YIELD AND YIELD COMPONENTS OF UPLAND RICE AS INFLUENCED BY NITROGEN SOURCES

Ammonium sulfate and urea are main sources of nitrogen (N) for annual crop production in developing countries. Two greenhouse experiments were conducted using ammonium sulfate and urea as N sources for upland rice grown on a Brazilian Oxisol. The N rates used were 0, 50, 100, 150, 3000, and 400 kg N kg^?1 of soil. Yield and yield components were significantly increased in a quadratic fashion with increasing N rate. Ammonium sulfate X urea interaction was significant for grain yield, shoot dry matter yield, panicle number, plant height and root dry weight, indicating a different response magnitude of these plant parameters to two sources of N. Based on regression equation, maximum grain yield was achieved with the application of 380 mg N kg^?1 by ammonium sulfate and 271 mg N kg^?1 by urea. Grain yield and yield components were reduced at higher rates of urea (>300 mg kg N) but these plant parameters’ responses to ammonium sulfate at higher rates was constant. In the intermediate N rate range (125 to 275 mg kg^?1), urea was slightly better compared to ammonium sulfate for grain yield. Grain yield was significantly related with plant height, shoot dry weight, panicle number, grain harvest index and root dry weight. Hence, improving these plant characteristics by using appropriate soil and plant management practices can improve upland rice yield.     

UPLAND RICE GENOTYPES EVALUATION FOR PHOSPHORUS USE EFFICIENCY

Phosphorus (P) deficiency is one of the most yield limiting factors in crop production in Brazilian Oxisols. A greenhouse experiment was conducted to evaluate 20 upland rice genotypes at low (25 mg P kg^?1) and high (200 mg P kg^?1) P levels applied to a Brazilian Oxisol. Grain yield and yield components were significantly influenced by P level and genotype treatments. There was a significant interaction between P level and genotype treatments in relation to grain yield, indicating genotypes responded differently under two P levels. Based on grain yield efficiency index (GYEI), genotypes were classified into efficient, moderately efficient and inefficient groups. The efficient genotypes in utilizing P were ‘BRA052053’, ‘BRS Primavera’, ‘BRA052015’, ‘BRA052023’, ‘BRA01506’, ‘BRA052045’, ‘BRA032033’, ‘BRA01596’ and ‘BRA052034’. Remaining genotypes were classified as moderately efficient in P use efficiency. None of the genotypes were fall into inefficient group. Grain yield was significantly and positively related with shoot dry weight, panicle number, grain harvest index, 1000-grain weight and had a negative and significant correlation with spikelet sterility. Grain weight was having maximum contribution in total rice plant weight comparing to root and shoot, indicating improvement in harvest index of modern Brazilian upland rice cultivars by breeding.     

Comparative Efficiency of Phosphorus Sources for Upland Rice Production

Rice (Oryza sativa L.) is a staple food for more than 50% of the world’s population, and phosphorus (P) is one of the most yield-limiting nutrients for rice production in tropical acidic soils worldwide. A greenhouse experiment was conducted to evaluate efficiency of six P sources for upland rice production. The P sources used were simple superphosphate (SSP), polymer-coated SSP (PSSP), triple superphosphate (TSP), polymer-coated TSP (PTSP), monoammonium phosphate (MAP), and polymer-coated MAP (PMAP). There were four P rates [50, 100 200, and 400 mg phosphorus (P) kg^?1] applied with four sources plus one control treatment [0 mg phosphorus (P) kg^?1]. Plant height, straw yield, grain yield, panicle density, root dry weight, maximum root length, and 1000-grain weight were significantly increased with increasing P rates in the range of 0 to 400 mg P kg^?1. However, P-use efficiency (mg grain produced per mg P applied) was decreased with increasing P rate. Based on regression equation, overall maximum plant height was obtained with the application of 235 mg P kg^?1, maximum straw yield with the application of 265 mg P kg^?1, and maximum grain yield at 227 mg P kg^?1. Based on maximum grain yield, the P source were classified as PMAP > SSP = MAP > PSSP > TSP > PTSP in the upland rice production efficiency. Overall, maximum panicle density was obtained with the addition of 231 mg P kg^?1 and maximum 1000-weight was obtained with the addition of 226 mg P kg^?1. Similarly, overall root dry weight and maximum root length were achieved with the application of 261 and 298 mg P kg^?1 of soil. Most of the growth and yield components had a significant positive association with grain yield. Optimum soil acidity indices such as pH; exchangeable calcium (Ca), magnesium (Mg), and potassium (K); Ca, Mg, and K saturation; base saturation; and acidity saturation were established for maximum upland rice grain yield.     

