Relative efficiency of ammonium polyphosphate and orthophosphates for wheat and their residual effects on succeeding cowpea fodder

The relative efficiency of ortho and polyphosphates as P sources for wheat were studied in a field experiment with five sources—TSP, DAP, NP, APP (solid) and APP (Liquid) at three levels—13, 26 and 39 kg P ha^–1 and the residual effect was studied on a succeeding cowpea (fodder). Both the crops were grown each year at same location. Wheat responded upto 39 kg P ha^–1 in the first year but only upto 26 kg P ha^–1 in the second year. The growth parameters—plant height and dry matter production and yield attributes-ears m^–1, grains ear^–1 and test weight were favourably influenced by P application. The rate of P uptake initially exceeded the dry matter production. Wheat when fertilized with 26 or 39 kg P ha^–1 left behind a significant residual effect to raise the soil P availability and dry matter yield of cowpea. The grain yield of wheat was higher with APP's than with NP or DAP but the residual effect was the highest with NP. The magnitude of build up of soil available P with NP and APP's were similar and higher than DAP or TSP.     

Effect of green manure on the yield,N uptake and floodwater properties of a flooded rice,wheat rotation receiving15N urea on a highly permeable soil

Field studies were conducted for two years on a rapidly percolating loamy sand (Typic Ustochrept) to evaluate the effect of green manure (GM) on the yield,¹⁵N recovery from urea applied to flooded rice, the potential for ammonia loss and uptake of residual fertilizer N by succeeding crops. The GM crop ofSesbania aculeata was grownin situ and incorporated one day before transplanting rice. Urea was broadcast in 0.05 m deep floodwater, and incorporated with a harrow. Green manure significantly increased the yield and N uptake by rice and substituted for a minimum of 60 kg fertilizer N ha^–1. The recovery of fertilizer N as indicated by¹⁵N recovery was higher in the GM + urea treatments. The grain yield and N uptake by succeeding wheat in the rotation was slightly higher with GM. The recovery of residual fertilizer N as indicated by the¹⁵N recovery in the second, third and fourth crops of wheat, rice and wheat was only 3, 1 and 1 per cent of the urea fertilizer applied to the preceding rice crop. Floodwater chemistry parameters showed that the combined use of the GM and 40 kg N ha^–1 as urea applied at transplanting resulted in a comparatively higher potential for NH₃ loss immediately after fertilizer application. The actual ammonia loss as suggested by the¹⁵N recoveries in the rice crop, however, did not appear to be appreciably larger in the GM treatment. It appeared the ammonia loss was restricted by low ammoniacal-N concentration maintained in the floodwater after 2 to 3 days of fertilizer application.     

Response of sorghum to fertilizer phosphorus and its residual value in a Vertisol

The response of crops to added P in Vertisols is generally less predictable than in other soil types under similar agroclimatic conditions. Very few studies have considered the residual effects of P while studying responses to fresh P applications. Field experiments were conducted for three years to study the response of sorghum to fertilizer P applied at 0, 10, 20 and 40 kg P ha^–1, and its residual value in a Vertisol, very low in extractable P (0.4 mg P kg^–1 soil), at the ICRISAT Center, Patancheru (near Hyderbad), India. In order to compare the response to fresh and residual P directly in each season, a split-plot design was adopted. One crop of sorghum (cv CSH6) was grown each year during the rainy season (June-September).The phenology of the sorghum crop and its harvest index were greatly affected by P application. The days to 50% flowering and physiological maturity were significantly reduced by P application as well as by the residues of fertilizer P applied in the previous season. In the first year of the experiment, sorghum grain yield increased from 0.14 t (no P added) to 3.48 t ha^–1 with P added at the rate of 40 kg P ha^–1. Phosphorus applied in the previous year was 58% as effective as fresh P but P applied two years earlier was only 18% as effective as fresh P.     

