No abstract

Cowpea [Vigna unguiculata (L.) Walp.] cultivars with high yield potential and suitable plant architecture for mechanized harvesting have recently shown a growing interest to be cultivated as a second crop in fall–winter season of southeastern Brazil. The agronomic optimal plant density (AOPD) is one of the main management factors defining attainable yield. However, in the scientific literature for semiupright cowpea cultivars grown in fall–winter season in southeastern Brazil the AOPD is not yet clearly defined. A 3‐yr study was conducted to evaluate the effect of five plant densities (100,000–500,000 plants ha−1) on growth, seed yield and its components for two cowpea cultivars (BRS Guariba and BRS Novaera) in Botucatu, southeastern Brazil. The AOPD for cowpea increased as the attainable yield improved. The increase in plant density promoted increases in leaf area index (LAI) and the position (measured in height) of the first pod insertion for cowpea plants, but negatively affected per‐plant scale surviving rate, leaf area, aboveground dry matter (DM), and yield resulting from intraspecific competition. Maximum cowpea seed yields were achieved with AOPD ranging from 216,630 to 290,537 plants ha−1 (8–24% greater than under the lowest plant density). On average, 259,000 plants ha−1 was estimated for the AOPD to achieve maximum seed yield of semiupright cowpea grown as a second crop in fall–winter season in southeastern Brazil.

The objective of this work was to evaluate the efficiency of molten and ground alkaline potassium-silicate rocks (K1) and of ground phonolite rock (K2) as sources of potassium for upland rice (Oryza sativa) and common bean (Phaseolus vulgaris) crops, in comparison with the traditional source (KCl). Two experiments - one with each crop - were conducted on a Typic Haplorthox in a randomized complete block design with four replicates. The treatments consisted of three sources (KCl, K1, and K2) and four rates (0, 20, 40, and 80 kg ha-1 K2O) of K. Regardless of the used source, K fertilization increased the leaf K content and grain yield of the upland rice and common bean crops. The agronomic efficiency index (AEI) of the alternative K sources varied according to the crop. For upland rice, the AEI of K2 was 8% higher than that of KCl at the recommended K rate, but similar at the highest rate. For common bean, the AEI values of K1 were close to that of KCl at the rates of 40 and 80 kg ha-1 K2O. The alternative sources K1 and K2 supply K and increase the grain yield of common bean and upland rice, respectively, similarly to KCl.

The objective of this work was to evaluate the agronomic and economic efficiency of phonolite rock (K2) and alkaline potassium-silicate rock (K3), ground and applied by surface broadcasting, as K sources for the soybean (Glycine max), corn (Zea mays), common bean (Phaseolus vulgaris), and upland rice (Oryza sativa) crops. Four experiments – one with each crop – were conducted in two crop years in a Typic Haplorthox in a randomized complete block design with four replicates. The treatments consisted of three sources (the KCl standard source, K2, and K3) and four rates (0, 0.5, 1.0, and 2.0 times the recommended for each crop) of K. The three sources increased similarly the leaf K concentration of soybean, corn, and common bean but had no effect on that of upland rice. The grain yield of all crops increased with the application of K2 and K3, as observed for KCl. The efficiency of the alternative K sources varies depending on the rate and crop. The K3 source is viable to be applied by broadcasting at the recommended K rate for all studied crops, while K2 is suitable only for soybean, corn, and common bean.

This study checked the nitrogen (N) uptake, fate of the N fertilizer, fertilizer recovery efficiency (FRE) and the residual amount of N fertilizer in the soil via 15 N-labelled fertilizer applied to soybean (Glycine max L. Merr.), to explain any differences in the yields. Two soybean field experiments were established in Brazil, one conducted in a tropical (Trop) zone located at Cerrado Biome and the other in a subtropical (Subt) environment. The experimental design was a 2-factor in randomized complete block with four replications. Five doses of N (0, 20, 40, 80 and 120 kg ha −1) were applied at two soybean growth stages (VE and R3). For all treatments, except No-N, 15 N-labelled fertilizer was used. The N uptake and the amount of N fertilizer were analysed in the roots, shoots, grains and whole plant, the FRE and yield by soybean, and the residual of fertilizer in the soil. The total N uptake (Nplant) was greater with fertilization at R3 stage compared to the other stage, and N application increased the yield just at this stage and in the Trop condition. The increase in N shoot (not specifically from fertilizer) with the application at R3 appeared to be related to the increased in yield. However, the N from fertilizer found in the plant shoot was about 20% higher when fertilizer was applied at VE compared with R3. Under Subt condition, the FRE averaging 55%. In contrast, the FRE decreased from low to high nitrogen rates (64 to 40%, respectively) when soybean grown under Trop condition. Most N from fertilizer (38%) was found in the grains, followed by the shoot (14.6%) and the root (0.58%). The use of N fertilizer at reproductive growth stages is a better approach to meet soybean N demand through N fertilization. Potential yield gains are more reliable under Trop condition.