Phosphorus Nutrition of Upland Rice,Dry Bean,Soybean, and Corn Grown on an Oxisol

Rice, dry bean, corn, and soybean are important food crops. Phosphorus (P) deficiency is one of the most yield-limiting factors for these crops grown on highly weathered Brazilian Oxisols. Four greenhouse experiments were conducted to determine P requirements of these four crops. The P levels used were 0, 50, 100, 200, and 400 mg kg^?1. Growth, yield, and yield components evaluated of four crop species were significantly increased with the application of P fertilization. Most of the responses were quadratic in fashion when the P was applied in the range of 0 to 400 mg kg^?1. Maximum grain yield of upland rice was obtained with the application of 238 mg P kg^?1 of soil, maximum dry bean grain yield was obtained with the application of 227 mg P kg^?1 of soil, and maximum grain yield of soybean was obtained with the application of 224 mg P kg^?1 of soil. Maximum shoot growth of corn was obtained with the addition of 323 mg P kg^?1 of soil. Most of the growth and yield components had significant positive association with grain yield or shoot dry weight. Phosphorus concentration and uptake were greater in the grain compared to straw in upland rice and dry bean plants. Overall, P-use efficiencies decreased with increasing P rates.     

Potassium-Use Efficiency in Upland Rice Genotypes

Potassium (K) uptake is greatest among essential nutrients for rice. Data related to yield, yield components, and K-use efficiency by upland rice genotypes are limited. A greenhouse experiment was conducted to evaluate influence of K on growth, yield and yield components, and K-use efficiency by upland rice genotypes. Potassium levels applied to an Oxisol were zero (natural K level) and 200 mg K kg¹ of soil and 20 upland rice genotypes were evaluated. Plant height, shoot dry weight, grain yield, 1000-grain weight, and spikelet sterility were significantly affected by K and genotype treatments. Genotypes Primavera and BRA 1600 were the most efficient and genotype BRAMG Curinga was most inefficient in producing grain yield. Plant growth (plant height and shoot dry weight) and yield components (panicle number, grain harvest index, 1000-grain weight, and panicle length) were significantly and positively associated with grain yield. However, spikelet sterility was significantly and negatively correlated with grain yield.     

Phosphorus Nutrition of Lowland Rice in Tropical Lowland Soil

Rice is a main food crop for about half of the world's population, and phosphorus (P) is the main limiting nutrient in rice production in tropical lowlands. A greenhouse experiment was conducted to evaluate P requirements of lowland rice grown on a lowland soil (Inceptisol). Dry matter, grain yield, and yield-attributing characteristics were significantly (P < 0.01) influenced by P fertilization. Based on quadratic response, maximum shoot dry weight and grain yield were obtained with the application of 190 mg P kg^?1 of soil. Maximum panicle, tiller number, and plant height were obtained with the application of 177 192, and 175 mg P kg^?1 of soil, respectively. Mehlich 1–extractable P for maximum grain yield was 15.6 mg kg^?1 of soil. Variability in grain yield with plant growth and yield parameters was in the order of tiller > shoot dry weight > panicle number > spikelet sterility > plant height > grain harvest index > panicle length > weight of 1000 grains. Phosphorus uptake in shoot and concentration and uptake in grain significantly (P < 0.01) increased grain yield. However, variability in grain yield was greater with concentration and uptake of P in the grain. Similarly, P harvest index was also significantly associated with grain yield. Agronomic P-use efficiency, apparent P-recovery efficiency, and P-utilization efficiency decreased quadratically with increasing P rates, whereas physiological P-use efficiency increased quadratically and agrophysiological P-use efficiency decreased linearly with increasing P rates. Agrophysiological and utilization P-use efficiencies had significant positive correlation with grain yield.     

