Upland rice response to potassium fertilization on a Brazilian oxisol

Even though K is an essential nutrient, the response of upland rice to K fertilization under field conditions has not been adequately documented. This research was conducted to examine the influence of K fertilization on yield of upland rice (Oryza sativa L.). In the first three years, K was broadcast at rates of 0, 42, 84, 126 and 168 kg K ha^–1. In the last two years K was banded at rates of 0, 25, 50, 75 and 100 kg K ha^–1. The experiment was conducted on an Oxisol (Typic Haplustox) during five consecutive years. Potassium significantly increased grain yields and dry matter production but response varied from cultivar to cultivar and year to year. Drought and panicle neck blast played an important role in limiting upland rice yield response to K fertilization. Potassium application rates associated with maximum grain yield varied from 83 to 127 kg K ha^–1 when K was broadcast and from 47 to 67 kg K ha^–1 when K was banded. Previous broadcast K, favorable weather and blast resistant cultivars probably contributed to higher yields with K banding in the fourth and fifth growing seasons.     

Effect of urea management on yield and N use efficiency of lowland rice on an acid sulfate soil

Field experiments were conducted during 1988–1989 at two adjacent sites on an acid sulfate soil (Sulfic Tropaquept) in Thailand to determine the influence of urea fertilization practices on lowland rice yield and N use efficiency. Almost all the unhydrolyzed urea completely disappeared from the floodwater within 8 to 10 d following urea application. A maximum partial pressure of ammonia (pNH₃) value of 0.14 Pa and an elevation in floodwater pH to about 7.5 following urea application suggest that appreciable loss of NH₃ could occur from this soil if wind speeds were favorable. Grain yields and N uptake were significantly increased with applied N over the control and affected by urea fertilization practices (4.7–5.7 Mg ha^–1 in dry season and 3.0–4.1 Mg ha^–1 in wet season). In terms of both grain yield and N uptake, incorporation treatments of urea as well as urea broadcasting onto drained soil followed by flooding 2 d later were more effective than the treatments in which the same fertilizer was broadcast directly into the floodwater either shortly or 10 d after transplanting (DT). The¹⁵N balance studies conducted in the wet season showed that N losses could be reduced to 31% of applied N by broadcasting of urea onto drained soil and flooding 2 d later compared with 52% loss by broadcasting of urea into floodwater at 10 DT. Gaseous N loss via NH₃ volatilization was probably responsible for the poor efficiency of broadcast urea in this study.     

Response of lowland rice and common bean grown in rotation to soil fertility levels on a Varzea soil

Brazil has approximately 30 million hectares of lowland areas, known locally as Varzea, but very little is known about their fertility and crop production potential. A field experiment was conducted for three consecutive years to evaluate response of lowland rice (Oryza sativa L.) grown in rotation with common bean (Phaseolus vulgaris L.) on a Varzea (low, Humic Gley) soil. Rice was grown at low (no fertilizer), medium (100 kg N ha^–1, 44 kg P ha^–1, 50 kg K ha^–1, 40 kg FTE-BR 12 ha^–1), and high (200 kg N ha^–1, 88 kg P ha^–1, 100 kg K ha^–1, 80 kg FTE-BR 12 ha^–1 fritted trace element-Brazil 12 as a source of micronutrients) soil fertility levels. Green manure with medium fertility was also included as an additional treatment. Average dry matter and grain yields of rice and common bean were significantly (P < 0.01) increased with increasing fertilization. Across the three years, rice yield was 4327 kg ha^–1 at low fertility, 5523 kg ha^–1 at medium fertility, 5465 kg ha^–1 at high fertility, and 6332 kg ha^–1 at medium fertility with green manure treatment. Similarly, average common bean yield was 294 kg ha^–1 at low soil fertility, 663 kg ha^–1 at medium soil fertility, 851 kg ha^–1 at high fertility, and 823 kg ha^–1 at medium fertility with green manure treatment. Significant differences in nutrient uptake in bean were observed for fertility, year, and their interactions; however, these factors were invariably nonsignificant in rice.     

