Insufficient nitrogen supply from symbiotic fixation reduces seasonal crop growth and nitrogen mobilization to seed in highly productive soybean crops

Nitrogen (N) supply can limit the yields of soybean [Glycine max (L.) Merr.] in highly productive environments. To explore the physiological mechanisms underlying this limitation, seasonal changes in N dynamics, aboveground dry matter (ADM) accumula- tion, leaf area index (LAI) and fraction of absorbed radiation (fAPAR) were compared in crops relying only on biological N2 fixation and available soil N (zero-N treatment) versus crops receiving N fertilizer (full-N treatment). Experiments were conducted in seven high-yield environments without water limitation, where crops received optimal management. In the zero-N treatment, biological N2 fixation was not sufficient to meet the N demand of the growing crop from early in the season up to beginning of seed filling. As a result, crop LAI, growth, N accumulation, radiation-use efficiency and fAPAR were consistently higher in the full-N than in the zero-N treatment, leading to improved seed set and yield. Similarly, plants in the full-N treatment had heavier seeds with higher N concentration because of greater N mobilization from vegetative organs to seeds. Future yield gains in high-yield soybean production systems will require an increase in biological N2 fixation, greater supply of N from soil or fertilizer, or allevia- tion of the trade-off between these two sources of N in order to meet the plant demand

Macro and Micro-Nutrient Accumulation and Partitioning in Soybean Affected by Water and Nitrogen Supply

This study aimed to investigate the influence of water availability and nitrogen fertilization on plant growth, nutrient dynamics, and variables related to soybean crop yield. Trials were performed in Teresina, Piauí, Brazil, using randomized blocks in a split-split plot arrangement. The plots corresponded to water regimes (full and deficient), the split plots to N fertilization (0 and 1000 kg ha-1 N-urea), and the split-split plots to harvest times of soybean plants (16, 23, 30, 37, 44, 58, 65, 79 and 86 days after emergence), with three replicates. In general, the accumulation and partitioning of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulphur (S), copper (Cu), iron (Fe), manganese (Mn), zinc (Zn) and boron (B) were decreased in plants subjected to water deficit and without N fertilization. Although nitrogen fertilization promoted elevated N accumulation in tissues, it did not result in any significant yield gain, and the highest seed yields were found in plants under full irrigation, regardless of N supplementation. However, deficient irrigation decreased the seed oil content of N-fertilized plants. In conclusion, N fertilization is critical for nutrient homeostasis, and water availability impairs biomass and nutrient accumulation, thereby limiting soybean yield performance

Understanding Nitrogen Limitation In Soybean

Meeting soybean demand on existing cropland area for a global population of 9.7 billion people by the year 2050 requires narrowing the existing gap between average producer yield and yield potential. Soybean relies on two sources on nitrogen (N): biological N2 fixation and indigenous soil N supply. As soybean yield continues to increase, it seems critical to know if there is a yield level at which potential contribution of indigenous nitrogen sources and fixation becomes insufficient to meet crop N requirements for high yields, while still maintaining or increasing protein and oil concentration. This study evaluated N limitation across 29 high-yield soybean environments in Argentina and Nebraska from 2015 to 2017. Each environment included a ‘zero-N’ treatment, which forced the crop to rely on biological N2 fixation and indigenous soil N, and a ‘full-N’ treatment, which provided an ample fertilizer N supply during the entire crop cycle based on novel protocol developed also in this study. Seed yield and protein concentration in full N were 11% and 3% higher than zero-N, respectively. The magnitude of the difference depended upon the yield level of the production environment, ranging from 0 kg ha-1 at 2.5 Mg ha-1 up to 900 kg ha-1 at 6 Mg ha-1. Seed yield responses were directly related with increases in accumulated N in aboveground biomass (70 kg N ha-1), without changes in nitrogen use efficiency. The N limitation was mitigated in environments with large contribution of indigenous soil N supply. The maximum rates of N limitation occurred before the seed filling and the plant mechanisms and processes underlying seed yield and protein concentrations were leaf area index, absorbed solar radiation, and N remobilization. Finally, there was a trade-off between biological N2 fixation and indigenous soil N supply with fixation reduced less than proportional per unit increase in indigenous N sources. There was a temporal asynchrony between biological N2 fixation and N demand, that is, biological N2 fixation was not sufficient to meet plant N demand as the latter increased and the contribution of indigenous soil N supply decreased. The peak of indigenous soil N supply was the most important factor explaining variation in the N limitation across environments. Findings from this study will help to narrow soybean yield gap to meet future food demand. Advisor: Patricio Grassin

