No abstract

Precision agriculture techniques were employed to study the impact of the spatiotemporal variations of soil compaction on the performance of potato crop during its various growth stages. The study has been conducted on a 30 ha centre pivot irrigated potato field, located in Wadi Al‐Dawasir area in Saudi Arabia. In situ soil compaction measurements were collected, in conjunction with Sentinel‐2A satellite data, and correlated spatiotemporally against potato crop growth and yield parameters. The univariate and bivariate Moran's function (Moran's I), the linear regression and the analysis of variance (ANOVA) techniques were used to analyse the data and examine the interrelationships. The spatial correlations between the measured variables revealed high clustering, producing Moran's I of 0.87, 0.79 and 0.57 for soil compaction, yield and normalized difference vegetation index (NDVI), respectively. Compaction‐yield relationship revealed a relatively high significant negative spatial correlation (Moran's I = 0.68). While, the spatial correlation between the average values of compaction and NDVI has negatively produced a Moran's I value of 0.45 (at 0.001 significance level), when 999 permutations were tested for all relationships. A significant positive correlation was observed between high compaction and high proportion of small size tubers, with R2 and P > F values of 0.65 and .0001, respectively. In contrast, a significant negative correlation has been obtained between high compaction and high proportion of large size tubers, with R2 and P > F values of 0.57 and .0001, respectively. Understanding the causes of disparity in the productivity of agricultural fields will help decision‐makers and farmers to take proactive actions towards better agricultural practices.

The soil organic carbon (SOC) plays a vital role in plant growth and development, and therefore is considered as one of the most important indicators of soil quality. This study was carried out in the central region of Saudi Arabia to explore the potential of spectroscopy in determining the SOC concentration in low-fertility soils. Spectral reflectance data were collected, under the controlled laboratory conditions on 39 air-dried 2.0 mm sieved soil samples, using a handheld spectroradiometer of a wavelength range between 350 nm and 2500 nm in the direct contact probe mode. The concentration of the SOC was determined using the Walkley and Black (W&B) and the UV-VIS spectrophotometric methods. The increase in the concentration of SOC was associated with a decrease in the corresponding spectral reflectance. Regression analysis showed linear relationships with high significant correlation between the spectral reflectance and the SOC measured by both the UV-VIS (Model-1: R 2 =0.46, p=0.00015 and RMSE=6.6 g/kg) and the W&B (Model-2: R 2 =0.48, p=8.92E-05 and RMSE= 2.8 g/kg) methods. For these models, two wavebands with wavelengths of 2167 nm (Model-1) and 1359 nm (Model-2) were identified as the most sensitive bands to the SOC concentration. The cross-validation confirmed the validity of Model-1 with R 2 , p and RMSE values of 0.50, 0.0099 and 6.6 g/kg, respectively. The validation results of the Model-2 showed values of R 2 , p and RMSE of 0.72, 0.00023 and 4.0 g/kg, respectively. Results of this study revealed the possibility and the potential of using the spectral reflectance technique in predicting the concentration of SOC.

A study on a 30 hm 2 field was conducted to assess the variability in soil compaction and to investigate its effect on the engineering properties of potato tubers in terms of tuber shape and key dimensions (length, width and thickness) and resistance to penetration, rupture and shear forces. Three soil compaction levels were spatially correlated with the engineering properties of potato tubers through linear regression and ANOVA test. The three compaction levels included a low level (C1) ranging between 1.2-1.9 MPa, a medium level (C2) with compaction levels between 2.0-2.3 MPa and a high level (C3) ranging between 2.4-2.9 MPa. Results revealed that there were no significant changes in the key tuber dimensions corresponding to the variability in soil compaction. However, inverse linear relationships were observed between soil compaction and the key tuber dimensions with R 2 values of 77%, 97% and 96% for length, width and thickness, respectively. Similarly, the soil compaction was shown to have no effect on the tuber resistance to compression and shear force. In contrast, the tuber resistance to penetration was significantly affected by soil compaction (p>F = 0.0012).

Maintaining the homogeneity of soil nitrogen (N) and plant vigor across agricultural fields is a major concern for farmers and agricultural scheme planners, particularly fields that are irrigated through pressurized systems, such as center pivots. Therefore, this study was carried out on a 30 hm 2 potato field located 650 km south of Riyadh, the capital city of the Kingdom of Saudi Arabia, to investigate the impacts of the center pivot irrigation distribution uniformity on the crop development and the spatial distribution of residual soil N. Irrigation performance test was designed to investigate water application rate and distribution uniformities. The overall water application uniformity coefficients (Cu), determined through Christiansen (Cud) and Heerman (CuH) methods, were determined at 81.29% and 80.64%, respectively. However, the overall water distribution uniformity (Du) was determined at 70%. A considerable variability in the distribution uniformity of irrigation water was observed across the experimental field (a Du value of 67% over the medium spans compared to a Du value of 88% over the inner spans). Results of this study showed a linear correlation between the irrigation water distribution uniformity and the soil N (R 2 = 0 .88). On the other hand, the vegetation cover distribution, indicated by the Cumulative Normalized Difference Vegetation Index (CNDVI), was not found to be much responsive to the irrigation distribution uniformity (R 2 = 0 .11). A time series of successive NDVI maps extracted throughout the potato crop growth stages showed a consistent trend in the distribution of NDVI across the field, with R 2 values that ranged between 0.25-0.73.