Turfgrass (Cynodon dactylon L.) sod production on sandy soils: II. Effects of irrigation and fertiliser regimes on N leaching

The effects of irrigation and fertiliser regimes on N leaching from the production of couch grass (Cynodon dactylon L.) sod, on a free-draining sandy soil, were evaluated in a 22-month field study. The experimental design used a randomised-block, split-plot design with three replicates. Main plots consisted of two irrigation treatments: 70 and 140% daily replacement of pan evaporation; four subplot fertiliser types (water-soluble (predominately NH₄NO₃), control-release, pelletised poultry manure and pelletised biosolids); and three N application rates (100, 200 and 300 kg N ha⁻¹ per crop). Nitrogen leaching was assessed by measuring the leachate volumes and concentrations of N species leached from soil lysimeters (250 mm in diameter by 950 mm in length) installed in 10 m² turfgrass plots. Nitrogen leaching ranged from 33 to 167 kg N ha⁻¹ over 22 months, depending upon the irrigation and fertiliser treatment. Irrigation treatment affected N leaching more than fertiliser treatment, and increasing the irrigation from 70 to 140% replacement of daily pan evaporation increased N leaching for all fertiliser types, and by up to four times. Forty six to 76% of losses occurred from the high irrigation treatments during the first 16 weeks after the turfgrass was planted as rhizomes. By contrast, N leaching did not appear to increase following harvest of sod. At the high irrigation treatment, N leaching was greater for the pelletised biosolids than the control-release; while at the low irrigation treatment, N leaching did not vary between fertiliser types. A significant proportion of the N leached was in the organic form. Therefore, we recommend total N and mineral N be measured when assessing N leaching from turfgrass. Nitrogen leaching from turfgrass production is low from all fertiliser types when the irrigation matches turfgrass water use and N is applied at a rate and frequency that approximates turfgrass requirements. Section Editor: P. J. Randall     

Nitrogen uptake in a Norway spruce stand following ammonium sulphate application,fertigation, irrigation,drought and nitrogen-free-fertilisation

The above-ground accumulation of N,N uptake and litter quality resulting from improved or deteriorated availability of water and nutrients in a 25 year old Norway spruce stand in SW Sweden (as part of the Skogaby project) is presented. Treatment include irrigation; artificial drought; ammonium sulphate addition; N-free-fertilisation and irrigation with liquid fertilisers including a complete set of nutrients according to the Ingested principle (fertigation). At start of the experiment the stand contained 86.5 t dry mass and 352 kg N ha⁻¹. The following three years the annual N uptake in untreated trees was 32 kg N ha⁻¹ to be compared with the annual N throughfall of 17 kg ha⁻¹. Simultaneously, the treatment with ammonium sulphate and liquid fertilisation resulted in 48 and 56 kg ha⁻¹ y⁻¹, respectively, in treatment specific N-uptake following an application of 100 kg N ha⁻¹ y⁻¹. Addition of a N-free fertiliser resulted in improved N-uptake by 19 kg N ha⁻¹ y⁻¹ and irrigation by 10 kg N ha⁻¹ y⁻¹, compared to control. A linear relation between total above-ground dry mass production and N-uptake was found for trees growing with similar water availability. Dry mass production increased with increased water availability given the same N-uptake. It is concluded that the studied stand this far is not N saturated', as N fertilisation resulted in both increased N uptake and increased growth. Addition of a N-free-fertiliser resulted in increased uptake of N compared to the control, indicating an increased mineralisation rate or uptake capacity of the root system. The linear relation between N uptake and biomass production shows that at this study site N is a highly limiting factor for growth.     

Effect of irrigation,plant density and fertilisers on yield and NPK uptake by groundnut

Summary Three levels of irrigation, three plant densities and three fertiliser schedules were tested in 3³ factorial confounded design with two replications in winter on sandy loam soils of Tirupati campus of Andhra Pradesh Agricultural University. Pod yield did not vary due to the plant densities and the fertiliser schedules when the crop was sown in optimum time during 1980. When the sowings were delayed, as in 1979, 444000 plants per ha and 60 kg N ha⁻¹, 40 kg P ha⁻¹ and 100 kg K ha⁻¹ was optimum. Scheduling irrigation at 25 or 50% DASM (depletion of available soil moisture) was optimum for the groundnut crop. There was no difference in the uptake of NPK due to irrigations at 25 and 50% DASM in both the years. Low plant density was as effective as high plant density for efficient use of fertilisers. Uptake of NPK by the crop was relatively high at higher fertiliser levels. However, this higher uptake did not contribute to high pod yield, probably due to utilisation of absorbed nutrients for rank vegetative growth.     

