagris) given different levels of oxytetracycline have been studied in two experiments. In the first experiment 0, 5·0, 10·0, 15·0 and 20·0 mg oxytetracycline per kg diet were given to male guinea fowl from day 1 to 12 weeks. Body weight showed significant (P < 0·05) increases with incremental levels of the antibiotic up to 10 mg/kg diet. No further increases in growth were recorded with supplementation above this level. There were no treatment effects on the gizzard, lungs and male reproductive organs. Only the heart, liver and intestine weights were significantly (P < 0·05) affected by the treatment, and then only at the highest (20 mg/kg) of the inclusion rates examined. A second experiment was conducted to find out if the growth response obtained with 10 mg/kg oxytetracycline could be produced with a smaller dose. This was achieved at 6·6 mg/kg.

An experiment was conducted to examine the effect of fertilizer (triple superphosphate) and stocking rate on animal and pasture productivity on Sumba Island, Eastern Indonesia. The Ongole heifers used in the 1-year experiment gained weight during the wet season and lost weight during the dry season at stocking rates of 0·5 and 1·0 head/ha when grazing native Themeda pasture. The dryseason weight loss was arrested when a prepared seed-bed pasture, which contained 21 % Siratro at the start of the experiment was grazed at a stocking rate of 1·5 head/ha. Increasing the stocking rate to 2·5 head/ha on this pasture resulted in an increase, in the weed component of the pasture from 12 to 84% in 1 year.

The mineral content of plucked samples of pasture indicated that levels of Ca and Mg were generally adequate for growing beef cattle and that Na supplementation would be beneficial. Plant N concentration was below 1·5% in the Themeda and Imperatacomponent but above this in the legume at the prepared seed-bed site. The P concentration in the Themeda and Imperata was always below the 0·24 % level required by cattle, as it was in the legume at the end of the experiment.

The introduction of herbaceous legumes into pastures under set stocking conditions can lead to pasture instability.

Twenty fine-wool, ruminally cannulated lambs (average weight 45–9 kg) were used in a completely random design to evaluate the ability of three internal markers to predict dry matter digestibility and two external markers to estimate faecal output. Lambs were allotted randomly to one of four diets: 100% prairie hay (PH), 100% lucerne hay (LH), 50% prairie hay:50% sorghum grain (PS) and 50% lucerne hay: 50% sorghum grain (LS). The trial consisted of a 14-day adaptation period followed by a 7-day total faecal collection period. Feed and faecal samples were subjected to 96 h ruminal fluid and 48 h acid-pepsin digestions, followed by extraction with acid detergent (IVADF) or neutral detergent (IVNDF) solution. Dry matter digestibility (DMD) calculated from feed:faeces ratios of IVADF, IVNDF and acid detergent lignin (ADL) was compared with in vivoapparent digestibility. Ytterbium-labelled forage (YLF) and dysprosium-labelled faeces (DLF) were pulse-dosed via ruminal cannulae, and faecal Yb and Dy excretion curves were fitted to a one-compartment, agedependent model for estimation of faecal output, paniculate passage rate (PPR) and mean gastrointestinal retention time. In vivoDMD in lambs fed PH was greater (P <005) than DMD calculated from IVNDF, IVADF and ADL. In lambs fed LH and LS, in vivoDMD did not differ (P >005) from marker estimates. In vivoDMD for lambs fed PS did not differ from IVNDF or IVADF estimates but was greater than (P <005) the ADL estimate. No differences (P> 005) were observed in recovery among the three internal markers for any of the diets. Faecal output for lambs fed PH did not differ {P >005) from marker estimates but was overestimated by 15 to 20% by YLF and DLF. Faecal output for lambs fed LH was similar to the estimate from YLF, but less than (P <0–05) the estimate with DLF. For lambs fed PS, faecal output did not differ from marker estimates, but YLF and DLF values were 16% lower and 17% higher, respectively. No significant differences were observed in actual and estimated faecal output for lambs fed the LS diet. Estimates of PPR with DLF were numerically greater than YLF estimates for all diets except LS. Correspondingly, mean gastrointestinal retention time was less (P <005) for DLF compared with YLF for all diets except LS.