Response of upland rice to phosphorus in an Ultisol in the humid forest zone of West Africa

Phosphorus (P) deficiency is one of the major limiting factor for crop production in highly weathered soils in the humid tropics. Field experiments were conducted for two years (1992 and 1993) to determine P response and efficiencies of upland rice cultivars in an Ultisol, low in available P, in the forest zone of Cote d'Ivoire. The rice cultivars tested were selected from a large number of entries tested earlier for acidity tolerance.Grain yields of the cultivars were significantly increased by P application. There was little further response in grain yield at higher rates than 60 kg P ha^–1. The rice cultivars differed in agronomic and physiological P efficiencies and the efficiencies were higher at lower rates of P. The rooting depths of the cultivars were increased by application of P at the lowest application rate (30 kg P ha^–1).The results suggest that P fertilization of soil acidity-tolerant upland rice cultivars can significantly improve the productivity of the Ultisols.     

Twenty-five years of phosphate and potassium fertilization of a crop rotation

Effects of rate and placement of phosphate and potassium fertilizers was studied using a 4-year rotation of corn (Zea mays L.), soybeans (Glycine max L.), wheat (Triticum vulgare L.) and hay (later changed to corn). Yields increased with increased P until 22 kg P ha^–1 yr^–1 was applied. Yields increased with increased K applications to 140 kg K ha^–1 yr^–1. Broadcast P applications gave high yields than row applications. Crop response to P was affected more by soil P level than by application to the specific crop. Residual effect from K fertilizer applications did not last as long as the residual effect from P application. Soil tests for available P were closely correlated with rate of P application over the 25-year period. Soil tests for P were higher where P was banded where P was broadcast indicating less tie-up of P by the soil where less mixing occurred.Journal Paper No. 7910, Purdue University Agricultural Experiment Station.     

Phosphorus Mass Balances for Successive Crops of Fertilised Rainfed Rice on a Sandy Lowland Soil

Raising and sustaining rice yields in the rainfed lowlands requires an understanding of nutrient inputs and outputs. On sandy lowland rice soils, managing phosphorus (P) supply is a key factor in achieving increased yields and sustainable production. Phosphorus inputs, rice yields, and crop P uptake were used to quantify P requirements of rice: together with results on soil P fractions, P balance sheets were constructed over five consecutive cropping seasons on a sandy Plinthustalf near Phnom Penh, Cambodia. Grain yields ranged from 665 to 1557 kg ha⁻¹ with no added P. Average yields increased significantly with P fertiliser application over five consecutive crops by 117, 139 and 140% when the phosphate fertiliser was applied at 8.25, 16.5 and 33 kg P ha⁻¹, respectively. Without added P fertiliser, a net loss of 1.2 kg P ha⁻¹ per crop was estimated with straw return and 2.0 kg P ha⁻¹ per crop with straw removed from the field, whereas, with added P fertiliser, there was a net P gain in the soil of 5.6 or 9.5 kg ha⁻¹ per crop when straw was removed and returned to the soil, respectively. After one crop, the addition of P fertiliser significantly (P < 0.01) increased recovery in all soil P fractions. Across five successive crops, repeated application of 16.5 and 33 kg P ha⁻¹ rates resulted in progressive P accumulation in the soil, especially a labile NaOH–Po pool, but had no effect on yields and P uptake of rice. By contrast, 8.25 kg P ha⁻¹ per rice crop was generally adequate for grain yields of 2.5–3.0 t ha⁻¹ and to maintain soil P pools.     

Mineral nutrition of slash pine in subtropical australia. I. stand growth response to fertilization

Fertilization at plantation establishment and later age is often required to maximize stand growth of slash pine (Pinus elliottii) in subtropical Australia. A field experiment was conducted to examine stand growth response of slash pine in the first 11.5 years of plantation following (1) initial fertilization at plantation establishment with phosphorus (P) at 11, 22, 45 and 90 kg P ha^–1 which were either banded or broadcast in the presence or absence of basal fertilizers containing 50 kg nitrogen (N) ha^–1, 50 kg potassium (K) ha^–1 and 5 kg copper (Cu) ha^–1 and (2) additional application of 40 kg P ha^–1 at age 10 years.The initial P fertilization significantly increased the stand growth in the first 9.6 years. The P banded application was more effective in improving the stand growth than the P broadcast application. Application of the N, K and Cu basal fertilizers did not affect the stand growth. Overall, 53–73% of the variation in basal area and volume growth in the first 9.6 years was explained by the initial P fertilization, indicating that P deficiency was the major factor limiting the stand growth under the experimental conditions. Optimum plantation age, at which the maximum periodical annual increment (PAI) of basal area was obtained, increased from age 10.9 to 12 years when the initial P rate increased from 11 to 90 kg P ha^–1. Application of additional 40 kg P ha^–1 at age 10 years resulted in a further improvement in the stand growth at age 11.5 years. With 66% of the variation in basal area PAI between ages 9.6 and 11.5 years, 50% was explained by the initial P fertilization and 16% by the additional P applied at age 10 years. Similarly, 51% and 12% of the variation in volume PAI were attributed to the initial P fertilization and the additional P application, respectively. This highlights the need of refertilization with P on some established stands of slash pine at later ages.     

