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.

The objective of this work was to evaluate water storage in a Plinthaqualf under different straw levels during the fourth ratoon season of a sugarcane (Saccharum officinarum) crop. The study was conducted in the 2013/2014 crop season, with the cultivar SP-813250, at two soil depths (0.0-0.3 and 0.3-0.6 m), in a randomized complete block design, with five straw levels (0.0, 4.2, 9.5, 13.0, and 18.4 Mg ha^-1) and four replicates. Soil moisture content was monitored with a time-domain reflectometer. The straw provided gains of up to 20 Mg ha^-1 stems and kept increased water storage in the soil, in comparison with the soil without straw, in all evaluated periods. Maintenance of up to 50% (9.5 Mg ha^-1) of sugarcane straw on soil surface promotes better water retention in the soil per Mg of straw added and delays the reach of critical water storage in the soil by up to 11 days, when compared with soil without straw cover.

Recent researches have shown promising results for the use of orbital data using the Normalized Difference Vegetation Index (NDVI) to monitor and predict soybean grain yield. The objective of this work was to evaluate propositions of multiple linear regression models to predict soybean grain yield using NDVI. The research was carried out at the Celeiro Farm, in Monte Alegre do Piauí, PI, Brazil, in an area of 200 ha. Five images were collected during the soybean crop cycle: one from the Landsat 8 and four from the Sentinel 2. Regression analyses were carried out between grain yield data (predicted variable) extracted from harvest maps and spectral data (predictor variables) from NDVI of soybean crops at different developmental stages. The promising models were selected by the Akaike Information Criterion (AIC). The models were validated using Root Mean Square Error (RMSE) and Normalized Root Mean Square Error (nRMSE), considering the mean of soybean yield of the plot. The linear regression models developed with NDVI for the V5-V6 and R2 developmental stages showed promising results for the prediction of soybean grain yield, with mean error of predictions of 153.9 kg ha-1, representing 4.2% when compared to the data from field measures.

In intercropping systems, a high plant density can delay the biomass accumulation and affect the water availability to plants. This study aimed to evaluate the soil water dynamics and the crop yield performance in maize and Brachiaria ruziziensis intercropping under different sowing densities of the forage grass. The experiment was conducted in a randomized block design, with treatments associated to the sowing densities (2 kg ha^-1, 4 kg ha^-1, 6 kg ha^-1 and 8 kg ha^-1) and the single cropping for both species as controls. The maize plants were evaluated for grain yield and B. ruziziensis for number of plants per hectare and shoot fresh and dry matter. The intercropping performance was evaluated using the land-use efficiency index. The soil water dynamics was monitored in two soil depths (0-0.3 m and 0.3-0.6 m) by using the time domain reflectometry method. The evaluation of soil water storage was carried out from plots with four of the crop systems (single maize or B. ruziziensis, and intercropping with the extreme sowing densities), at four different times. The increase in the sowing density of B. ruziziensis decreased the grain yield of the intercropped maize by 30.8 %. The intercropping system using 2 kg ha^-1 of the grass seeds resulted in the best land-use efficiency (23 %). In addition, the intercropping treatments promoted a higher extraction of water from the soil, mainly at the maize growth stages with higher hydric demand (e.g., flowering and grain filling). These systems stimulate the extraction of water from deeper soil layers, when compared to maize in single cropping.