Experiments were conducted in 1986 and 1987 to determine the influences of plant raising temperature, transplant age, N top-dressing and irrigation regime on the curd initiation and maturity characteristics of the cauliflower variety White Fox. The prime objective of this work was to determine whether changes in crop production practice had an influence on the period between curd initiation and maturity, in order to aid the development of techniques predicting when curds will reach a specific size.

The duration of the period from curd initiation to curd maturity was not significantly affected by any treatment in either year and treatment effects on curd size at maturity were of no practical importance provided that the recommended level of N top-dressing was achieved. It is therefore concluded that changes in production practices within the normal commercial range are unlikely to have any significant practical effect on the use of techniques to predict the timing of crop maturity.

There were large differences between the experiments in the mean number of leaves formed at curd initiation, which ranged from 22·0 to 36·7. In order to interpret these data a relative vernalization stimulus was calculated from 12 leaves onwards. It had a maximum rate of vernalization between 5 and 17 °C and a reduced rate at lower and higher temperatures and adequately accounted for the differences in the number of leaves at curd initiation.

The response of 4 crops of autumn- and spring-sown field beans cv. Maris Bead to irrigation applied during the vegetative, flowering and pod-filling phases was examined during 1981–2 and 1982–3. The crops, grown on a Templeton silt-loam, were irrigated weekly in amounts equal to the difference between the estimated evapotranspiration and rainfall of the previous week using trickle irrigation.

Seed yield of fully irrigated autumn- and spring-sown crops (averaged over the two seasons), was 5·2 and 3·3 t/ha respectively, about 45% greater than the yield of unirrigated crops. The increase in yield due to irrigation was mainly associated with an increase in total dry matter (TDM) production as harvest index varied little within each sowing. The yield response to each mm of applied irrigation water ranged from 0 to 9 kg/ha and did not appear to be related in any way to the developmental phase of the crop when irrigation was applied.

Seed yield within each sowing was closely correlated with the number of beans per unit area and the number of pods per plant. Autumn sowings yielded about 55% more than spring sowings mainly due to a higher harvest index which was associated with a much heavier mean weight per bean.

Seventeen tree species (16 legumes and Eucalyptus saligna) were grown for 4 years on an Ultisol of pH 4·5 at Nakau, South Sumatra, Indonesia. Leaf and wood yields were recorded seven times during the 4-year period and mineral and plant quality measurements were made on leaf samples from the first harvest taken 2 years after transplanting. At this time, leaf and wood yields were highest from Acacia mangium but the yield of this species declined over time. Highest leaf production was recorded for Cassia siamea over the 4-year period.

Mineral analyses of leaf indicated N, K, Ca and Mg to be adequate for animal production in all species. P was below the critical level for animals in all species and Na levels were adequate only in Acacia mangium and Acacia auriculiformis.

Plant quality measures (ADF, NDF, lignin) suggest marked differences could be expected in potential feed value between species through differences in voluntary intake and digestibility.

Water requirements and metabolism were studied in eight each of Barki and Rahmani sheep and eight Baladi goats. The animals were individually housed in the shade in semi-open pens that were located in a non-desert area. The experiments were carried out during spring, summer and winter seasons, and each experiment lasted for 3 weeks during each season. After a preliminary period of 1 week, an 8-day period was then followed during which body weight, daily feed intake and daily drinking water were recorded. Rectal temperature and respiration rate were also recorded in the early morning and late afternoon. Four animals from each group were then weighed and injected intravenously with tritiated water, TOH (001 mCi/kg body weight) and blood samples were collected during a 4-day period to estimate total body water (TBW) and water turnover rate (WTR).

In all seasons studied, the Rahmani sheep had higher TOH disappearance rate (^-values) and WTR and consequently shorter biological half-time (1½) than the Barki. Moreover, the Barki sheep showed less thermal discomfort than the Rahmani particularly during the summer. Although the Rahmani sheep ingested more water than the Barki sheep during the summer, the Rahmani sheep had a lower percentage of TBW and their calculated water loss revealed that they were in negative water balance during this season. Accordingly, the Barki sheep seem to perform better than the Rahmani in newlyreclaimed desert areas. Baladi goats appear to be more adapted to unfavourable environmental conditions than sheep. This is based upon the findings that they had lower k-values, lower WTR, longer tiand higher TBW, than the two breeds of sheep.