Effect of Straw Application on Rice Yields and Nutrient Availability on an Alkaline and a pH-neutral Soil in a Sahelian Irrigation Scheme

Like elsewhere in the Sahel, actual rice yields (3–5 t ha⁻¹) are far below yield potential (±8 t ha⁻¹) in an irrigation scheme in central southern Mauritania. Earlier studies showed that yields are especially low on alkaline soils due to N and P deficiency. We investigated the potential of rice straw application as a mean to improve yields and fertilizer efficiency on an alkaline soil (pH 8.2) and a pH-neutral soil (pH 6.2). Application of 5 t straw ha⁻¹ increased yields by 1.1 t ha⁻¹ on average, independent of soil type and fertilizer dose. Contrary to our study, similar studies in Asia showed little short-term effects of straw on yield and N uptake. Straw application improved N availability, but not P availability. The improved N availability was attributed to N mineralized from the straw, from increased mineralization of soil organic matter (SOM) with a low C:N ratio (< 7.2) and from increased mineral fertilizer N (urea) recovery efficiency. We deduced that improved N fertilizer recovery upon straw application was due to reduced nitrification–denitrification losses. On the alkaline soil, volatilization was important, but that process seemed unaffected by straw application. We hypothesize that the positive effects of straw application at our study site are due to low soil C content (< 43 g kg⁻¹) and low C:N ratio compared to most lowland rice soils in Asia.     

Growth and yield responses of dryland grain sorghum to nitrogen and phosphorus fertilization in a ferruginous tropical soil (Haplustalf)

Field trials were conducted during the 1980–82 seasons to study the response dryland sorghum to nitrogen and phosphorus fertilization in a ferruginous tropical soil. Treatments tested were factorial combinations of three rates of nitrogen (0, 60 and 120 kg N ha^–1) and four rates of phosphorus (0, 11, 22 and 33 kg P ha^–1). Grain and straw yields and yield components were enhanced by nitrogen fertilization in two out of three years. The optimum N rate for grain yield was 60 kg N ha^–1 while straw yield responded up to 120 kg N ha^–1. The optimum P rate for dryland sorghum was 11 kg P ha^–1. Both N and P enhanced grain weight per head, grain number, test weight and tillering significantly but it was only N which enhanced 1000-grain weight and flag leaf area. Dry matter productin was increased by N fertilization but not by P. There were no significant N × P interactions for any of the parameters studied. Dryland sorghum response to N and P fertilization was influenced by season, time of planting and rainfall distribution.     

Effects of fertilization on nutrient budget and nitrogen use efficiency of farmland soil under different precipitations in Northeastern China

Based on a consecutive 16-year field trial and meteorological data, the effects of fertilization on the nutrient budget and nitrogen use efficiency in farmland soil under different precipitation years were studied. With no fertilization treatment, the grain yield of maize was 3,520 kg ha⁻¹ (mean yield over 13 years). But the maximum yield increased to 7,470 kg ha⁻¹ when treated with mineral N, P and K fertilizers and recycled manure. The nutrient uptake also increased by twofold to threefold in NPKM treated field compared with that in the control treatment. The highest yields were obtained in years with normal precipitation, despite the different fertilization schemes. The lowest yields were obtained in drought or waterlogging years, which were 44.7–58.5% of the yields in years with normal precipitation. It also appeared that the deficits of N, P and K were greater in the years with proper precipitation than those in arid or flood years, because more production was removed from the field. Soil total N decreased significantly when treated with mineral fertilizer or recycled manure alone. The maximum deficit of soil total N was observed in control treatment (557 kg ha⁻¹) from 1990 to 2005. The N treatment resulted in a significant negative balance of P, due to the high yield of the crop in response to applied N. The application of NP or N to soils resulted in a greater negative K balance than that of the control. The greatest negative balance of total P and available P were obtained under the control and N treatment, and the highest deficit of soil total K and exchangeable K were obtained under NP treatment. We found that the rate of 150 kg N ha⁻¹ year⁻¹ was inadequate for maintaining soil N balance, and amendment of soil with organic source could not stop the loss of soil P and K. The applying rates of 150 kg N ha⁻¹ year⁻¹, 25 kg P ha⁻¹ year⁻¹, and 60 kg K ha⁻¹ year⁻¹ combined with 2–3 t ha⁻¹ organic manure were recommended to maintain soil fertility level. The nitrogen use efficiency (NUE) was greatly improved in the years with proper precipitation and balanced fertilization. Higher NUE and grain yields were achieved under NPK and NPKM treatments in years with normal precipitation. The results clearly demonstrated that both organic and mineral fertilizers were needed to increase crop production, improve NUE and maintain soil fertility level.     