Phosphorus management in continuous wheat and wheat-legume rotations

The sustainability of cropping systems is closely related to the judicious use of fertilizers. Little research has been conducted on the management of P in rotations in Morocco. The purpose of this study was to determine the effects of direct, cumulative, and residual P on wheat (Triticum aestivum) and chickpea (Cicer arietinum L.) yields under field conditions in two cropping systems: continuous wheat (W-W) and chickpea-wheat (CP-W). Experiments were conducted in 1994–96 at two locations in the arid and semiarid regions of Morocco. Phosphorus was applied the first year at rates of 0, 9, 18, and 27 kg P ha^–1 on both wheat and chickpea. The second year, plots were split into treatments with P and without P fertilizer. The changes in NaHCO₃-P in soil showed that after two years of cropping, P rates of 9 and 18 kg P ha^–1 were needed to increase and maintain soil test P level in the range where a third successive crop could be grown without fertilization at locations 1 and 2, respectively. Also, soils with the same initial NaHCO₃-P soil test levels required different amounts of fertilizer P to produce maximum yields. Inclusion of chickpea in the rotation resulted in a greater response to residual P by wheat at location 2. Differences in wheat grain yield between rotations were not significant. The maximum increase in yields above the nil-P treatment due to the highest amount applied in the the previous year was 1.3 t ha^–1, obtained for continuous wheat at location 2. Though the residual P effect was evident in this study, it did not produce maximum yields. Yields (GY, DM) could be predicted by the inclusion of both P applied in previous year (PR) and P applied in the current year (CP) by the following model: GY or DM = a + b*Ln(RP+1) + c*Ln(CP+1). Based on the range of P rates used in this study, a single P application for a 2-year rotation is not a suitable practice in these soils. The application of 18 kg P ha^–1 each year is recommended for continuous wheat, and 9 kg P ha^–1 the first year plus 18 kg P ha^–1 the second year is recommended for chickpea-wheat rotations. We suggest that either using single large applications of P or performing repeated applications should take into account the range of targeted application rates.     

Long-term effect of N and P fertilization on a pearlmillet—wheat cropping system

Results of an eight-year study on long-term effect of N and P application in a pearlmillet—wheat sequence is reported. There was little or no residual effect of N on any of the crops. Pearlmillet needed 70 to 80 kg N and wheat required more than 120 kg N ha^–1 every year for optimum grain yield. There was no soluble P build up in soil by continuous P application. Fertilizing wheat every year with 19 kg P and pearlmillet with 13 kg P ha^–1 is considered optimum.Continuous cropping leading to a production of 216 tonnes of biomass ha^–1 in 17 crops and use of high analysis N (urea) and P (triple superphosphate) fertilizers had not impaired the K and Zn supplying capacity of these alluvial soils containing illite clay minerals. The experiment is being continued to monitor the productivity of the soil as affected by continuous cropping.     

Transformations of residual fertilizer P in a semi-arid tropical soil under eight-year peanut-wheat rotation

Long-term transformations of residual phosphorus (P) governs the availability of phosphorus to crops. Very limited information is available on the transformations of residual fertilizer P in semi-arid tropical soils under long-term crop rotations. Therefore, using sequential phosphorus fractionation procedure, we studied changes in labile and stable forms of inorganic and organic P in a semi-arid alluvial soil (Typic Ustisamments) after eight years of annual fertilizer P application either to one crop (alternate) or to both crops (cumulative) in a peanut (Arachis hypogaea) — wheat (Triticum aestivum) rotation.Total residual fertilizer P in soil (P recovered from P-fertilized minus control plots) ranged from 62 to 176 mg P kg^–1. In the alternate P treatments (P applied to peanut or wheat only), on an average of 3 rates of applied P (13, 26 and 39 kg P ha^–1), in surface (0–15 cm) and subsurface (15 to 30 cm) soil, respectively, residual fertilizer P consisted of 14.8 and 2.2% resin-P, 8.6 and 2.8% NaHCO₃-P, 6.3 and 0% microbial-P, 31.4 and 4.2% NaOH-P, 7.8 and 3.0% aggregate protected-P, 12.5 and 3.0% HCl-P, 3.4 and 0% H₂SO₄-P. The corresponding values for surface and subsurface soils of cumulative P treatments (P applied to both peanut and wheat) were: 12.8 and 1.6% resin-P, 6.9 and 2.3% NaHCO₃-P, 4.7 and 0% microbial-P, 32.5 and 4.2% NaOH-P, 5.6 and 2.0% aggregate protected-P, 14.8 and 3.8% HCl-P, 6.7 and 2.1% H₂SO₄-P. Considerable lower values for the 15–30 cm depth indicate only a very small movement of residual P to the subsoil.Significantly lower amount of fertilizer P (28% and 44%) found in labile (resin, NaHCO₃ and microbial P) and semi-labile (NaOH and sonicated NaOH P) fractions for the cumulative P treatment than alternate P treatment (35 and 46%, respectively) suggests that increased rates and frequency of applied P tend to enhance the conversion of residual P to stable forms which are less available to plants. About 12 to 19% of residual fertilizer P found as organic P in labile and semi-labile forms confirmed that organic P increased with long-term fertilizer management. In conclusion, the results of our study suggest that the alternate application of fertilizer P to a crop, as is shown for wheat, helps reduce the transformations of residual P to stable P forms.     