The growth and yield of four crops of field bean cv. Maris Bead in response to irrigation and sowing date were analysed in relation to leaf area expansion and senescence and their absorption and utilization of photosynthetically active radiation (PAR). Total dry matter (D.M.) production and seed yield were strongly correlated with total green area duration (GAD) and post-flowering GAD respectively.

Total D.M. production was also strongly related to radiation absorbed by the green surfaces of the crop although autumn sowing and drought both decreased the constant of proportionality, i.e. the growth efficiency (Eg). Autumn sowings yielded more than spring sowings because they grew for longer and received 22% more radiation. Their harvest index was also about 40% higher than in spring sowings. These more than compensated for their smaller Eg. Drought decreased yield mainly by decreasing radiation received and Eg. Growth duration was shorter and harvest index was smaller.

The rate of phenological development was strongly dependent upon temperature and to a lesser extent on photoperiod. The average thermal duration from emergence to flowering was 790 °Cd above a base of 0 °C. The time from sowing to the end of the pod growth was well represented by a simple multiplicative model in which development rate was a linear function of temperature above a base of 0 °C and photoperiod above a base of 6 h. The average photothermal duration required for 10 crops was 980 °Cd.

An attempt was also made to determine the crop physiological and environmental factors which govern the change in size of the yield components of field bean crops caused by irrigation and sowing date. The final number of pods per plant was closely correlated with the rate of supply of assimilates during pod filling. Irrigation increased assimilate flux by increasing leaf area, growth rate and total dry matter during pod growth. Both the rate and duration of pod growth were little affected by irrigation. Autumn sowings produced heavier pods and beans due to both a faster rate and a longer duration of growth which were associated with a greater production of assimilate during the seed growth period. Seed growth depends on both the current assimilate and stored reserves, the latter especially when plants were subjected to environmental stress.

Laboratory silos were prepared from lucerne (Medicago sativa)which had been treated with a number of chemical and biological additives. The additives used were the acid additive, formic acid, the sterilant, formaldehyde, the oxidative enzyme, glucose oxidase, and the starch hydrolysing enzyme complex, Termamyl. Silos were prepared in duplicate and pairs of each treatment were opened at 0, 2, 9, 20 and 60 days ensilage. The pH, volatile fatty acid patterns and dry-matter yields were determined and the composition of the residual fibre was determined for cellulose, hemicelluloses, lignin and phenolic acids. The only treatment to enhance the rate of fall in pH was formic acid. The rate of decline in pH of the silages treated with glucose oxidase was not significantly different from the other treatments. The starch degrading enzyme complex did enhance the loss of starch from the lucerne but it did not appear to have any significant effect on the silage characteristics measured. No loss of true lignin was observed from the fibre but most of the phenolic acids present were removed. All the treatments appeared to have a significant effect on the cellulose content which was in contrast to earlier work on ryegrass silages where no effect was observed. On the other hand, the treatments had less effect on the hemicellulose fraction than was observed in the previous work with ryegrass. These results can be explained by differences in the structures of the fibres from lucerne and ryegrass.

In weeks 1–6 of lactation, 11 goats were fed diets adequate in phosphorus content, supplying a basal intake of 2·8 g P/day plus 1·4 g P/kg milk produced. In group 1 (three goats), this scheme was continued until week 16. In group 2 (four goats), P supply was changed from an adequate one to a reduced amount by restricting the variable intake to 1·0 g P/kg milk during weeks 7–16 and the basal intake to 0·8 g P/day during weeks 12–16. In group 3 (four goats), P deficiency was caused during weeks 7–11 by a basal intake of 0·8 g P/day plus only 0·4 g P/kg milk. During weeks 12–16 these goats received the same supply of P provided in weeks 1–6.