Response of promiscuously nodulating soybean to N and P fertilization andBradyrhizobium inoculation in a ferruginous tropical soil (Haplustalf)

Field trials were conducted at Samaru, Nigeria over a three-year period (1986–88) to study the effects of N and P fertilization on the response of promiscuously nodulating soybean toBradyrhizobium japonicum inoculation in a ferruginous tropical soil. Phosphorus fertilization enhanced nodulation, while N fertilization had no consistent effect on nodulation. Both N and P increased dry matter production. Seed yields were not influenced by the application of N. However, P increased seed yields in two out of three years. Response of seed yield to P fertilization was significant up to 26.4 kg P ha^–1.Bradyrhizobium inoculation consistently enhanced nodulation while it increased seed yield in only one out of three years. Results demonstrate that P is an important nutrient for soybean production in ferruginous tropical soils. The roles of promiscuously nodulating soybean in the maintenance of tropical soil fertility are discussed.     

Effect of split application of phosphorus on the growth ofAzolla and low land rice

TheAzolla pinnata (Vietnam) inoculated in rice field 10 days after transplanting (DAT) at a rate of 500 kg ha^–1 fresh biomass along with phosphorus fertilizer application produced a mat on the water surface at 30 DAT. The three split application of phosphorus as 4.4, 2.2 and 2.2 kg P ha^–1 applied at 10, 15 and 20 DAT, respectively produced 67% more biomass and 57% more Nitrogen inAzolla than those obtained by applying 8.8 kg P ha^–1 at 10 DAT. Whereas, the two splits of phosphorus as 6.6 and 2.2 kg and 4.4 and 4.4 kg P ha^–1 applied 10 and 15 DAT, respectively produced 20 and 33% more biomass and 14 and 27% more Nitrogen only.The three split application of phosphorus also increased the grain and straw yields, panicle number and weight, nitrogen concentration and its uptake in rice significantly over application of the entire amount once only. An increase of 10% grain yield and 13% straw yields was observed when 8.8 kg P ha^–1 was applied in three splits rather than applied at one time. On the average an increase of 24% grain and 23% straw yields in rice were observed due toAzolla intercropping and 22% and 16%, respectively due to phosphorus application. The intercropping ofAzolla with rice along with phosphorus application also increased the fertility level of soil by increasing the total nitrogen, organic carbon and available phosphorus of soil.     

Fertigation versus broadcasting in an orange grove

A long-term experiment was carried out in a mature orange grove comparing broadcasting versus continuous application of nitrogen at three rates (80, 160, 280 kg ha^–1), 22 kg P ha^–1 and 126 kg K ha^–1 annually. The trees were irrigated with minispriklers wetting 70% of the soil area.The level of NO₃-N in the leaves varied according to the rate of N application. Leaf K and P content were not affected by fertilization. High N applications caused excess N in the soil solution. The rate of N application did not affect orange yield, fruit size or quality. Fertigation at 160 kg N ha^–1 caused higher yields than when the same amount of fertilizer was broadcast. At the high application rate, no differences between modes of application were found.This study was initiated by A. Bar-Akiva, who died suddenly early in 1986. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No 2104-E, 1987 series.(deceased)     

The effect of broadcast P applications and small amounts of fertilizer placed with the seed on continuously cropped corn (Zea mays L.)

The response of corn (Zea mays L.) to broadcast P applications and to small amounts of fertilizer placed with the seed (fws) was measured in three field trials conducted for 10 years. Five rates of P (0, 11, 22, 45, and 90 kg ha^–1 yr^–1) were applied with and without 4.0-6.4-3.2 kg N, P, K ha^–1 placed with the seed (fws) in a factorial arrangement of treatments. The fws treatment delayed emergence at all sites, reduced final emergence at two of the three sites, increased seedling dry weights at the 4 to 6 leaf stage and reduced the time to 50% silking at two of the three sites. Ear moisture content at harvest was reduced by fws at all sites which indicated that fws advanced maturity. The fws treatment increased grain yield at two of the sites by 1.3 and 2.3%, respectively. Broadcast P applications increased seedling dry weight at all sites but decreased the time to 50% silking only at one site. Broadcast P decreased ear moisture content and increased grain yield at two sites. There was a significant fws by broadcast P interaction in the most P deficient soil such that response to broadcast P was lessened by fws. The interaction was strongest during the early stages of growth and decreased with maturity resulting in no fws by broadcast P interaction for grain yield.     