Basal fertiliser application method, tuber initiation nitrogen, foliar NPK and the tolerance of potatoes to infection by the potato cyst nematodes Globodera rostochiensis and G. pallida

The effects of broadcast granular, placed liquid and foliar fertilisers on the tolerance of potatoes to infection by potato cyst nematodes were investigated. The tolerance of the potato cv. Pentland Dell was not significantly improved by fertiliser application type but placed liquid fertiliser, with or without foliar applications, increased the concentrations of N, P and K measured in whole plant dry matter of PCN infected plants. The tolerance of the potato cv. Sante was not statistically improved by altering the balance of fertiliser nitrogen applications between planting and tuber initiation or by applying foliar nitrogen. Nitrogen applications of 120 kg N ha^-1 at planting and a further 120 kg N ha^-1 at tuber initiation supplemented with foliar N, however, achieved a larger tuber yield than the same nitrogen programme without foliar N and gave a significantly greater yield than the application of 240 kg N ha^-1 at planting plus foliar N. The emergence of both cultivars was delayed in the absence of oxamyl. N, P and K concentrations within whole plant dry matter were significantly higher in plants from oxamyl treated plots and both N and K concentrations were significantly increased by increasing the quantity of N at planting, at 56 DAP. Splitting the fertiliser N between planting and tuber initiation appears to be important in maintaining the availability of this nutrient to PCN infected plants throughout the season.     

Nitrogen contribution of cowpea green manure and residue to upland rice

Cowpea, Vigna unguiculata (L.) Walp., is well adapted to acid upland soil and can be grown for seed, green manure, and fodder production. A 2-yr field experiment was conducted on an Aeric Tropaqualf in the Philippines to determine the effect of cowpea management practice on the response of a subsequent upland rice crop to applied urea. Cowpea was grown to flowering and incorporated as a green manure or grown to maturity with either grain and pods removed or all aboveground vegetation removed before sowing rice. Cowpea green manure accumulated on average 68 kg N ha⁻¹, and aboveground residue after harvest of dry pods contained on average 46 kg N ha⁻¹. Compared with a pre-rice fallow, cowpea green manure and residue increased grain yield of upland rice by 0.7 Mg ha⁻¹ when no urea was applied to rice. Green manure and residue substituted for 66 and 70 kg urea-N ha⁻¹ on upland rice, respectively. In the absence of urea, green manure and residue increased total aboveground N in mature rice by 12 and 14 kg N ha⁻¹, respectively. These increases corresponded to plant recoveries of 13% for applied green manure N and 24% for applied residue N. At 15 d after sowing rice (DAS), 33% of the added green manure N and 16% of the added residue N was recovered as soil (nitrate + ammonium)-N. At 30 DAS, the corresponding recoveries were 20 and 37% for green manure N and residue N, respectively. Cowpea cropping with removal of all aboveground cowpea vegetation slightly increased (p<0.05) soil (nitrate + ammonium)-N at 15 DAS as compared with the pre-rice fallow, but it did not increase rice yield. Cowpea residue remaining after harvest of dry pods can be an effective N source for a subsequent upland rice crop.     

Long-term Effects of Pre-harvest Burning and Nitrogen and Vinasse Applications on Yield of Sugar Cane and Soil Carbon and Nitrogen Stocks on a Plantation in Pernambuco, N.E. Brazil