Phosphorus Use Efficiency in Upland Rice Genotypes Under Field Conditions

Phosphorus (P) deficiency is one of the most yield limiting factors for crop production in South American soils. Upland rice (Oryza sativa L.) is an important crop in South American cropping systems, including Brazil. A field experiment was conducted with the objective to evaluate 20 upland rice genotypes for phosphorus (P) use efficiency. The P rate used was low (0 kg P ha^?1) and high [87 kg P ha^?1 or 200 kg phosphorus pentoxide (P₂O₅) ha^?1]. Plant height, shoot dry weight, grain yield, panicle number, 1000 grain weight, spikelet sterility, and grain harvest index were significantly influenced by P and genotype treatments. The P X genotype interaction was significant for grain yield, indicating that genotypes responded differently under two P rates. Overall, grain yield increased by 12% with the addition of P fertilization. Based on grain yield efficiency index, genotypes were classified into efficient, moderately efficient, and inefficient group. The genotypes that were classified as efficient in P use were BRA032048, BRA042094, BRA02601, BRA032051, BRA032033, BRA052015, BRA042156, BRA01600, BRA01506, BRA052023 and BRA042160. The inefficient genotypes in P us efficiency were BRS Primavera, BRA052045, BRA01596, and BRS Sertaneja. Grain harvest index had a significant positive association with grain yield and spikelet sterility had a significant negative association with grain yield, as expected. Average, P-use efficiency of five genotypes was about 17 kg kg^?1 (kg grain yield per kg P applied).     

Yield and Yield Components and Phosphorus Use Efficiency of Lowland Rice Genotypes

Phosphorus deficiency is main constraints for lowland rice production in various rice producing regions of the world. A greenhouse experiment was conducted using lowland (Inceptisol) soil with the objective to determine response of seven lowland rice (Oryza sativa L.) genotypes to phosphorus fertilization and to evaluate their phosphorus (P) use efficiency. Phosphorus treatments included control (0 mg P kg^?1) and 200 mg P kg^?1 of soil. Plant height and shoot dry weight were significantly (P < 0.001) influenced by P treatments. Phosphorus X genotypes interaction was significant for shoot dry weight, indicating different response of genotypes under two P levels. At low P level, none of the genotypes produced grain yield, indicating original P level in the soil was too low for lowland rice yield. However, genotypes differed significantly in grain yield at high P level. Panicle number, panicle length, and thousand grains weight had a significant quadratic association with grain yield. However, spikelet sterility had a significant linear negative association with grain yield. The P use efficiency expressed as agronomic efficiency (AE), physiological efficiency (PE), agro-physiological efficiency (AP), apparent recovery efficiency (ARE), and utilization (UE) were significantly different among genotypes. These efficiencies were having significantly positive association with grain yield, with exception to ARE, indicating improving grain yield with improved P use efficiencies in rice.     

Phosphorus Uptake by Upland Rice From Superphosphate Fertilizers Produced With Sulfuric Acid Treatments of Brazilian Phosphate Rocks

Upland rice is an important crop in Brazilian agriculture and phosphorus (P) deficiency is one of the most yield limiting factors for this crop. A greenhouse experiment was carried out with the objective of evaluating response of upland rice to P rate and sources. The treatment consisted five P rates: 0, 25, 50, 100, and 200 mg dm^?3 supplied through four P sources: Araxa, Catalão, Irece, and Lagamar. The soil used in the experiment was a Typic Hapludox. Rice grain yield, shoot dry weight, and root dry weight was significantly increased with increasing resin extractable P in the soil. Maximum shoot dry weight and grain yield was achieved with resin extractable P of 30 mg P dm^?3. However, root dry weight increased linearly with increasing P concentration in the range of 4 to 72 mg dm^?3. Shoot dry weight, grain yield, and root dry weight increased significantly in a quadratic fashion with increasing P concentration in the shoot. Rice yield and P uptake were not affected significantly with P sources. Grain Cd concentration also was significantly affected by P rates but did not exceed the permissible concentration for human consumption, according to Brazilian food legislation.     