Urea rate and placement for maize production on a calcareous Vertisol

A study of urea N rate and placement for irrigated maize (Zea mays L) grown in Somalia was conducted to investigate this most promising and rather easily adopted cultural practice, in order to sharply increase present low yields. This work was done at the Afgoi station of the Agricultural Research Institute on a calcareous Vertisol. Six different levels of N (0, 20, 40, 80, 160 and 320 kg N ha^?1) as urea were used as main-plot treatments with four different placements as subplot treatments. Three of the placements consisted of broadcast-incorporated, broadcast-not incorporated, and sidedress on or in dry soil while the fourth placement was broadcast on wet soil. The grain yield response to added N was very highly significant and the regression analysis predicted a maximum yield of 7.6 t ha^?1 from 210 kg N ha^?1. A consistent yield depression occurred at the 320 kg N ha^?1 rate in all placement treatments. Placement of urea on or in dry soil gave significantly higher yields than did placement on the wet soil. The data indicate that substantial N losses occurred on this soil when urea was broadcast on a wet surface. The economic analysis to determine the feasibility of applying N to maize grown under improved crop production practices showed that fertilization with N can be very profitable. At the existing price for urea and value of maize, the economic optimum occurred at 164 kg N ha^?1 which gave a 2.1 t ha^?1 grain yield increase. This increased yield from N fertilization produced a profit of 1010 Somali shillings (US $162) ha^?1.     

Urea management for lowland transplanted rice as affected by application of farmyard manure

Farmyard manure (FYM) applied to rice-growing soils can substitute for industrial fertilizers, but little is known about the influence of FYM on the effectiveness and optimal management for industrial N fertilizers. A field experiment was conducted in northern Vietnam on a degraded soil in the spring season (February to June) and summer season (July to November) to determine the effect of FYM on optimal timing for the first application of urea. The experimental design was a randomized complete block with two rates of basal incorporated FYM (0 or 6 Mg ha^–1) in factorial combination with two timings of the first application of 30 kg urea-N ha^–1 (basal incorporated before transplanting or delayed until 14 to 16 d after transplanting). The FYM was formed by composting pig manure with rice straw for 3 months. Basal incorporation of FYM, containing 23 kg N ha^–1, increased rice grain yield in both seasons. The yield increase cannot be attributed to reduced ammonia loss of applied urea-N, because FYM did not reduce partial pressure of ammonia (pNH₃) following urea application in either season. Basal and delayed applications of urea were equally effective in the absence of FYM, but when FYM was applied rice yields in both seasons were higher for delayed (mean = 3.2 Mg ha^–1) than basal (mean = 2.9 Mg ha^–1) application of urea. Results suggest that recommendations for urea timing in irrigated lowland rice should consider whether farmers apply FYM.     

Fertilizer requirement of rice-wheat and maize-wheat rotations on coarse-textured soils amended with farmyard manure

Field experiments with rice-wheat rotation were conducted during five consecutive years on a coarse-textured low organic matter soil. By amending the soil with 12t FYM ha^–1, the yield of wetland rice in the absence of fertilizers was increased by 32 per cent. Application of 80 kg N ha^–1 as urea could increase the grain yield of rice equivalent to 120 kg N ha^–1 on the unamended soil. Although the soil under test was low in Olsen's P, rice did not respond to the application of phosphorus on both amended and unamended soils. For producing equivalent grain yield, fertilizer requirement of maize grown on soils amended with 6 and 12 t FYM ha^–1 could be reduced, respectively to 50 and 25 per cent of the dose recommended for unamended soil (120 kg N + 26.2 kg P + 25 kg K ha^–1). Grain yield of wheat grown after rice on soils amended with FYM was significantly higher than that obtained on unamended soil. In contrast, grain yield of wheat which followed maize did not differ significantly on amended or unamended soils.     