Since the 1970s the area under sugarcane in Brazil has increased from 2 million to over 5 million ha (M ha), and it is expected to pass the 7 M ha mark in 2007. More than half of the cane is harvested to produce bioethanol as a fuel for light vehicles. The distilleries produce approximately 13 L of distillery waste (vinasse) for each litre of ethanol produced. In the 1980s there was considerable concern over the long-term effects of the disposal of this material (containing about 1% carbon and high in K) on cane yields if it was applied to the field. At the same time there was a growing movement to abandon the practice of pre-harvest burning and some research was showing that some Brazilian varieties of sugar cane were able to obtain significant contributions of N from plant-associated biological nitrogen fixation (BNF). For these reasons an experiment was installed on a cane plantation in the state of Pernambuco, NE Brazil to investigate the long-term effects of vinasse and N fertiliser additions and the practice of pre-harvest burning on crop and sugar yield, soil fertility parameters, N balance and soil C stocks. The results showed that over a 16-year period, trash conservation (abandonment of burning) increased cane yields by 25% from a mean of 46 to 58 Mg ha⁻¹. Vinasse applications (80 m³ ha⁻¹ crop⁻¹) increased mean cane and sugar yield by 12 to 13% and the application of 80 kg N ha⁻¹ as urea increased cane yields by 9%, but total sugar yield by less than 6% (from 7.0 to 7.4 Mg ha⁻¹ crop⁻¹). The total N balance for the soil/plant system when only the surface 20 cm of the soil was considered was positive in plots where no N fertiliser was added. However, the data indicated that during the 16 years of the study considerable quantities of soil organic matter were accumulated below 20 cm depth such that the N balance considering the soil to 60 cm depth was strongly positive, except where N fertiliser was added. The data indicated that there were considerable BNF inputs to the system, which was consistent with its low response to N fertiliser and low N fertiliser-use-efficiency. There were no significant effects of vinasse or urea addition, or trash conservation on soil C stocks, although the higher yields proportioned by trash conservation had potentially significant benefits for increased mitigation of CO₂ emissions where the main use of the cane was for bioethanol production.     

Nitrogen-15 balances for urea and neem coated urea applied to lowland rice following two cowpea cropping systems

Little is known about whether the high N losses from inorganic N fertilizers applied to lowland rice (Oryza sativa L.) are affected by the combined use of either legume green manure or residue with N fertilizers. Field experiments were conducted in 1986 and 1987 on an Andaqueptic Haplaquoll in the Philippines to determine the effect of cowpea [Vigna unguiculata (L.) Walp.] cropping systems before rice on the fate and use efficiency of¹⁵N-labeled, urea and neem cake (Azadirachta indica Juss.) coated urea (NCU) applied to the subsequent transplanted lowland rice crop. The pre-rice cropping systems were fallow, cowpea incorporated at the flowering stage as a green manure, and cowpea grown to maturity with subsequent incorporation of residue remaining after grain and pod removal. The incorporated green manure contained 70 and 67 kg N ha⁻¹ in 1986 and 1987, respectively. The incorporated residue contained 54 and 49 kg N ha⁻¹ in 1986 and 1987, respectively. The unrecovered¹⁵N in the¹⁵N balances for 58 kg N ha⁻¹ applied as urea or NCU ranged from 23 to 34% but was not affected by pre-rice cropping system. The partial pressure of ammoniapNH₃, and floodwater (nitrate + nitrite)-N following application of 29 kg N ha⁻¹ as urea or NCU to 0.05-m-deep floodwater at 14 days after transplanting was not affected by pre-rice cropping system. In plots not fertilized with urea or NCU, green manure contributed an extra 12 and 26 kg N ha⁻¹, to mature rice plants in 1986 and 1987, respectively. The corresponding contributions from residue were 19 and 23 kg N ha⁻¹, respectively. Coating urea with 0.2g neem cake per g urea had no effect on loss of urea-N in either year; however, it significantly increased grain yield (0.4 Mg ha⁻¹) and total plant N (11 kg ha⁻¹) in 1987 but not in 1986.     

Effects of carbonized and dried chicken manures on the growth, yield, and N content of soybean