The value of poultry manure for wetland rice grown in rotation with wheat

Poultry manure applied alone or in combination with urea at different N levels was evaluated as a N source for wetland rice grown in a Fatehpur loamy sand soil. Residual effects were studied on wheat which followed rice every year during the three cropping cycles. In the first year, poultry manure did not perform better than urea but by the third year, when applied in quantities sufficient to supply 120 and 180 kg N ha^–1, it produced significantly more rice grain yield than the same rates of N as urea. Poultry manure sustained the grain yield of rice during the three years while the yield decreased with urea. Apparent N recovery by rice decreased from 45 to 28% during 1987 to 1989 in the case of urea, but it remained almost the same (35, 33 and 37%) for poultry manure. Thus, urea N values of poultry manure calculated from yield or N uptake data following two different approaches averaged 80, 112 and 127% in 1987, 1988 and 1989, respectively. Poultry manure and urea applied in 1:1 ratio on N basis produced yields in between the yields from the two sources applied alone. After three cycles of rice-wheat rotation, the organic matter in the soil increased with the amount of manure applied to a plot. Olsen available P increased in soils amended with poultry manure. A residual effect of poultry manure applied to rice to supply 120 or 180 kg N ha^–1 was observed in the wheat which followed rice and it was equivalent to 40 kg N ha^–1 plus some P applied directly to wheat.     

The effect of fertilizer placement on nitrogen uptake and yield of wheat and maize in Chinese loess soils

Field trials were carried out to study the fate of¹⁵N-labelled urea applied to summer maize and winter wheat in loess soils in Shaanxi Province, north-west China. In the maize experiment, nitrogen was applied at rates of 0 or 210 kg N ha^–1, either as a surface application, mixed uniformly with the top 0.15 m of soil, or placed in holes 0.1 m deep adjacent to each plant and then covered with soil. In the wheat experiment, nitrogen was applied at rates of 0, 75 or 150 kg N ha^–1, either to the surface, or incorporated by mixing with the top 0.15 m, or placed in a band at 0.15 m depth. Measurements were made of crop N uptake, residual fertilizer N and soil mineral N. The total above-ground dry matter yield of maize varied between 7.6 and 11.9 t ha^–1. The crop recovery of fertilizer N following point placement was 25% of that applied, which was higher than that from the surface application (18%) or incorporation by mixing (18%). The total grain yield of wheat varied between 4.3 and 4.7 t ha^–1. In the surface applications, the recovery of fertilizer-derived nitrogen (25%) was considerably lower than that from the mixing treatments and banded placements (33 and 36%). The fertilizer N application rate had a significant effect on grain and total dry matter yield, as well as on total N uptake and grain N contents. The main mechanism for loss of N appeared to be by ammonia volatilization, rather than leaching. High mineral N concentrations remained in the soil at harvest, following both crops, demonstrating a potential for significant reductions in N application rates without associated loss in yield.     

Phosphorus response of grain sorghum in the Guinea savanna of Nigeria as influenced by rates,placement and plant spacing

Improved grain sorghum (Sorghum bicolor L.) Moench responded to applied P up to 22 kg P ha^–1 on an Alfisol situated in the Nigeria savanna. Hill placement of phosphorus fertilizer gave higher grain yield of sorghum, one thousand grain weight, P content of leaves and residual phosphate than furrow P application. Grain yields were observed to be higher at population of 55 555 plants ha^–1 than at 31 750 and 24 700.     