Benefits of organic residues and chemical fertilizer to productivity of rain-fed lowland rice and to soil nutrient balances

Low yields and high risk characterize many rain-fed lowland rice environments, including those in Laos. Drought and fluctuating soil-water conditions (from aerobic to anaerobic states) can limit productivity and the efficient use of applied nutrients. Although addition of organic matter may improve the efficiency of fertilizer use, on-farm residues, for example farmyard manure (FYM), rice straw and rice hulls, are, currently, poorly utilized in these systems. Single and multi-year experiments were designed to evaluate the effect of these residues on rice productivity and efficiency of fertilizer use at four sites. Rice yield without fertilizer but with addition of residues ranged from 1.1 to 1.7 t ha⁻¹ across sites and years. In response to fertilizer, yields increased on average by 1.4 t ha⁻¹. For all sites and years there was a significant response of yield to organic residues applied without fertilizer, with responses ranging from 0.2 to 1.4 t ha⁻¹. In 58% of cases there was no residue×fertilizer interaction (benefits of residues when applied with fertilizer were additive). In 38 and 4% of cases the interaction was negative (no response to residues if fertilizer was already applied) or positive (synergistic), respectively. In the multi-year studies, the type of interaction varied between years, suggesting that seasonal events, rather than soil type, determine the type of interaction. The greatest benefits of applying organic and chemical fertilizers together were observed in years when soil-water conditions were unfavorable (fluctuating anaerobic–aerobic conditions). The long-term effects of these different management strategies on soil nutrient balances suggest that N, P, and K balances were maintained as a result of balanced commercial fertilizer management but that addition of residues further enhanced these balances. All residues, when applied alone, resulted in positive soil Si balances; only with FYM were long-term N, P, and K balances maintained or positive, however. For resource-poor farmers, applying on-farm residues can be a sustainable approach to increasing productivity.     

Urea-rubber matrices as slow-release fertilizers

The efficacy of a prototype slow-release fertilizer, urea-rubber matrix (URM) was assessed under flooded rice conditions. URM cuboids of size 0.5 × 1.0 × 0.4 cm were applied in comparison with prilled urea at levels of 50, 130 and 200 kg N ha^?1. URM was placed at the soil/solution interface in intimate association with rice seedlings whereas prilled urea was broadcast into the floodwater to simulate the normal application method of South East Asian farmers. URM cuboid sizes of 0.25 × 0.5 × 0.4 cm, 0.5 × 0.5 × 0.4 cm and 1.0 × 1.0 × 0.4 cm were similarly evaluated at a single rate of 130 kg N ha^?1; a broadcast URM treatment was also included. Different methods of prilled urea application including deep placement and split application were also studied at a single rate of 130 kg N ha^?1. It was found that the build-up of floodwater N (urea + NH ₄ ⁺ ) from URM during the 13 days following application was almost negligible irrespective of level or method of application. This was thought to result in low losses of N through ammonia volatilization as shown by higher rice grain yields in comparison with prilled urea at all levels of application. Deep-placed urea gave a comparable grain yield to that of broadcast URM. There was no significant difference in grain yield between URM applied by placement and by broadcast, suggesting that URM can be effectively applied either in intimate association with rice seedlings or by broadcasting to the rice field before, or after, planting. An attempt to predict the release of urea from URM was made using a diffusion-based simulation model. It was found that the model underestimated the actual release of urea from URM within the rhizosphere, probably due to the extensive penetration by rice roots of the URM cuboids.     

Yield and growth response to potassium of grain sorghum as influenced by variety in a savanna soil of Nigeria

Field trials were conducted at Samaru over a three-year period (1980–82) to study the yield, growth and nutrient concentration of three grain sorghum varieties (L. 187, SK5912 and FFBL) in relation to potassium fertilization in a savanna soil. Potassium application rates were 0, 25, 50 and 75 kg K ha^–1. Year × potassium interactions were not significant although there were significant variety × K interactions. The highest grain yields for var. L.187, SK5912 and FFBL occurred from the application of 25, 50 and 75 kg K ha^–1 respectively. Straw yield was generally increased by K application, which also promoted tillering and hastened flowering in grain sorghum. Although grain weight per head, head number per m², grain number and 1000-grain weight were unaffected by this nutrient, weight per head was reduced by 22.8 per cent. K application enhanced N concentration of sorghum plants but caused decline in P concentration. The highest K rate gave the highest K concentration in each of the three varieties at 7 weeks after planting. Optimum K requirement of grain sorghum would seem to be between 25 and 50 kg K ha^–1.