The present study was conducted to investigate the effects of nitrogen derived from dried or carbonized chicken manure on growth, nodulation, yield and N content of soybean. ¹⁵N labeled chicken manure used in this study was obtained from the droppings of chicken fed on hulled rice grown under field conditions and fertilized with ¹⁵N-labeled stable isotope ammonium sulphate and potassium nitrate fertilizers. Carbonized chicken manure was made by heat treatment in a muffle furnace in our laboratory. This study was conducted in pots filled with clay loam soil. Results from the study show that the application of carbonized chicken manure increased soybean seed yield by 23% and 43% for the 50 and 100 kg N ha⁻¹ rates respectively. Dried chicken manure application increased soybean seed yield by 7% and 30% for the 50 and 100 kg N ha⁻¹ rates respectively. There was no difference in the N manure yield of both manures when applied at the same rate. The percentage ¹⁵N recovery was 17.6% and 8.9% for carbonized chicken manure, 19.2% and 10.5% for dried chicken manure at 50 and 100 kg N ha⁻¹ rates respectively at peak flowering stage of soybean growth. We found high total nitrogen yields of soybean at the rate of 100 kg N ha⁻¹ for both manures. There was a positive relationship between number of nodules and seed yield of soybean. Total N content also showed positive relationship with number of nodules and seed yield of soybean. We supposed that the higher P content of carbonized chicken manure is responsible for the higher seed yield and nodule growth compared to dried chicken manure.     

Leaching loss of NO3-N and dissolved P from manure and fertilizer during turfgrass establishment

Cycling of manure nutrients through turfgrass sod could affect groundwater quality. The fate of nutrients in transplanted fertilizer- or manure-grown sod of Tifway bermudagrass (Cynodon dactylon L. Pers. X C. transvaalensis Burtt-Davey) was compared with that in composted dairy manure (CDM) applied to a sprigged treatment. Leaching loss of NO₃-N and dissolved P (DP) in filtrate (<0.45 μm) of leachate was compared among sodded and sprigged treatments during periods 0–50, 60–110, and 330–380 d after planting in lysimeters. In addition, recovery of N and P in turfgrass clippings and a sand medium was quantified. Maintenance applications of CDM or fertilizer P were top-dressed starting 60 d after planting. Leachate was collected and sampled over three simulated rain events during each of the three sampling periods. From 0 d to 50 d after planting, leaching loss of NO₃-N from sprigged Tifway totaled 2.0 g m⁻² and was 10 times greater than loss from CDM-grown or fertilizer-grown sod. In contrast, DP loss in leachate was ≤0.02 g m⁻² and similar among treatments. Surface applications of CDM and fertilizer P and N increased concentration and mass of total Kjeldahl N (TKN) and soil-test P (STP) in surface or subsurface layers of the sand medium. Yet, NO₃-N mass in leachate collected over three simulated rain events ranged from 0.0 to only 1.0% of applied N from 60–110 d and 330–380 d after planting. Leaching loss of NO₃-N did not differ between the sodded and sprigged treatments after two topdressings of CDM. Similarly, the DP mass recovered in leachate was small (≤0.013 g m⁻¹) and did not differ among treatments during the latter two sampling periods. The mass loss of DP in leachate was typically less than the DP mass applied through irrigation or simulated rain. Importing CDM in sod reduces NO₃-N leaching loss compared to sprigged turfgrass amended with CDM, but NO₃-N and DP leaching losses are similar during maintenance of CDM-grown and fertilizer-grown sod from 60–110 d to 330–380 d after transplanting. Responsible Editor: Bernard Nicolardot.     

Symbiotically fixed nitrogen from field- grown white and red clover mixed with ryegrasses at low levels of15N-fertilization

A field study was carried out near Zürich (Switzerland) to determine the yield of symbiotically fixed nitrogen (¹⁵N dilution) from white clover (Trifolium repens L.) grown with perennial ryegrass (Lolium perenne L) and from red clover (Trifolium pratense L.) grown with Italian ryegrass (Lolium multiflorum Lam.). A zero N fertilizer treatment was compared to a 30 kg N/ha per cut regime (90 to 150 kg ha⁻¹ annually). The annual yield of clover N derived from symbiosis averaged 131 kg ha⁻¹ (49 to 227 kg) without N fertilization and 83 kg ha⁻¹ (21 to 173 kg) with 30 kg of fertilizer N ha⁻¹ per cut in the seeding year. Values for the first production year were 308 kg ha⁻¹ (268 to 373 kg) without N fertilization and 232 kg ha⁻¹ (165 to 305 kg) with 30 kg fertilizer N ha⁻¹ per cut. The variation between years was associated mainly with the proportion of clover in the mixtures. Apparent clover-to-grass transfer of fixed N contributed up to 52 kg N ha⁻¹ per year (17 kg N ha⁻¹ on average) to the N yield of the mixtures. Percentage N derived from symbiosis averaged 75% for white and 86% for red clover. These percentages were affected only slightly by supplemental nitrogen, but declined markedly during late summer for white clover. It is concluded that the annual yield of symbiotically fixed N from clover/grass mixtures can be very high, provided that the proportion of clover in the mixtures exceeds 50% of total dry mass yield.     