Understanding Nitrogen Limitation in Soybean

Meeting soybean demand on existing cropland area for a global population of 9.7 billion people by the year 2050 requires narrowing the existing gap between average producer yield and yield potential. Soybean relies on two sources on nitrogen (N): biological N2 fixation and indigenous soil N supply. As soybean yield continues to increase, it seems critical to know if there is a yield level at which potential contribution of indigenous nitrogen sources and fixation becomes insufficient to meet crop N requirements for high yields, while still maintaining or increasing protein and oil concentration. This study evaluated N limitation across 29 high-yield soybean environments in Argentina and Nebraska from 2015 to 2017. Each environment included a ‘zero-N’ treatment, which forced the crop to rely on biological N2 fixation and indigenous soil N, and a ‘full-N’ treatment, which provided an ample fertilizer N supply during the entire crop cycle based on novel protocol developed also in this study. Seed yield and protein concentration in full N were 11% and 3% higher than zero-N, respectively. The magnitude of the difference depended upon the yield level of the production environment, ranging from 0 kg ha-1 at 2.5 Mg ha-1 up to 900 kg ha-1 at 6 Mg ha-1. Seed yield responses were directly related with increases in accumulated N in aboveground biomass (70 kg N ha-1), without changes in nitrogen use efficiency. The N limitation was mitigated in environments with large contribution of indigenous soil N supply. The maximum rates of N limitation occurred before the seed filling and the plant mechanisms and processes underlying seed yield and protein concentrations were leaf area index, absorbed solar radiation, and N remobilization. Finally, there was a trade-off between biological N2 fixation and indigenous soil N supply with fixation reduced less than proportional per unit increase in indigenous N sources. There was a temporal asynchrony between biological N2 fixation and N demand, that is, biological N2 fixation was not sufficient to meet plant N demand as the latter increased and the contribution of indigenous soil N supply decreased. The peak of indigenous soil N supply was the most important factor explaining variation in the N limitation across environments. Findings from this study will help to narrow soybean yield gap to meet future food demand

Understanding Nitrogen Limitation In Soybean

Meeting soybean demand on existing cropland area for a global population of 9.7 billion people by the year 2050 requires narrowing the existing gap between average producer yield and yield potential. Soybean relies on two sources on nitrogen (N): biological N2 fixation and indigenous soil N supply. As soybean yield continues to increase, it seems critical to know if there is a yield level at which potential contribution of indigenous nitrogen sources and fixation becomes insufficient to meet crop N requirements for high yields, while still maintaining or increasing protein and oil concentration. This study evaluated N limitation across 29 high-yield soybean environments in Argentina and Nebraska from 2015 to 2017. Each environment included a ‘zero-N’ treatment, which forced the crop to rely on biological N2 fixation and indigenous soil N, and a ‘full-N’ treatment, which provided an ample fertilizer N supply during the entire crop cycle based on novel protocol developed also in this study. Seed yield and protein concentration in full N were 11% and 3% higher than zero-N, respectively. The magnitude of the difference depended upon the yield level of the production environment, ranging from 0 kg ha-1 at 2.5 Mg ha-1 up to 900 kg ha-1 at 6 Mg ha-1. Seed yield responses were directly related with increases in accumulated N in aboveground biomass (70 kg N ha-1), without changes in nitrogen use efficiency. The N limitation was mitigated in environments with large contribution of indigenous soil N supply. The maximum rates of N limitation occurred before the seed filling and the plant mechanisms and processes underlying seed yield and protein concentrations were leaf area index, absorbed solar radiation, and N remobilization. Finally, there was a trade-off between biological N2 fixation and indigenous soil N supply with fixation reduced less than proportional per unit increase in indigenous N sources. There was a temporal asynchrony between biological N2 fixation and N demand, that is, biological N2 fixation was not sufficient to meet plant N demand as the latter increased and the contribution of indigenous soil N supply decreased. The peak of indigenous soil N supply was the most important factor explaining variation in the N limitation across environments. Findings from this study will help to narrow soybean yield gap to meet future food demand. Advisor: Patricio Grassin

