Seed Nutritional Quality of Chickpea (Cicer arietinum L.) as Influenced by Rice Husk Form and Humic Acid Rate under Rainfed Conditions in Northern Iraq

Chickpea (Cicer arietinum L.) cultivation in the Kurdistan Region of Iraq faces severe constraints due to low-organic-matter calcareous soils and highly erratic rainfall. This study offers novel empirical insights by directly comparing the joint impacts of raw versus carbonized rice husk and humic acid under rainfed calcareous soil conditions. To address these limitations, a field experiment was conducted during the 2022–2023 rainfed season in Ranya, Sulaymaniyah, evaluating the effects of rice husk treatments and humic acid application on the growth, yield, and nutritional profile of chickpea (cv. Piramerd). The study followed a 3x5 factorial arrangement in a randomized complete block design (RCBD) with three replications, testing three rice husk forms-none (B0), carbonized (B1), and raw (B2), each at 6.67 t ha^-1 -across five humic acid doses (0, 10, 20, 30, and 40 kg ha^-1). Analysis of variance showed that neither the individual factors nor their interaction significantly altered vegetative growth parameters (plant height, branch and nodule counts, leaf area) or overall seed and straw yields. The only yield component sensitive to the treatments was the seed index (p=0.022), which responded solely to the humic acid main effect; the highest 100-seed weight was recorded in the control group (43.43 g), whereas the 20 kg ha^-1 dose yielded the lowest (37.69 g). Conversely, the nutritional profile of the harvest was highly responsive to the treatments, with all six proximate composition parameters (moisture, ash, crude fiber, crude protein, total carbohydrates, and crude oil) exhibiting significant interaction effects (p≤0.007). Notably, the combination of raw rice husk and the highest humic acid rate (B2H4) optimized both crude protein (23.25%) and total carbohydrates (61.14%), compared to the 19.85% protein and 55.86% carbohydrate baselines observed in the control (B0H0). Principal component analysis (PCA) captured 57.9% of the total variance across two main axes, separating a yield–biomass dimension (PC1, 38.8%) from a moisture–growth axis (PC2, 19.1%). Ultimately, these results demonstrate that while soil amendment with rice husk and humic acid does not drive biomass accumulation under rainfed stress, it plays a critical role in modulating the metabolic and nutritional quality of chickpea seeds-a nuance that offers valuable insights for quality-focused breeding and fertility management in semi-arid pulse production.