Sustaining productivity of wheat–soybean cropping system through integrated nutrient management practices on the Vertisols of central India

Wheat–soybean is one of the most dominant cropping systems on the Vertisols of central India. Cultivation of durum wheat in winter season (November to April) has a considerable potential due to congenial climate, while soybean in rainy season (June to October) has witnessed a phenomenal growth in the last two decades in the region. Beside including a legume (soybean) in sequence with a cereal crop (wheat), combined use of available organic sources along with chemical fertilizers may prove beneficial for long-term productivity and sustainability of the system. A long-term experiment was conducted during 1995–2000 on the fine-textured Vertisols at Indore, India to study the effect of combined use of farmyard manure (FYM), poultry manure, vermicompost and biofertilizers (Azotobacter + phosphate solubilizing bacteria) with 0.5 and 1.0 NPK (120 kg N + 26.2 kg P + 33.3 kg K ha⁻¹) on wheat, and residual effect on following soybean. Grain yield of aestivum wheat in the initial 2 years and durum wheat in the later 3 years was significantly increased with 0.5 NPK + poultry manure at 2.5 t ha⁻¹ or FYM at 10 t ha⁻¹ compared with 0.5 NPK alone, and was on par with 1.0 NPK. However, the highest productivity was obtained when these organic sources were applied along with 1.0 NPK. Quality parameters of durum wheat viz protein content, hectolitre weight and sedimentation value showed improvement, and yellow berry content was significantly lower with combined use of NPK + organic sources compared with NPK alone and control. Soybean did not show much response to residual effect of nutrient management treatments applied to wheat. Wheat gave higher profit than soybean, particularly in the later years due to lower grain yields and market price of soybean. However, the superiority of FYM as well as poultry manure along with 1.0 NPK was evident on the overall profitability of the system. Various soil fertility parameters including chemical and biological properties showed conspicuous improvement over the initial status under the treatments of FYM and poultry manure. Sustainability yield index was maximum under 1.0 NPK, followed by 1.0 NPK + poultry manure or FYM. It was concluded that application of available organic sources, particularly FYM and poultry manure along with full recommended dose of NPK fertilizers to wheat was essential for improving productivity, grain quality, profitability, soil health and sustainability of wheat–soybean system.     

Influence of Azolla management on the growth,yield of rice and soil fertility

A field experiment conducted at Central Rice Research Institute, Cuttack, during three successive seasons showed that with the 120-day-duration variety Ratna two dual crops ofAzolla pinnata R. Brown (Bangkok isolate) could be achieved 25 and 50 days after transplanting (DAT) by inoculating 2.0 t ha⁻¹ of fresh Azolla 10 and 30 DAT respectively. One basal crop of Azolla could also be grown using the same inoculum 20 days before transplanting (DBT) in fallow rice fields. The three crops of Azolla grown—once before transplanting and twice after transplanting—gave an average total biomass of 38–63 and 43–64 t ha⁻¹ fresh Azolla containing 64–90 and 76–94 kg N ha⁻¹ respectively in the square and rectangular spacings. Two crops of Azolla grown only as a dual crop, on the other hand, gave 26–39 and 29–41 t ha⁻¹ fresh Azolla which contained 44–61 and 43–59 kg N ha⁻¹ respectively. Growth and yield of rice were significantly higher in Azolla basal plus Azolla dual twice incorporated treatments than in the Azolla dual twice incorporation, Azolla basal plus 30 kg N ha⁻¹ urea and 60 kg N ha⁻¹ urea treatments. Azolla basal plus 30 kg N ha⁻¹ urea and 60 kg N ha⁻¹ urea showed similar yields but Azolla dual twice incorporation was significantly lower than those. The different spacing with same plant populations did not affect growth and yield significantly, whereas Azolla growth during dual cropping was 8.3 and 64% more in the rectangular spacing than in the square spacing in Azolla basal plus Azolla dual twice incorporation and Azolla dual twice incorporation treatments.     