Milk yield was depressed in group 3, but not in group 2. Composition of milk was not affected by P intake in either group. Digestibility of organic matter was reduced from 0·73 to 0·64 by P deficiency treatment. Reduction of faecal P excretion in group 2 appeared to enable P homoeostasis even at the reduced level of P intake. The amounts of P and Ca secreted in milk during P deficiency in group 3 clearly exceeded the corresponding net absorptions. During this period, daily faecal P excretion was reduced to 17 mg/kg live weight. P concentrations in blood plasma, saliva and particle-free rumen fluid were also drastically reduced. Faecal excretion of P increased after the animals returned to the diet supplying adequate P. The increase occurred before the pre-depletion P status had been restored.

The use of stock management has been shown to be an effective means of manipulating numbers of the grey field slug, Deroceras reticulatum (Muller). At stocking rates of 1500 sheep days/ha or more, slug control in excess of 90% can be achieved with the flexibility of employing various combinations of stock numbers and length of grazing period. In the same trials methiocarb slug baits applied at 10kg product/ha gave 50% control of slugs. A quantitative sampling technique was developed and is briefly described.

Mineral concentrations of soft tissue and bone were measured in carcasses from cattle slaughtered serially across a wide weight range. Seventy-four small framed Angus steers and 71 Holstein steers were selected to represent diverse mature types. Cattle were individually fed ad libitumeither a maize grain or maize silage diet, housed inside a barn or in outside pens and slaughtered over five weights within breed. After slaughter, a half-carcass was separated into soft tissue (lean and fat) and bone. Tissues were ground, freeze-dried and K, P, Ca, Mg, Na, Fe, Cu, Zn and Mn were measured. Concentrations of minerals were analysed by covariance analysis, using carcass weight as a covariate.

The relationships between carcass weight and concentrations of all soft tissue minerals except Na and Zn were not affected by diet, breed or type of housing. Concentration of Na decreased with increasing carcass weight and at a slower rate in soft tissue of grain-fed cattle than in soft tissue of silage-fed cattle. Concentration of Zn increased with increased carcass weight in Angus, while in Holsteins it decreased. Soft tissue of Angus and Holsteins had similar concentrations of Fe and Mn. Holsteins had higher concentrations of the other minerals in soft tissue than Angus, possibly because they were at an earlier stage of maturity at the same carcass weight. Carcass weight had no effect on K, Ca, Fe or Cu content of soft tissue.

Diet influenced concentrations of P, Ca and Na in bone and affected the relationship of bone Fe to carcass weight. Due to their later stage of maturity at the same carcass weight, Angus had less K and more Ca, Na and Zn in bone than Holsteins. Carcass weight had no influence on K, P, Mg, Na, Cu or Mn content of bone.

These data provide baseline values for future studies, show that breed mature size differences in mineral concentrations of soft tissue and carcass bone may exist and that diet may influence concentration of soft tissue Na and some bone minerals.

Five rumen-cannulated dairy goats were fed diets supplying 2·8 g P/day plus 1·4 g P/kg milk (adequate P) for weeks 1–6 of lactation. Two goats then continued to receive this adequate P supply while three goats were fed deficient diets supplying only 0·8 g P/day plus 0·4 g P/kg milk. Solutions containing CrEDTA and (15NH4)2SO4 were infused into the rumen continuously for 96 h during weeks 5–6 and 11–12, respectively. At intervals following the intraruminal infusion, 15N enrichments of rumen ammonia-N, rumen bacteria-N and milk protein-N were determined. Cr concentration was measured in particle-free rumen fluid.

P deficiency did not significantly affect rumen fluid kinetics. It caused a significant increase in pH and reduced the size of the rumen ammonia pool and its outflow rate. Digestibility of organic matter as well as efficiency of microbial protein synthesis were decreased significantly and thus net microbial yield was reduced from 34·1 to 13·7 g N/day. The transfer of N of microbial origin to milk protein decreased from 5·3 to 2·7 g/day, whereas secretion of N in milk protein not originating from rumen microbes remained unchanged at 5·6–5·8 g/day.