Yield response of lentil to directly applied and residual phosphorus in a Mediterranean environment

The response of lentil grown under rainfed conditions to directly applied and residual phosphorus (P) was described by a modified Mitscherlich equation, accounting for the effects of rainfall on (1) potential yield, and (2) the availability of soil-P to the crop. The response of lentil yield to directly applied and residual P was studied in two-course cereal–lentil rotational trials under rainfed conditions in a Mediterranean-type environment. Cereal crops were grown at different P application rates during 4 growing seasons at 3 sites, representing different rainfall zones in northwest Syria. Lentil (Lens culinaris Med.) was grown during 4 seasons at the same sites, each lentil crop following a cereal crop. In 3 out of 4 lentil-growing seasons, additional P was applied to lentil in subplots to compare the residual and direct effects of P application. The initial contents of extractable soil-P (P-Olsen) were low at all sites, in the range of 2–5 ppm P. Under the conditions of the experiments, lentil appeared to benefit slightly more from P applied to the preceding wheat crop (residual P) than from directly applied P. It is shown that the modified Mitscherlich equation could be used as a basis for P fertilizer recommendations for rainfed farming. As for lentil, it was concluded that a single application of P to the wheat crop in a wheat/lentil rotation could reduce the cost of lentil production, without reducing lentil yield.     

Response of maize (Zea mays) to phosphorus application on basaltic soils in Northwestern Cameroon

A field trial was conducted on two P sorptive, basaltic soils commonly used for maize production in Northwestern Cameroon. The objective was to determine the maintenance P rates required for adequate P supply in the soils for maize after initial capital dressing applications of P (0, 22, 44, 88 and 132 kg ha^-1) in 1991. These were followed by three supplementary P rates – 0, 44 and 88 kg ha^-1 in 1992. Three crops of maize (cv COCA) were grown to monitor the availability of the residual P. Experimental design was randomized complete block with four replications in 1991 and a split-plot in 1992 and 1993. The soils at the experimental sites were rich in organic P which formed 67% and 57% of total P at Mfonta and Babungo respectively. Laboratory P sorption studies indicated high P requirements by the basaltic soils used in the study. The amounts of P sorbed to attain 0.2 ug g^-1 in soil solution were 1200 ug g^-1 at Mfonta and 600 ug g^-1 at Babungo. In spite of these high P sorption capacities, significant responses to small rates of P application were observed. It was concluded that a sizable proportion of P released from organic P mineralization was used to satisfy P sorption capacity of the soils, resulting in maize response to small rates of fertilizer P application. Residual P effects on maize yield were related to applied P. Bray 1 extractable soil P was weakly related to grain yields (r = 0.136 at Mfonta and r = 0.186 at Babungo). A critical value of 5.5 mg kg^-1 Bray 2 extractable P in the soil was established for maize at Mfonta site. About 44 kg P ha^-1 was recommended for maize at this site when Bray 2 soil P test was below this critical value.     

Yield and P uptake by wheat as affected by residual and applied P

The effect of residual (built up in continued fertilizer experiments) and applied P in Fatehpur loamy sand and Jodhan sandy loam soils of two long term experiments on its availability and uptake by wheat (Triticum aestivum L.) was studied using³²P in greenhouse experiment. Dry matter yield increased significantly with carry over P. Response in the absence of residual P was observed up to a direct application of 134 kg P ha^?1, whereas, in the presence of carry over P, the response was confined upto 67 kg P ha^?1 at site A. The response was however, observed up to 67 kg P ha^?1 irrespective of carry over P at site B. Total P uptake by wheat was significantly increased at all levels of residual P. However, it did not differ signficantly among levels of residual P when these were high. The uptake of soil P (residual) increased signficantly with increase in the dose of directly applied P, indicating that addition of inorganic P fertilizer tends to mobilize the native soil P. Per cent utilization of fertilizer P was enhanced in soils having residual P from continuous application of both inorganic and organic P sources.     

Maintenance of Phosphorus Fertilizer and Residual Phosphorus Effect on Corn Production