Improving fertiliser efficiency on calcareous and alkaline soils with fluid sources of P,N and Zn

Alkaline calcareous or sodic soils represent an important proportion of the world's arable soils and are important for cereal production. For calcareous soils in general, despite high applications of P fertiliser for many years, P deficiency in cereals is common. Field experiments were conducted to test the relative ability of granular (e.g. DAP, MAP and TSP) and fluid fertilisers to supply P to wheat on grey calcareous and red brown calcareous sandy loam soils (Calcixerollic xerochrepts). A pot experiment was also conducted with these soils and with two non-calcareous alkaline soils to investigate the effects of placement on the efficiency of fertiliser performance. In 1998, fluid and granular sources of P, N and Zn were compared in the field by banding below the seed at sowing. In 1999, MAP applied as granular, and technical grade MAP applied as fluid, were compared as sources of P in rate response experiments. First year results showed that fluid sources of P, N and Zn produced significantly more grain than the granular product. In the following year, fluid fertilisers were found to produce significantly higher response curves for shoot dry weight, grain yield and P uptake in grain. At a commercial rate of 8 kg P ha^–1, fluid fertiliser produced between 22% and 27% more grain than the granular product. Soil moisture and fertiliser placement effects are implicated in the higher efficiency of fluid fertilisers.     

Does N fertiliser regime influence N leaching and quality of different-aged turfgrass (Pennisetum clandestinum) stands?

The effects of N fertiliser regimes on N leaching and turfgrass quality during the establishment and maintenance of Kikuyu turfgrass (Pennisetum clandestinum (Holst. Ex Chiov)) were evaluated in a 24 month field study. Treatments included two turfgrass ages (established from 20 week or 20 year old turfgrass, the later included a 50 mm ‘mat’ layer), three N application rates (50, 100 or 150 kg N ha^?1 yr^?1) and three application frequencies (every 4 weeks, 4 applications per year, 2 applications per year); and included turfgrass plots that received no N fertiliser. Nitrogen leaching, measured using soil lysimeters, ranged from 35 to 69 kg N ha^?1 by the end of 24 months, and varied with turfgrass age, but not N fertiliser regime. Greatest N losses occurred during turfgrass establishment, with up to 50% of all N leached in the organic form. We recommend measuring both total N and mineral N when assessing N leaching from turfgrass. The quality of the older turfgrass was maintained using less N fertiliser than the younger turfgrass, while increasing N application frequency improved the consistency of turfgrass growth and colour.     

Increasing phosphorus supply in subsurface soil in northern Australia: Rationale for deep placement and the effects with various crops

Three field experiments involving wheat, lucerne or cotton were established at different sites in the semiarid cropping regions of northern Australia, to test whether the deep placement of P fertiliser improved P availability, compared to the conventional practice of placing the fertiliser beside or adjacent to the seed. At Mulga View, near St George in southern Queensland on a red Kandosol soil with a Colwell soil test value of 19 mg P kg soil⁻¹ in the top 10 cm, there was no response to 10 kg P ha⁻¹ applied in the 5–7 cm layer. However, increasing the depth of placement of 10 kg P ha⁻¹ from 5–7 to 10–15 cm resulted in increased shoot growth and grain yield of spring wheat (Triticum aestivum) by 43 and 30%, respectively. A further grain yield increase of 43% to 3.2 t ha⁻¹ resulted when the deep P rate was increased from 10 to 40 kg P ha⁻¹. At Roma, in southern Queensland, on a grey/brown Vertosol with a Colwell soil test value of 15 mg P kg soil⁻¹, there was no difference in the winter growth of lucerne (Medicago sativa) when P fertiliser had been applied at 5–7 cm depth at rates of 10 and 40 kg P ha⁻¹. Shoot dry matter yields were around 2 t ha⁻¹. However dry matter yields increased significantly to 2.6 and 3.7 t ha⁻¹ when 10 and 40 kg P ha⁻¹, respectively were applied at the 10–15 cm depth. The third experiment was carried out on a grey Vertosol at Kununurra in Western Australia. Significant increases in the yield of seed cotton (Gossypium hirsutum) occurred when 50 kg P ha⁻¹ was applied at depth (10–15 and 25–30 cm), compared with the conventional placement at 7–10 cm, with maximum yield response to deep placement occurring with DAP, and the minimal response with MAP. The cotton was grown on raised beds and the crop was irrigated according to district practice. The response to deep P at all sites was attributed to the rapid drying of the soil surface layers, reducing the availability of soil or fertiliser P in these layers. The deep fertiliser P remained available during the growing season and alleviated the P deficiency that appears to be a feature of these soils when the surface layers become dry.     