Understanding Nitrogen Limitation in Soybean

Meeting soybean demand on existing cropland area for a global population of 9.7 billion people by the year 2050 requires narrowing the existing gap between average producer yield and yield potential. Soybean relies on two sources on nitrogen (N): biological N2 fixation and indigenous soil N supply. As soybean yield continues to increase, it seems critical to know if there is a yield level at which potential contribution of indigenous nitrogen sources and fixation becomes insufficient to meet crop N requirements for high yields, while still maintaining or increasing protein and oil concentration. This study evaluated N limitation across 29 high-yield soybean environments in Argentina and Nebraska from 2015 to 2017. Each environment included a ‘zero-N’ treatment, which forced the crop to rely on biological N2 fixation and indigenous soil N, and a ‘full-N’ treatment, which provided an ample fertilizer N supply during the entire crop cycle based on novel protocol developed also in this study. Seed yield and protein concentration in full N were 11% and 3% higher than zero-N, respectively. The magnitude of the difference depended upon the yield level of the production environment, ranging from 0 kg ha-1 at 2.5 Mg ha-1 up to 900 kg ha-1 at 6 Mg ha-1. Seed yield responses were directly related with increases in accumulated N in aboveground biomass (70 kg N ha-1), without changes in nitrogen use efficiency. The N limitation was mitigated in environments with large contribution of indigenous soil N supply. The maximum rates of N limitation occurred before the seed filling and the plant mechanisms and processes underlying seed yield and protein concentrations were leaf area index, absorbed solar radiation, and N remobilization. Finally, there was a trade-off between biological N2 fixation and indigenous soil N supply with fixation reduced less than proportional per unit increase in indigenous N sources. There was a temporal asynchrony between biological N2 fixation and N demand, that is, biological N2 fixation was not sufficient to meet plant N demand as the latter increased and the contribution of indigenous soil N supply decreased. The peak of indigenous soil N supply was the most important factor explaining variation in the N limitation across environments. Findings from this study will help to narrow soybean yield gap to meet future food demand

Macro and Micro-Nutrient Accumulation and Partitioning in Soybean Affected by Water and Nitrogen Supply

This study aimed to investigate the influence of water availability and nitrogen fertilization on plant growth, nutrient dynamics, and variables related to soybean crop yield. Trials were performed in Teresina, Piauí, Brazil, using randomized blocks in a split-split plot arrangement. The plots corresponded to water regimes (full and deficient), the split plots to N fertilization (0 and 1000 kg ha−1 N-urea), and the split-split plots to harvest times of soybean plants (16, 23, 30, 37, 44, 58, 65, 79 and 86 days after emergence), with three replicates. In general, the accumulation and partitioning of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulphur (S), copper (Cu), iron (Fe), manganese (Mn), zinc (Zn) and boron (B) were decreased in plants subjected to water deficit and without N fertilization. Although nitrogen fertilization promoted elevated N accumulation in tissues, it did not result in any significant yield gain, and the highest seed yields were found in plants under full irrigation, regardless of N supplementation. However, deficient irrigation decreased the seed oil content of N-fertilized plants. In conclusion, N fertilization is critical for nutrient homeostasis, and water availability impairs biomass and nutrient accumulation, thereby limiting soybean yield performance