Phosphorus (P) deficiency is invariably a common crop growth and yield-limiting factor in unfertilized soils, especially soils high in calcium carbonate, which reduces P solubility. Even when such soils are fertilized, adsorption and desorption lead towards a reversion to stable and less soluble P forms, thus reducing fertilizer use efficiency. Field trials that examine the implications of such P reactions and residual fertilizer P responses in the field are relatively rare in Mediterranean environments. A 5-year field experiment in southern Turkey examined the residual effects of repeated P fertilizer applications for corn production in a calcareous soil Typic Xerofluvent. Following the initial year's fertilization (0, 33, 66 and 99 kg P ha⁻¹) to establish a range of soil P levels in subsequent years, the main plots received 0, 9, 18, 27 and 36 kg P ha⁻¹ annually. Grain P uptake was calculated for each year and used in the prediction of P recovery. All plots were sampled and analyzed for available P prior to planting with a local corn hybrid. Soil P values increased with the initial P levels (8–24 mg kg⁻¹) but declined after 3 years (6–10 mg kg⁻¹). Only the lowest annual P application rate (9 kg P ha⁻¹) produced an available P level that was not in the sufficiency range. Grain yields across the main and subplots and years ranged from 6.6 to 13.2 t ha⁻¹. Overall corn yield averaged over the years increased by 8–33% compared to the control as the rates of applied P increased. However, P application had no effect in a year when below-average rainfall restricted crop growth. A residual P effect on grain yield occurred with higher P application levels in the last year. Leaf and grain P concentrations were in the sufficiency range in general. Grain P uptake was calculated for each year and used in the prediction of P recovery. Actual recovery was higher with low P application rates and ranged between 10.8 and 46.4%. The study indicated that under irrigated conditions, corn is likely to respond to P fertilization, but that buildup of available P can occur within a few years and adequate plant available P levels can be maintained by modest P fertilizer application rates.     

The residual effectiveness of previously applied copper fertiliser for grain yield of wheat grown on soils of south-west Australia

The residual effectiveness of copper (Cu) applied 18 to 21 years previously was estimated for grain yield of wheat. In one field experiment, current levels of Cu fertiliser were applied and its effectiveness was compared to that of the same level of Cu applied previously. The effects of nitrogen (N) fertiliser on the Cu concentration in the youngest emerged blade and in the grain, as well as the effects of N levels on the grain yield of wheat, were also studied.Where the recommended level of Cu fertiliser had been applied previously, its residual effectiveness depended on the soil type. On the grey sands over clay and gravelly sands over clay, the residual Cu would last approximately 20 years where wheat is grown in rotation with a legume crop (Lupinus augustifolius L.) and where N fertiliser is applied at high levels (92 kg N ha^–1). On the yellow brown sandy earths of the Newdegate district, the residual value was in excess of 30 years.When Cu levels in the soil are marginal, high levels of N applied to wheat crops grown on stubbles of legume crops (high soil N) could suffer from induce Cu deficiency which could reduce grain production.Critical concentrations of Cu in the youngest emerged blade of less than 1.2 mg Cu kg^–1 at Gs50–59 would indicate Cu deficiency. Cu concentrations of less than 1.1–1.2 mg Cu kg^–1 in the grain suggest that the wheat crop is marginally supplied with Cu. In both situations, Cu fertiliser needs to be applied before the next crop.     

Meat and bone meal as nitrogen and phosphorus fertilizer to cereals and rye grass

Meat and bone meal (MBM) contains appreciable amounts of total nitrogen (~8%), phosphorus (~5%) and calcium (~10%). It may therefore be a useful fertilizer for various crops. This paper shows results from both pot and field experiments on the N and P effects of MBM. In two field experiments with spring wheat, increasing amounts of MBM (500, 1000, 2000 kg MBM ha⁻¹) showed a linear yield increase related to the N-supply. A similar experiment with barley gave positive yield increase for 500 kg MBM ha⁻¹ and no further yield increase for larger amounts of MBM. Supply of extra mineral P gave no yield increase when 500 kg MBM ha⁻¹ or more was applied. Meat and bone meal as P fertilizer was studied in greenhouse experiments using spring barley and rye grass as test crops. N applications were 100 N kg ha⁻¹ to barley and 200 kg N ha⁻¹ to rye grass, either from mineral fertilizer or assuming that 80% of total N in MBM was effective. Four different P deficient soils were given increasing doses of MBM and compared with compound NPK fertilizer 11-5-18, mineral N fertilizer (0 kg P ha⁻¹) and a control (0 kg N ha⁻¹, 0 kg P ha⁻¹). In barley there was no significant yield difference between the NPK treatment and MBM treatment with equal N supply, and both had significant higher yield than the treatment receiving the same amount of mineral N without P-supply. The positive yield response of MBM was even larger in rye grass. Both in barley and rye grass a significant residual effect of P from MBM applied the year before was found when the treatments received the same amount of mineral N fertilizer (0 kg P ha⁻¹). The pot experiments confirmed the assumed N effect of MBM. When MBM is used according to the N demand of the crops, the P supply will be more than sufficient and residual P will be left in the soil. Since a part of this residual P was utilized by the crops of the following year, it is not recommended to apply P-fertilizer the year after MBM application.     