Effect of different nitrogen sources on growth,acetylene reduction activity ofAzolla pinnata and yield of rice

The effect of nitrogenous sources like ammonium sulphate (AS), prilled urea (U), urea super granule (USG) and farm yard manure (FYM) was studied on the fresh biomass (FB) and acetylene reduction activity (ARA) ofAzolla pinnata, R. Brown (Bangkok isolate), grown as a dual crop with rice, and rice yield in three successive seasons. Irrespective of the N-sources and seasons, the FB and ARA of Azolla were observed to be maximum on 14th day after Azolla inoculation (DAI). The different N-sources had significant effect on the ARA and to a lesser extent on the FB of Azolla. The treatment without fertilizer-N (control) exhibited highest ARA, FB and total N-content of Azolla. These were inhibited to a lesser extent by USG and FYM, though used at higher rates of 75 kg N ha⁻¹ and 90 kgN ha⁻¹ respectively, compared to that by AS and U, used at lower rates of 45kg N ha⁻¹ each.     

Effect of varying periods of inoculation ofAzolla pinnata R. Brown on its growth,nitrogen fixation and response to rice crop

Summary Inoculation of water fernAzolla pinnata R. Brown (Bangkok isolate) at the rate of 500kg fresh weight ha⁻¹ in rice fields at weekly intervals after planting in addition to 30 kg N ha⁻¹ as urea showed a decrease in its growth and N₂-fixation with delay in application. Use of Azolla up to 3 weeks after planting (WAP) during wet and 4 WAP during dry season produced significantly more grain yield than 30 kg N ha⁻¹, whereas its application upto one WAP produced more grain yield than 60 kg N ha⁻¹. Grain yield with Azolla applied at the time of planting was similar to that of 60 kg N treatment during the wet season. Higher grain yields in zero and one WAP Azolla treatments resulted due to increase in both number of panicles m⁻² and number of grains/panicle while the subsequent Azolla inoculations increased grain yield mainly by producing more number of grains/panicle. Dry matter and total N yields at maturity of rice crop were more with Azolla application upto 3 WAP during wet and 2 WAP during dry season while the reduction in sterility (%) was observed upto one WAP over 30 kg N ha⁻¹ during both seasons. Number of tillers m⁻² and dry matter production at maximum tillering and flowering were more than 30 kg N ha⁻¹ with the use of Azolla upto one WAP. Increased grain N yield was observed with the use of Azolla upto 4 WAP during two seasons whereas straw N yield increased upto one WAP during wet and 2 WAP during dry season.     

Seasonal accumulation and partitioning of nitrogen by lentil

Although wheat (Triticum aestivum L.) is the dominant crop of the semi-arid plains of Canada and the western United States, lentil (Lens culinaris Medik.) has become an important alternative crop. Sources and seasonal accumulation of N must be understood in order to identify parameters that can lead to increased N₂-fixing activity and yield. Inoculated lentil was grown in a sandy-loam soil at an irrigated site in Saskatchewan, Canada. Wheat was used as the reference crop to estimate N₂ fixation by the A-value approach. Lentil and wheat received 10 and 100 kg N ha⁻¹ of ammonium nitrate, respectively. Crops were harvested six times during the growing season and plant components analyzed. During the first 71 days after planting the wheat had a higher daily dry matter and N accumulation compared to lentil. However, during the latter part of the growing season, daily dry matter and N accumulation were greater for lentil. The maximum total N accumulation for lentil at maturity was 149 kg ha⁻¹. In contrast, wheat had a maximum N accumulation of 98 kg ha⁻¹ in the Feekes 11.1 stage, or 86 days after planting. The maximum daily rates of N accumulation were 3.82 kg N ha⁻¹ day⁻¹ for lentil and 2.21 kg N ha⁻¹ day⁻¹ for wheat. The percentage of N derived from N₂ fixation (% Ndfa) ranged from 0 at the first harvest to 92 % at final harvest. Generative plant components had higher values for % Ndfa than the vegetative components which indicates that N in the reproductive plant parts was derived largely from current N₂ fixation and lentil continued to fix N until the end of the pod fill stage. At final harvest, lentil had derived 129 kg N ha⁻¹ from N₂ fixation with maximum N₂-fixing activity (4.4 kg N ha⁻¹ day⁻¹) occurring during the early stages of pod fill. Higher maximum rates of N₂-fixing activity than net N accumulation (3.82 kg N ha⁻¹ day⁻¹) may have been caused by N losses like volatilization. In addition, lentil provided a net N contribution to the soil of 59 kg ha⁻¹ following the removal of the grain.     