NITROGEN USE EFFICIENCY IN UPLAND RICE GENOTYPES

Nitrogen (N) deficiency is one of the most yield-limiting nutrients in upland rice growing regions word wide. A greenhouse experiment was conducted with the objective to evaluate nineteen upland rice (Oryza sativa. L.) genotypes for N use efficiency. The soil used in the experiment was an Oxisol and two N levels used were without N application (low level) and an application of 400 mg N kg^?1 of soil (high level). Grain yield and yield components and N uptake parameters were significantly affected by N and genotype treatments. Regression analysis showed that plant height, shoot dry weight, number of panicles per pot, number of grains per panicle, grain harvest index, N uptake in shoot and grain were having significant positive relation with grain yield. Nitrogen concentration of 6.4 g kg^?1 in the shoot is established as deficient level and 9.5 g kg^?1 as sufficient level at harvest. Agronomic efficiency of N (grain yield/unit of N applied) and N utilization efficiency (physiological efficiency X apparent recovery efficiency) were significantly different among genotypes. These two N use efficiencies were having significant quadratic relationship with grain yield. Soil pH, exchangeable soil Ca and base saturation were having significantly positive association with grain yield. However, soil extractable phosphorus (P), potassium (K), hydrogen (H⁺), aluminum (Al) and cation exchange capacity were having significantly negative association with grain yield.     

Lowland Rice Genotypes Evaluation for Nitrogen Use Efficiency

Rice is important crop for world population, including Brazil. Nitrogen (N) is one of the most yield limiting nutrients in rice production under all agro-ecological conditions. A greenhouse experiment was conducted to evaluate N responses to 12 lowland rice genotypes. Soil used in the experiment was a Gley humic according to Brazilian soil classification system and Inceptisol according to USA soil taxonomy classification. The N rates used were 0 mg kg^?1 (low) and 300 mg kg^?1 (high) of soil. Plant height, straw yield, grain yield, panicle density, 1000 grain weight, and root dry weight were significantly increased with the addition of N fertilization. These growth, yield, and yield components were also significantly influenced by genotype treatment. Grain yield had significant linear or quadratic association with shoot dry weight, panicle number and 1000 grain weight Based on grain efficiency index genotypes were classified as efficient, moderately efficient and inefficient in N use. The N efficient genotypes were ‘BRS Tropical’, ‘BRS Jaçanã’, ‘BRA 02654’, ‘BRA 051077’, ‘BRA 051083’, ‘BRA 051108’, ‘BRA 051130’ and ‘BRA 051250’. Remaining genotypes fall into moderately efficient group. None of the genotypes were grouped as inefficient in N use efficiency.     

Screening Upland Rice Genotypes for Manganese‐use Efficiency

Manganese (Mn) deficiency in upland rice grown after common bean or soybean, which received adequate rate of liming on highly weathered Oxisols, is observed. A greenhouse experiment was conducted to evaluate Mn‐use efficiency of 10 promising upland rice genotypes. The genotypes were grown on an Oxisol at 0 mg Mn kg^?1 (natural soil Mn level) and 20 mg Mn kg^?1 of soil applied as manganese sulfate. Grain yield, panicle number, and grain harvest index (GHI) were significantly (P < 0.01) influenced by genotype. However, shoot dry weight was significantly affected by Mn as well as genotype treatments. Manganese uptake in the shoot as well as in the grain was also affected by genotype treatment. On the basis of Mn‐use efficiency (mg grain weight/mg Mn accumulated in shoot and grain), genotypes were classified as efficient and responsive (ER), efficient and nonresponsive (ENR), nonefficient and responsive (NER), and nonefficient and nonresponsive (NENR). Genotypes Carisma, CNA8540, and IR42 were classified as ER, and genotypes CNA8557 and Maravilha were classified as ENR. Genotype Caipo was in the group NER, and in the NENR group were genotypes Bonança, Canastra, Caraja, and Guarani. From a practical point of view, genotypes that produce high grain yield at a low level of Mn and respond well to Mn additions are the most desirable because they are able to express their high yield potential in a wide range of Mn availability.     