Nitrogen loss from different tillage systems and the effect on cereal grain yield

Grain yield, nitrogen (N) assimilation, ammonia (NH₃) volatilization, denitrification and fertilizer N distribution were examined in three commercially grown cereal crops; two were sown into conventionally tilled fields, while the third was direct drilled into an untilled field. The crops were top dressed with urea at establishment, tillering or ear initiation. Crop yield and N assimilation were measured in 16 m by 2.5 m plots receiving 0, 35, 70, 105, 140 or 175 kg N ha^–1. A mass balance micrometeorological technique was used to measure NH₃ volatilization, and other fertilizer N transformations and transfers were studied using¹⁵N labelled urea in microplots.On the conventionally tilled sites application of urea increased the grain yield of wheat from 3.9 to 5.5 t ha^–1, when averaged over the five application rates, three application times and two sites. There were no site or application time effects. However, on the direct drilled site, time of application had a significant effect on grain yield. When urea was applied at establishment, grain yield was not significantly increased and the mean yield (2.81 t ha^–1) was less than that obtained from treatments fertilized at tillering or ear initiation (4.09 and 4.0 t ha^–1, respectively). Much of the variation in grain yield at the no-till site could be ascribed to differences in NH₃ volatilization. At the no-till site, NH₃ losses were equivalent to 24, 12 and 1% of the N applied at establishment, tillering and ear initiation, respectively. Negligible volatilization of NH₃ occurred at the other sites. The surface soil at the no-till site had the highest urease activity and the soil was covered with alkaline ash resulting from stubble burning.Plant recovery of fertilizer N did not vary with application time on conventionally tilled sites (mean 62%). However, plant recovery of¹⁵N applied to the no-till site at establishment (35% of the applied N) was significantly less than that from plots where the application was delayed (45% at tillering and 55% at ear initiation, respectively). Leaching of N to below 300 mm depth was minimal (0 to 5% of the applied N). The calculated denitrification losses ranged from 1% to 14% of the applied N.The results show that the relative importance of NH₃ volatilization, leaching and denitrification varied with site and fertilization time. The importance of the various N loss mechanisms needs to be taken into account when N fertilization strategies are being developed.     

Wheat Responses in Semiarid Northern Ethiopia to N2 Fixation by Pisum Sativum Treated with Phosphorous Fertilizers and Inoculant

Nitrogen fixation (N₂) by leguminous crops is a relatively low-cost alternative to N fertilizers for smallholder farmers in Africa. Nitrogen fixation in pea (Pisum sativum L. cv. Markos) as affected by phosphorus (P) fertilization (0, 30 kg P ha⁻¹) and inoculation (uninoculated and inoculated) in the semiarid conditions of Northern Ethiopia was studied using the ¹⁵N isotope dilution method and locally adapted barley (Hordeum vulgare L. cv. Bureguda) as reference crop. The effect of pea fixed nitrogen (N₂) on yield of the subsequent wheat crop (Triticum aestivum L.) was also assessed. Phosphorus and inoculation significantly influenced nodulation at the late flowering stage and also significantly increased P and N concentrations in shoots, and P concentration in roots, while P and N concentrations in nodules were not affected. Biomass, pods m⁻² and grain yield responded positively to P and inoculation, while seeds pod⁻¹ and seed weights were not significantly affected by these treatments. Phosphorus and inoculation enhanced the percentage of N derived from the atmosphere in the whole plant ranging from 53 to 70%, corresponding to the total amount of N₂ fixed varying from 55 to 141 kg N ha⁻¹. Soil N balance after pea ranged from − 9.2 to 19.3 kg N ha⁻¹ relative to following barley, where barley extracted N on the average of 6.9 and 62.0 kg N ha⁻¹ derived from fertilizer and soil, respectively. Beneficial effects of pea fixed N₂ on yield of the following cereal crop were obtained, increasing the average grain and N yields of this crop by 1.06 Mg ha⁻¹ and 33 kg ha⁻¹, respectively, relative to the barley–wheat monocrop rotation. It can be concluded that pea can be grown as an alternative crop to fallow, benefiting farmers economically and increasing the soil fertility.     