The objective of this work was to evaluate the efficiency and the residual effects of both molten and ground alkaline potassium-silicate rocks (K1) and of ground phonolite rock (K2), as sources of potassium, compared with the traditional source (KCl), in grain crop successions. Two experiments – one with the succession soybean-wheat-corn and the other with the succession corn-millet-soybean – were conducted on a Typic Haplorthox in a randomized complete block design with four replicates. The treatments consisted of three sources (KCl, K1, and K2) and four rates of K (corresponding to 0, 0.5, 1.0, and 2.0 times the recommended rates for soybean and corn). The used sources did not affect leaf K concentration in soybean, but KCl and K2 similarly increased leaf K concentration in corn. Regardless of the source, K application increased the yield of all crops. The K1 and K2 sources present agronomic efficiencies equivalent to that of KCl. K1 and K2 show a more pronounced residual effect than KCl, especially on crops grown approximately one year after their application and under K rates above those recommended for the crops.

Interest in fall–winter species options for rotation with soybean (Glycine max (L.) Merr.) has arisen; however, little is known about how they can affect the performance of subsequent soybean under a no-tillage system in tropical environments. Our objective was to evaluate the leaf nutrient concentration, aboveground dry matter (DM) accumulation, macronutrient uptake, yield components, and seed yield of soybean cropped in succession to different crop species. Consequently, a field experiment was conducted during three consecutive growing seasons in Botucatu, São Paulo State, southeastern Brazil. The experiment was arranged in a randomized complete block design with four replicates. The treatments consisted of the cultivation of five crops (crambe (Crambe abyssinica Hochst. ex. R.E. Fries), maize (Zea mays L.), safflower (Carthamus tinctorius L.), sorghum (Sorghum bicolor (L.) Moench), and sunflower (Helianthus annuus L.)) in rotation with soybean, in addition to plots that lie fallow (spontaneous weeds) in the soybean off-season, totaling six treatments. Letting plots lie fallow during the off-season reduced the DM accumulation, nutrient uptake, and seed yield of the soybean crop in succession. Preceding cultivation of fall–winter crambe or sunflower favored the uptake of P, K, Ca, Mg, and S by the following soybean crop. The cultivation of sorghum, safflower, and crambe as fall–winter crops also increased the seed yield of subsequent soybean (from 12 to 18% on the average of three growing seasons) compared to fallow plots. The highest increases in soybean seed yield were found in succession to maize (37%) or sunflower (45%) in the second and third growing seasons, respectively.

The high seed yield and optimum harvesting of short-height castor (Ricinus communis L.) genotypes have enabled its large-scale cultivation and introduction in the Brazilian cropping systems. Thus, studies to optimize plant density are essential to adequate plant population since this is the key management to influence castor biomass and seed production. This study aimed to evaluate the influence of plant density by altering plant arrangement (i.e., spacing between and within rows) on growth, biomass production and partitioning, and seed yield of a castor cultivar in fall-winter cropping season. Field experiments were conducted over two seasons in southeastern Brazil. Two close-spaced (0.45 × 0.23 m and 0.45 × 0.44 m) and a traditional (0.90 × 0.44 m) plant arrangements were tested. Plant arrangements influenced plant growth, biomass production and partitioning, and seed yield. Compared to the traditional layout, close-spaced plant arrangements resulted in thinner basal stems and lower leaf area per plant, but increased leaf area index. The plant arrangement with higher plant density increased per-unit area production of stem plus leaf biomass (43-48%), which also resulted in increased (24%) seed yield, compared to traditional layout. Although a greater amount of biomass was partitioned to reproductive organs in close-spaced plant arrangements, this allocation was not enough to influence the harvest index. Therefore, the adaptive performance of short-height castor adjusting biomass partitioning to maximize stem plus leaf biomass production and seed yield at close-spaced plant arrangement demonstrated this to be a suitable option to cultivate in the Brazilian fall-winter season.