Agronomic Evaluation of Phosphorus Sources in Lowland Rice Production

Phosphorus (P) deficiency is one of the most yield-limiting factors in lowland rice production on Brazilian Inceptisol. The objective of this study was to evaluate eight P sources for lowland rice production. The P sources were simple superphosphate (SSP), polymer-coated simple superphosphate (PSSP), ammoniated simple superphosphate (ASSP), polymer-coated ammoniated simple superphosphate (PASSP), triple superphosphate (TSP), polymer-coated triple superphosphate (PTSP), monoammonium phosphate (MAP), and polymer-coated monoammonium phosphate (PMAP). These P sources were applied in four rates (i.e., 50, 100 200, and 400 mg P kg^?1) + one control treatment (0 mg P kg^?1). Plant height, straw yield, grain yield, panicle number, and root dry weight were significantly increased in a quadratic fashion with increasing P levels from 0 to 400 mg kg^?1 of all the P sources evaluated. However, overall maximum root length and P-use efficiency were significantly less at greater P levels. Based on regression equation, maximum plant height was obtained with 262 mg P kg, maximum straw yield was obtained with 263 mg P kg^?1, maximum grain yield was obtained with 273 mg P kg^?1, and maximum panicle density was obtained with 273 mg P kg^?1. Plant growth and yield components had significant positive association with grain yield, except maximum root length. Based on grain yield and average P rate of maximum grain yield, which is 273 mg kg^?1, P sources were classified for P-use efficiency in the order of PSSP = TSP > PTSP > PASSP > SSP > MAP > ASSP. Soil chemical properties [pH; P; potassium (K); calcium (Ca); magnesium (Mg); hydrogen (H) + aluminum (Al); cation exchange capacity (CEC); base saturation; Ca, Mg, and K saturation; acidity saturation; Ca/Mg, Ca/K, and Mg/K ratios] changed significantly with the addition of different P treatments.     

Potassium Requirements of Lowland Rice

Rice is a staple food for about 50 percent of the world’s population. Potassium (K) is absorbed in large amounts by rice plants and adequate amounts of this element are fundamental to improve productivity and maintain sustainability of the cropping systems. A greenhouse experiment was conducted to determine the adequate rate of K for lowland rice grown on a Brazilian Inceptisol. The K rates used were 0, 50, 100, 200, 400, and 600 mg K kg^?1 soil. Most of the growth, yield, and yield components were significantly and quadratically increased with increasing K levels. Based on a quadratic equation, maximum grain yield was obtained with the addition of 371 mg K kg^?1 soil. Maximum plant height and shoot dry weight were obtained at 414 and 398 mg K kg^?1 soil, respectively. Root growth (maximum length and dry weight) was also significantly increased in a quadratic fashion with the increasing K rate in the growth medium. Maximum root length was achieved at 58 mg K kg^?1 whereas maximum root dry weight was obtained with the addition of 394 mg K kg^?1 soil. Plant height, shoot dry weight, 1000-grain weight, root length, and root dry weight were significantly associated with grain yield. Hence, manipulation of these growth and yield components with the addition of K fertilizer can improve yield of lowland rice in varzea soils of central part of Brazil. Potassium uptake increased significantly in a quadratic fashion with increasing K rate. However, K-use efficiency (mg grain per mg K applied) decreased significantly with increasing K rate in a quadratic fashion. Maximum grain yield was obtained with 117 mg kg^?1 Mehlich 1–extractable K, base saturation of 53 percent, Mg saturation of 9 percent, K saturation of 2 percent, and Ca/Mg ratio of 4.     

Zinc-Use Efficiency in Upland Rice Genotypes

Zinc (Zn) deficiency is very common in annual crops grown on Brazilian Oxisols. A greenhouse experiment was conducted to evaluate Zn-use efficiency of 20 upland rice genotypes. The Zn levels used were 0 mg kg^?1 (natural level of the soil) and 20 mg kg^?1 of soil applied with zinc sulfate (ZnSO₄). Zinc × genotype interactions were significant for grain yield, panicle number, panicle length, root dry weight, and specific root length, indicating different responses of genotypes with the variation of Zn levels and that selection for Zn-use efficiency is necessary at low as well as at high Zn rates. Based on Zn-use efficiency index, 11 genotypes were classified as efficient and nine were classified as moderately efficient. The most Zn-efficient genotypes were BRA 01596, BRA 042156, BRA 052053, BRA Primavera, and BRA 01506. The most inefficient genotypes in Zn-use efficiency were BRA 042094, BRA 052045, BRA 052034, and BRA 052023. Grain yield and most of the yield attributing characteristics have significant Zn × genotype interactions, which indicate that genotypes respond differently under different Zn levels. Thus, genotype selection is an important strategy for upland rice production in Brazilian Oxisols.     