Effect of phosphorus and potassium fertilizer on crop response and soil fertility in a long-term experiment

Data from 32 years of a rotation-fertility experiment were analyzed to determine the average P and K application rates required for maximum yield and for optimum yield. A four-year rotation of corn, soybean, wheat, hay was used for the first 10 years and then changed to corn-1, soybean, wheat, corn-2. Rates of P application per 4-year rotation ranged from 0 to 196 kg ha^–1 and for K from 0 to 558 kg ha^–1. Multiple regression equations were fitted to the mean yields per 4-year rotation for the response of each crop to P and K applications. The range in P application rates in kg of P per 4-year rotation required to get maximum yields of corn was 118 to 172, for soybeans was 134 to 150, and for wheat was 116 to 138. The range in K application rates in kg K per 4-year rotation to get maximum yields of corn was 378 to 411, for soybeans was 324 and 476, and for wheat was 11 to 323. For rates of application where P and K added exceeded crop removals, soil test P and K increased linearly with the cumulative positive balance of P and K. Where crop removal exceeded application rate, no relation was found between crop removal and soil test.Journal paper No. 10, 915 Purdue University Agric. Exp. Stn., West Lafayette, IN 47907. Contribution from the Department of Agronomy.     

Farm‐scale assessment of maize–pigeonpea productivity in Northern Tanzania

Little is known about productivity of smallholder maize–pigeonpea intercropping systems in sub-Saharan Africa. We conducted a survey of 277 farm households in Northern Tanzania to assess socio-economic factors, field management characteristics, and their association with productivity of maize–pigeonpea intercrops. On each farm, crop assessments were focused on a field that the farmer identified as most important for food supply. Variables associated with yields were evaluated using linear regression and regression classification. Biomass production ranged between 1.0 and 16.6 for maize, and between 0.2 and 11.9 t ha^?1 for pigeonpea (at maize harvest). The corresponding grain yields ranged between 0.1 and 9.5 for maize, and between 0.1 and 2.1 t ha^?1 for pigeonpea. Plant density at harvest, number of years the field had been cultivated, slope, weeding, soil fertility class, fertiliser and manure use were significantly associated with variation in maize grain yield, with interactions among the factors. Fields on flat and gentle slopes with plant density above 24,000 ha^?1 had 28% extra yields when fertiliser was applied, while less than 24,000 plants ha^?1 yielded 16% extra yield when manure was applied. Plant density at harvest was the key factor associated with pigeonpea yield; fields with densities above 24,000 plants ha^?1 yielded an average of 1.4 t ha^?1, while less than 24,000 plants ha^?1 yielded 0.5 t ha^?1. We conclude that performance of intercrops can be enhanced through application of organic and inorganic nutrient sources, and agronomic interventions including weeding, implementing soil conservation measures on steep slopes and optimising plant density.

     

Residual effects of growing mungbean and uridbean on the yield and nitrogen uptake of a succeeding wheat crop

A two year field experiment was carried out at the Indian Agricutural Research Institute, New Delhi - 110012, India to assess the effect of mungbean (Vigna radiata L.) and uridbean (Vigna mungo L.) residues on the yield and N uptake of a succeeding wheat crop as compared to sorghum fodder. Sorghum produced 3.5–7.5 times more dry matter and removed 2–3 times more nitrogen than mungbean or uridbean during same duration (80 ± 10 days) of their growth. Without N application the grain yield of wheat following mungbean and uridbean (without residue incorporation) was 0.45 and 0.48 t ha^–1 more than the yield of wheat following sorghum fodder. These yields were equivalent to that predicted when 36 and 38 kg urea-N ha^–1, respectively, was directly applied to wheat. The residual effects of these grain legumes were higher when succeeding wheat was fertilized with 60 kg urea-N ha^–1; at this level mungbean and uridbean spared 52 and 43 kg urea-N ha^–1, respectively, in succeeding wheat. The residual effect of mungbean and uridbean further increased when their residue was incorporated in soil; with this practice they spared 94 and 115 kg urea-N ha^–1, respectively, without N application to wheat and 74 and 82 kg urea-N ha^–1, respectively, with an application of 60 kg urea-N ha^–1 to wheat.Mungbean and uridbean, without residue incorporation, increased aboveground plant-N uptake of succeeding wheat by 11.5–34.9 and 10.8–34.0 kg N ha^–1, respectively; whereas with residue incorporation, they increased aboveground plant-N content of succeeding wheat by 26.1–45.8 and 32.7–47.7 kg N ha^–1, respectively.The results of the present study indicate that there is both an indirect sparing effect and a direct residual effect of mungbean and uridbean on the nitrogen needs of succeeding wheat, more so when their residues are incorporated in soil.