Growing vetches (Vicia villosa Roth) in irrigated cotton systems: inputs of fixed N, N fertiliser savings and cotton productivity

We compared symbiotic N₂ fixation by winter forage legumes (clovers, medics and vetches) using the ¹⁵N natural abundance technique in three experiments. Vetches (Vicia spp.) were the most productive legumes, and woollypod vetch fixed (shoot+root) up to 265 kg N ha^–1 (mean 227 kg N ha^–1) during a 4–5 months period over winter and early spring. Balansa and Berseem clovers, and Gama medic were highly productive in the first experiment, but fixed significantly less N than woollypod vetch in the second experiment. A 6-year study (1997–2003) compared cotton (Gossypium hirsutum L.) systems with and without vetch, or with faba beans (Vicia faba L.) to assess the effects of these crops on cotton production. Woollypod vetch was grown either between annual cotton crops, or between wheat (Triticum aestivumL.) and cotton crops. Vetch added 230 kg N ha^–1 (174 kg fixed N ha^–1) to the soil when incorporated as a green manure. Faba bean shoot residues and nodulated roots contributed 108 kg fixed N ha^–1 to the soil, following the removal of 80 kg N ha^–1 in the harvested seed (meaned over three crops). Lablab (Lablab purpureus L. – summer-growing and irrigated) added 277 kg N ha^–1 (244 kg fixed N ha^–1) before incorporation as a green manure in the first year of the experiment. The economic optimum N fertiliser rate for each cropping system was determined every second year when all systems were sown to cotton. Cotton following cotton required 105 kg fertiliser N ha^–1, but only 40 kg N ha^–1 when vetch was grown between each cotton crop. Cotton following wheat required 83 kg fertiliser N ha^–1 but no N fertiliser was needed when vetch was grown after wheat (the highest yielding system). Cotton following faba beans also required no N fertiliser. The vetch-based systems became more N fertile over the course of the experiment and produced greater lint yields than the comparative non-legume systems, and required less N fertiliser. While no cash flow was derived from growing vetch, economic benefits accrued from enhanced cotton yields, reduced N fertiliser requirements and improved soil fertility. These findings help explain the rotational benefits of vetches observed in other regions of the world.     

Effects of herbicide chlorsulfuron on growth and nutrient uptake parameters of wheat genotypes differing in Zn-efficiency

Prunings of Calliandra calothyrsus, Grevillea robusta, Leucaena diversifolia and farm yard manure were applied each cropping season at 3 and 6 t dry matter ha⁻¹ to an Oxisol in Burundi. The field plots also received basal applications of nitrogen (N), phosphorus (P) and potassium (K). Application of the tree prunings or farm yard manure decreased the concentration of monomeric inorganic aluminium (Al) in soil solution from 2.92 mg Al dm⁻³ in the control plots to 0.75 mg Al dm⁻³ in the plots receiving 6 t ha⁻¹ Calliandra prunings. The other organic materials also decreased the concentration of monomeric inorganic aluminium in the soil solution. The lowered Al concentration led to a corresponding decrease in the percentage Al saturation of the 0–10 cm soil layer from 80% to 68%. Grain yields of maize and beans were strongly inversely related to the percentage Al saturation of the soil. This confirms that soil acidity was the main constraint to maize and beans production. The yield improvement was mainly attributed to the ameliorating effects of the organic matter application on Al toxicity. The nutrient content had less effect presumably because of fertilizer use. In the best treatments, the yield of maize increased from 0.9 to 2.2 t ha⁻¹ and the corresponding beans yield increased from 0.2 to 1.2 t ha⁻¹. A C Borstlap Section editor