Influence of Lime and Gypsum on Growth and Yield of Upland Rice and Changes in Soil Chemical Properties

Upland rice is an important crop in the cropping systems of South America, including Brazil. Two greenhouse experiments were conducted to determine influence of lime and gypsum on yield and yield components of upland rice and changes in the chemical properties of an Oxisol. The lime rates used were 0, 0.71, 1.42, 2.14, 2.85, and 4.28 g kg^?1 soil. The gypsum rates were 0, 0.28, 0.57, 1.14, 1.71, and 2.28 g kg^?1. Lime as well as gypsum significantly increased plant height, straw and grain yield, and panicle density in a quadratic fashion. Adequate lime and gypsum rates for maximum grain yield were 1.11 g kg^?1 and 1.13 g kg^?1, respectively. Plant height, straw yield, and panicle density were positively related to grain yield. Lime as well as gypsum application significantly changed extractable calcium (Ca), magnesium (Mg), hydrogen (H)+aluminum (Al), base saturation, and effective cation exchange capacity. In addition, liming also significantly increased pH, extractable phosphorus (P) and potassium (K), calcium saturation, magnesium saturation, and potassium saturation. Optimum acidity indices for the grain yield of upland rice were pH 6.0, Ca 1.7 cmol_c kg^?1, base saturation 60%, and calcium saturation 47%. In addition, upland rice can tolerate 42% of acidity saturation.     

秸秆覆盖与氮肥运筹对杂交稻根系生长及氮素利用的影响

【目的】在我国稻-麦、稻-油等多熟制区域,富含氮素的小麦、油菜等水稻前茬作物秸秆被大量弃置、焚烧,造成极大浪费和环境污染,与此同时,稻季氮肥投入量却在逐年增加,因此在水稻生产中研究秸秆覆盖与氮肥配合施用的理论与技术,对实现秸秆还田与减少氮肥用量具有重要意义。本试验研究油菜、小麦2种秸秆覆盖方式下,3种不同的氮肥运筹方式对杂交稻主要生育时期根系生长、氮素吸收利用特征及产量的影响,并探讨其根系生长与氮素利用及产量间的关系,以期寻求最佳的秸秆还田与氮肥运筹搭配模式。【方法】本试验以杂交稻F优498为材料,采用两因素裂区试验设计,主区为小麦秸秆覆盖(S1)、油菜秸秆覆盖(S2)和无秸秆覆盖(S0);副区为氮肥运筹模式,在135 kg/hm2总施氮量条件下,设置基肥∶蘖肥∶穗肥为5∶3∶2(N1);基肥∶蘖肥∶穗肥为3∶3∶4(N2);基肥∶蘖肥∶穗肥为3∶1∶6(N3)3种氮肥运筹模式,以不施氮肥(N0)为对照。研究各处理杂交稻在移栽后20 d、移栽后30 d、齐穗期和成熟期根系生长及形态、各生育期的干物质与氮素积累,水稻茎鞘的干物质转运、产量及其构成因子以及各时期氮素积累及利用效率,同时对各生育时期根系生长与氮素利用及产量间的关系进行分析。【结果】结果表明,小麦秸秆覆盖均可有效促进杂交稻各生育时期的根系生长、改善根系形态、增加各时期的干物质与氮素积累,提高氮肥的利用效率及稻米产量。在不同种类秸秆覆盖下,基肥∶蘖肥∶穗肥(倒4叶龄期施入)为3∶3∶4(N2)时,可及时地对杂交水稻主要生育时期的根系生长进行调控,有效促进抽穗至成熟期的干物质积累与转运率,提高水稻主要生育时期的氮素积累及氮肥利用效率,显著增加稻谷产量,为本试验中最优的氮肥管理模式;而氮肥后移比例过高(基肥∶分蘖肥∶穗肥运筹比例为3∶1∶6),会限制齐穗期根系的生长,导致稻谷产量及氮肥利用效率降低。相关性分析表明,秸秆覆盖与氮肥运筹下主要生育时期根干重、根体积、总根长与产量及氮素吸收利用均存在显著或极显著的正相关(r=0.38*0.78**),尤其以齐穗期的根体积与总根长、根干重与氮素累积、产量及氮素回收利用率的相关性最好。【结论】小麦秸秆、油菜秸秆覆盖能够有效促进杂交稻根系的生长,增加干物质与氮素积累,提高氮肥利用效率,且小麦秸秆覆盖效果更显著。秸秆覆盖条件下,氮肥运筹以基肥∶蘖肥∶穗肥为3∶3∶4时的水稻根系生长旺盛,物质生产能力强,氮肥利用效率最高。因此,小麦秸秆覆盖与基肥∶蘖肥∶穗肥以3∶3∶4的比例配合的水稻的产量最高,为最优组合。     