Pre-emergence herbicides applied at field recommended doses, 3 days after transplanting (DAT) rice plants, inhibited growth and N2-fixation of Azolla pinnata (Bangkok) and BGA (blue-green algae) inoculated 10 DAT. This inhibition was up to 15 DAT in Azolla and up to 20 DAT in BGA. Butachlor and Oxadiazon resulted in higher toxicity to Azolla and BGA than Benthiocarb and Pendimethalin. The application of 0·5 kg/ha active ingredient of 2,4-DNa did not inhibit growth of Azolla but inhibited BGA growth. However, 2,4-DEE, a post-emergence herbicide, applied 30 DAT showed inhibitory effects on the growth and N2-fixation of both Azolla and BGA. Inoculation of 2·0 t/ha of fresh Azolla 10 DAT produced maximum biomass within 20–25 days of herbicide treatments, depending upon the season. The inoculation of 10 kg/ha of a dry mixture of BGA 10 DAT could produce the maximum biomass 60 and 80 DAT in control and herbicide treated plots, respectively. The biomass and nitrogen produced by Azolla recorded at maximum mat formation were similar in both herbicide treated and untreated plots, but in BGA these were higher in controls than those of herbicide treated plots.

The use of Azolla and BGA biofertilizers along with herbicides increased the grain and straw yields, and panicle number and nitrogen uptake, by rice over no Azolla or BGA treatments. The Azolla and BGA treatments even without weeding increased rice yield up to that of herbicide and biofertilizer treatments.

There has been little study on the growth and morphology of individual plants constituting the population of white clover in mixed swards under grazing. Such information is required if the mechanisms governing plant productivity and persistence are to be understood.

Intact white clover plants were sampled from intensively sheep-grazed pastures under set stocking, rotational grazing, and a combination of both systems, by taking turves (250 × 250 mm), and washing out the plants, every month for a year. Characters measured for every stolon of each plant were: presence of a growing point; numbers of leaves, roots and axillary buds; stolon length. Total plant leaf and stolon dry weight were also recorded. Plants were classified according to degree of branching, and the contribution of each branching order to the population determined.

There were strong seasonal variations in plant size (leaf and stolon dry weight, stolon length, and numbers of stolons and leaves per plant) which showed a significant decrease in spring with recovery over the following summer. This was paralleled by a rapid increase in the proportion of less branched plants (1st and 2nd branching order) in the population from 60 to 80% in spring, as higher-order plants broke up into smaller- and lower-ordered plants at this time. Numbers of roots per plant increased over winter to peak in early spring then declined in the following summer-autumn. While system of grazing management had no significant effect on branching structure of plants, it had a large effect on plant dry weight; rotationally grazed plants were 2·5 times larger than set stocked plants (0·182 cf. 0·073 g respectively).

Other general features of plant morphology were that each successive order of branch stolons was shorter and length before branching was less than that of their preceding parent stolon. The highest branching order observed was 6th order. There was no relationship between branching and numbers of roots; in branched plants only 55% of stolons were rooted regardless of plant order, but rooted stolons accounted for 85% of total stolon length and carried 62, 48 and 90% of the leaves, growing points and axillary buds per plant, respectively.

Comparison with other studies suggests that the processes outlined in this report may be common to white clover growth under grazing over a wide range of favourable environments.

In a greenhouse experiment, the effect of soil sodicity (exchangeable Na percentage 3, 10, 20, 40 and 60) and Zn (0 and 10 mg Zn/kg soil) on soil solution chemistry of Mn was investigated under submerged conditions. Calculated amounts of NaHCO3 were added to Typic Ustifluvent sandy loam soil to obtain required sodicity levels. The soil solutions collected under the atmosphere of N2 gas by gravity were analysed for pH, pE, EC and Mn. Soil submergence decreased pH and pE, and increased Mn concentrations in all the treatments. Maximum Mn concentration was obtained at 14-day submergence. Increasing sodicity levels increased soil solution pH and decreased Mn concentrations. A significant negative correlation (r = -0·74**) was observed between soil solution Mn and pH. Despite large variations in pH, pE, ionic strength and Mn concentration in soil solution, the values of expressions: pH+½log Mn2+ + ½log Pco2 and pMn+2pOH were fairly constant and close to the theoretical values of 4·4 and 17·2 respectively, indicating that the MnCO3-Mn2+ system regulated the solubility of Mn2+ in the sodic soils. Addition of ZnSO4 did not have appreciable effects on the soil solution pH, Mn and solid phases of Mn.