PHOSPHORUS UPTAKE AND USE EFFICIENCY IN FIELD CROPS

Phosphorus (P) is required by crop plants for many physiological and biochemical functions. Knowledge of phosphorus uptake and its use by crop plants is essential for adequate management of this essential nutrient. A field experiment was conducted during four consecutive years to determine P uptake and use efficiency by upland rice, dry bean, corn and soybean grown in rotation on a Brazilian Oxisol. Plant samples were taken at different growth stages during the growth cycle of each crop for phosphorus analysis. Phosphorus concentration (content per unit dry matter) significantly decreased in a quadratic fashion with the advancement of plant age in four crop species. Phosphorus concentration was higher in legumes compared to cereals. Phosphorus uptake in shoot, however, significantly increased in an exponential quadratic fashion with the advancement of plant age of crop species. At harvest, P uptake was higher in grain compared to shoot, indicating importance of this element in improving crop yields. Phosphorus use efficiency (grain or straw yield per unit P uptake) was higher in cereals compared to legumes. The P use efficiency for grain production was 465 kg kg^?1 for upland rice, 492 kg kg^?1 for corn, 229 kg kg^?1 for dry bean and 280 kg kg^?1 for soybean. The higher P use efficiency in cereals was associated with higher yield of cereals compared to legume species.     

Comparison of Conventional and Polymer Coated Urea as Nitrogen Sources for Lowland Rice Production

Nitrogen (N) is one of the most yield limiting nutrients in lowland rice production. Improving N use efficiency is essential to reduce cost of crop production and environmental pollution. A greenhouse experiment was conducted with the objective to compare conventional and polymer coated urea for lowland rice production. Grain yield, straw yield, panicle density, maximum root length, and root dry weight were significantly increased in a quadratic fashion with the increase of N rate from 0 to 400 mg kg^?1 soil. Nitrogen source X N rate interactions for most of these traits were not significant, indicating that lowland rice responded similarly to change in N rates of two N sources. Based on regression equations, maximum grain yield was obtained with the application of 258 mg N kg^?1 soil and maximum straw yield was obtained with the addition of 309 mg N kg^?1 soil. Nitrogen use efficiency (grain yield per unit of N applied) was maximum for polymer coated urea compared to conventional urea. Root length and root dry weight improved at an adequate N rate, indicating importance of N fertilization in the absorption of water and nutrients and consequently yield. Polymer coated urea had higher soil exchangeable calcium (Ca) and magnesium (Mg), Ca saturation, Mg saturation, base saturation, and effective cation exchange capacity compared to conventional urea. There was a highly significant decrease in soil exchangeable potassium (K) with increasing N rates at harvest of rice plants.     

Lowland Rice Genotypes Evaluation for Potassium-Use Efficiency

Lowland rice significantly contributes to world as well as Brazilian rice production and information on genotypes potassium-use efficiency is limited. A greenhouse experiment was conducted with the objective to evaluate lowland rice genotypes for potassium (K)–use efficiency. Ten genotypes were evaluated at 0 mg K kg^?1 (low) and 200 mg K kg^?1 (high) of soil. Grain yield and shoot dry weight were significantly affected by K as well as genotype treatments. Genotypes CNAi 8860, CNAi 8859, BRS Fronteira, and BRS Alvorada were the best in relation to K-use efficiency because they produced best grain yield at low as well as at higher K levels. Shoot dry weight, number of panicles per pot, and 1000-grain weight had highly significant (P < 0.01) association with grain yield. Spikelet sterility, however, had significant negative association with grain yield. These plant parameters were mainly influenced by genotypes, indicating importance of selecting appropriate genetic material for improving grain yield. Soil K depletion was significant at harvest, suggesting large amount of K uptake by lowland rice genotypes.